Re: [RFC PATCH v1 11/50] Treewide: Extirpate "prandom_u32() % range"

[Jan Kara <jack@xxxxxxx>]

On Mon 18-03-19 01:46:20, George Spelvin wrote:
> % is fast to type but slow to compute.  Even if the range is
> a compile-time constant, the code is two multiplications (one by a
> reciprocal approximation, then a second to compute the modulus).
> 
> prandom_u32_max() is one multiply, so always smaller and faster.
> 
> This patch is all the simple cases; ones requiring a bit of thought
> are separated out.
> 
> If the range is a power of 2, both variants optimize to one cheap
> instruction, so conversion is optional.  In general, I've converted
> when the range is a #define which is not immediately obvious is a
> power of 2 (e.g. ROLLOVER_HLEN in net/packet/af_packet.c), but not
> when it's a manifest constant (e.g. crypto/testmgr.c).
> 
> The one time the caller needs to optimize specially
> is if range is a variable power of 2.

Honestly, I think that a microoptimization like this will bring any benefit
only in the fast paths and e.g. most of the filesystem places aren't like
that as far as I've checked. OTOH it doesn't hurt readability so I'm not
opposed either. So feel free to add:

Acked-by: Jan Kara <jack@xxxxxxx>

for ext2 and ext4 bits.

								Honza

> 
> Signed-off-by: George Spelvin <lkml@xxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> (maintainer:X86 MM)
> Cc: Andy Lutomirski <luto@xxxxxxxxxx> (maintainer:X86 MM)
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> (maintainer:X86 MM)
> Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> (maintainer:CRYPTO API)
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx> (maintainer:CRYPTO API)
> Cc: Atul Gupta <atul.gupta@xxxxxxxxxxx> (supporter:CXGB4 CRYPTO DRIVER (chcr))
> Cc: linux-crypto@xxxxxxxxxxxxxxx (open list:CRYPTO API)
> Cc: Doug Ledford <dledford@xxxxxxxxxx> (supporter:INFINIBAND SUBSYSTEM)
> Cc: Jason Gunthorpe <jgg@xxxxxxxx> (supporter:INFINIBAND SUBSYSTEM)
> Cc: Potnuri Bharat Teja <bharat@xxxxxxxxxxx> (supporter:CXGB4 IWARP RNIC DRIVER (IW_CXGB4))
> Cc: linux-rdma@xxxxxxxxxxxxxxx (open list:INFINIBAND SUBSYSTEM)
> Cc: Ulf Hansson <ulf.hansson@xxxxxxxxxx> (maintainer:MULTIMEDIA CARD (MMC), SECURE DIGITAL (SD) AND...)
> Cc: linux-mmc@xxxxxxxxxxxxxxx (open list:MULTIMEDIA CARD (MMC), SECURE DIGITAL (SD) AND...)
> Cc: Miquel Raynal <miquel.raynal@xxxxxxxxxxx> (maintainer:NAND FLASH SUBSYSTEM)
> Cc: Richard Weinberger <richard@xxxxxx> (reviewer:NAND FLASH SUBSYSTEM)
> Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx> (maintainer:MEMORY TECHNOLOGY DEVICES (MTD))
> Cc: Brian Norris <computersforpeace@xxxxxxxxx> (maintainer:MEMORY TECHNOLOGY DEVICES (MTD))
> Cc: Marek Vasut <marek.vasut@xxxxxxxxx> (maintainer:MEMORY TECHNOLOGY DEVICES (MTD))
> Cc: Vignesh Raghavendra <vigneshr@xxxxxx> (maintainer:MEMORY TECHNOLOGY DEVICES (MTD))
> Cc: Artem Bityutskiy <dedekind1@xxxxxxxxx> (supporter:UNSORTED BLOCK IMAGES (UBI))
> Cc: linux-mtd@xxxxxxxxxxxxxxxxxxx (open list:NAND FLASH SUBSYSTEM)
> Cc: netdev@xxxxxxxxxxxxxxx (open list:NETWORKING DRIVERS)
> Cc: Arend van Spriel <arend.vanspriel@xxxxxxxxxxxx> (supporter:BROADCOM BRCM80211 IEEE802.11n WIRELESS DRIVER)
> Cc: Franky Lin <franky.lin@xxxxxxxxxxxx> (supporter:BROADCOM BRCM80211 IEEE802.11n WIRELESS DRIVER)
> Cc: Hante Meuleman <hante.meuleman@xxxxxxxxxxxx> (supporter:BROADCOM BRCM80211 IEEE802.11n WIRELESS DRIVER)
> Cc: Chi-Hsien Lin <chi-hsien.lin@xxxxxxxxxxx> (supporter:BROADCOM BRCM80211 IEEE802.11n WIRELESS DRIVER)
> Cc: Wright Feng <wright.feng@xxxxxxxxxxx> (supporter:BROADCOM BRCM80211 IEEE802.11n WIRELESS DRIVER)
> Cc: brcm80211-dev-list.pdl@xxxxxxxxxxxx (open list:BROADCOM BRCM80211 IEEE802.11n WIRELESS DRIVER)
> Cc: brcm80211-dev-list@xxxxxxxxxxx (open list:BROADCOM BRCM80211 IEEE802.11n WIRELESS DRIVER)
> Cc: Kalle Valo <kvalo@xxxxxxxxxxxxxx> (maintainer:NETWORKING DRIVERS (WIRELESS))
> Cc: Johannes Berg <johannes.berg@xxxxxxxxx> (supporter:INTEL WIRELESS WIFI LINK (iwlwifi))
> Cc: Emmanuel Grumbach <emmanuel.grumbach@xxxxxxxxx> (supporter:INTEL WIRELESS WIFI LINK (iwlwifi))
> Cc: Luca Coelho <luciano.coelho@xxxxxxxxx> (supporter:INTEL WIRELESS WIFI LINK (iwlwifi))
> Cc: Intel Linux Wireless <linuxwifi@xxxxxxxxx> (supporter:INTEL WIRELESS WIFI LINK (iwlwifi))
> Cc: linux-wireless@xxxxxxxxxxxxxxx (open list:BROADCOM BRCM80211 IEEE802.11n WIRELESS DRIVER)
> Cc: Hannes Reinecke <hare@xxxxxxx> (supporter:FCOE SUBSYSTEM (libfc, libfcoe, fcoe))
> Cc: QLogic-Storage-Upstream@xxxxxxxxxx (supporter:QLOGIC QL41xxx ISCSI DRIVER)
> Cc: linux-scsi@xxxxxxxxxxxxxxx (open list:FCOE SUBSYSTEM (libfc, libfcoe, fcoe))
> Cc: Jeff Layton <jlayton@xxxxxxxxxx> (supporter:CEPH DISTRIBUTED FILE SYSTEM CLIENT (CEPH))
> Cc: Sage Weil <sage@xxxxxxxxxx> (supporter:CEPH DISTRIBUTED FILE SYSTEM CLIENT (CEPH))
> Cc: Ilya Dryomov <idryomov@xxxxxxxxx> (supporter:CEPH DISTRIBUTED FILE SYSTEM CLIENT (CEPH))
> Cc: ceph-devel@xxxxxxxxxxxxxxx (open list:CEPH DISTRIBUTED FILE SYSTEM CLIENT (CEPH))
> Cc: Jan Kara <jack@xxxxxxxx> (maintainer:EXT2 FILE SYSTEM)
> Cc: "Theodore Ts'o" <tytso@xxxxxxx> (maintainer:EXT4 FILE SYSTEM)
> Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx> (maintainer:EXT4 FILE SYSTEM)
> Cc: linux-ext4@xxxxxxxxxxxxxxx (open list:EXT2 FILE SYSTEM)
> Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx> (supporter:UBI FILE SYSTEM (UBIFS))
> Cc: "Darrick J. Wong" <darrick.wong@xxxxxxxxxx> (supporter:XFS FILESYSTEM)
> Cc: linux-xfs@xxxxxxxxxxxxxxx (supporter:XFS FILESYSTEM)
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> (maintainer:MEMORY MANAGEMENT)
> Cc: linux-mm@xxxxxxxxx (open list:MEMORY MANAGEMENT)
> Cc: Marek Lindner <mareklindner@xxxxxxxxxxxxx> (maintainer:BATMAN ADVANCED)
> Cc: Simon Wunderlich <sw@xxxxxxxxxxxxxxxxxx> (maintainer:BATMAN ADVANCED)
> Cc: Antonio Quartulli <a@xxxxxxxxxxx> (maintainer:BATMAN ADVANCED)
> Cc: Sven Eckelmann <sven@xxxxxxxxxxxxx> (maintainer:BATMAN ADVANCED)
> Cc: b.a.t.m.a.n@xxxxxxxxxxxxxxxxxxx (moderated list:BATMAN ADVANCED)
> Cc: Alexey Kuznetsov <kuznet@xxxxxxxxxxxxx> (maintainer:NETWORKING [IPv4/IPv6])
> Cc: Hideaki YOSHIFUJI <yoshfuji@xxxxxxxxxxxxxx> (maintainer:NETWORKING [IPv4/IPv6])
> Cc: Jamal Hadi Salim <jhs@xxxxxxxxxxxx> (maintainer:TC subsystem)
> Cc: Cong Wang <xiyou.wangcong@xxxxxxxxx> (maintainer:TC subsystem)
> Cc: Jiri Pirko <jiri@xxxxxxxxxxx> (maintainer:TC subsystem)
> Cc: Stephen Hemminger <stephen@xxxxxxxxxxxxxxxxxx> (maintainer:NETEM NETWORK EMULATOR)
> Cc: netem@xxxxxxxxxxxxxxxxxxxxxxxxxx (moderated list:NETEM NETWORK EMULATOR)
> Cc: Vlad Yasevich <vyasevich@xxxxxxxxx> (maintainer:SCTP PROTOCOL)
> Cc: Neil Horman <nhorman@xxxxxxxxxxxxx> (maintainer:SCTP PROTOCOL,added_lines:17/168=10%)
> Cc: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx> (maintainer:SCTP PROTOCOL)
> Cc: linux-sctp@xxxxxxxxxxxxxxx (open list:SCTP PROTOCOL)
> Cc: "J. Bruce Fields" <bfields@xxxxxxxxxxxx> (supporter:KERNEL NFSD, SUNRPC, AND LOCKD SERVERS)
> Cc: Chuck Lever <chuck.lever@xxxxxxxxxx> (supporter:KERNEL NFSD, SUNRPC, AND LOCKD SERVERS)
> Cc: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> (maintainer:NFS, SUNRPC, AND LOCKD CLIENTS)
> Cc: Anna Schumaker <anna.schumaker@xxxxxxxxxx> (maintainer:NFS, SUNRPC, AND LOCKD CLIENTS)
> Cc: linux-nfs@xxxxxxxxxxxxxxx (open list:KERNEL NFSD, SUNRPC, AND LOCKD SERVERS)
> Cc: Jon Maloy <jon.maloy@xxxxxxxxxxxx> (maintainer:TIPC NETWORK LAYER)
> Cc: Ying Xue <ying.xue@xxxxxxxxxxxxx> (maintainer:TIPC NETWORK LAYER)
> Cc: tipc-discussion@xxxxxxxxxxxxxxxxxxxxx (open list:TIPC NETWORK LAYER)
> Cc: Steffen Klassert <steffen.klassert@xxxxxxxxxxx> (maintainer:NETWORKING [IPSEC])
> ---
>  arch/x86/mm/pageattr-test.c                   |  4 ++--
>  crypto/testmgr.c                              | 16 +++++++--------
>  drivers/crypto/chelsio/chtls/chtls_io.c       |  4 ++--
>  drivers/infiniband/core/cma.c                 |  2 +-
>  drivers/infiniband/hw/cxgb4/id_table.c        |  4 ++--
>  drivers/mmc/core/core.c                       |  4 ++--
>  drivers/mtd/nand/raw/nandsim.c                |  4 ++--
>  drivers/mtd/tests/mtd_nandecctest.c           | 10 +++++-----
>  drivers/mtd/tests/stresstest.c                | 15 +++-----------
>  drivers/mtd/ubi/debug.c                       |  2 +-
>  drivers/net/ethernet/broadcom/cnic.c          |  3 +--
>  .../broadcom/brcm80211/brcmfmac/p2p.c         |  2 +-
>  .../net/wireless/intel/iwlwifi/mvm/mac-ctxt.c |  2 +-
>  drivers/scsi/qedi/qedi_main.c                 |  2 +-
>  fs/ceph/inode.c                               |  2 +-
>  fs/ceph/mdsmap.c                              |  2 +-
>  fs/ext2/ialloc.c                              |  3 +--
>  fs/ext4/super.c                               |  8 ++++----
>  fs/ubifs/debug.c                              |  6 +++---
>  fs/ubifs/lpt_commit.c                         | 12 +++++------
>  fs/xfs/xfs_error.c                            |  2 +-
>  lib/find_bit_benchmark.c                      |  4 ++--
>  lib/sbitmap.c                                 |  7 ++++---
>  lib/test_list_sort.c                          |  2 +-
>  mm/swapfile.c                                 |  2 +-
>  net/batman-adv/bat_iv_ogm.c                   |  2 +-
>  net/batman-adv/bat_v_elp.c                    |  2 +-
>  net/batman-adv/bat_v_ogm.c                    |  2 +-
>  net/ceph/mon_client.c                         |  2 +-
>  net/core/neighbour.c                          |  6 +++---
>  net/core/pktgen.c                             | 20 +++++++++----------
>  net/core/stream.c                             |  2 +-
>  net/ipv4/igmp.c                               |  6 +++---
>  net/ipv4/inet_connection_sock.c               |  2 +-
>  net/ipv6/addrconf.c                           |  2 +-
>  net/ipv6/mcast.c                              | 10 +++++-----
>  net/packet/af_packet.c                        |  2 +-
>  net/sched/act_gact.c                          |  2 +-
>  net/sched/act_sample.c                        |  2 +-
>  net/sched/sch_netem.c                         |  7 +++----
>  net/sctp/socket.c                             |  2 +-
>  net/sunrpc/xprtsock.c                         |  2 +-
>  net/tipc/socket.c                             |  5 ++---
>  net/xfrm/xfrm_state.c                         |  2 +-
>  44 files changed, 96 insertions(+), 108 deletions(-)
> 
> diff --git a/arch/x86/mm/pageattr-test.c b/arch/x86/mm/pageattr-test.c
> index facce271e8b93..d184def2c3d49 100644
> --- a/arch/x86/mm/pageattr-test.c
> +++ b/arch/x86/mm/pageattr-test.c
> @@ -137,10 +137,10 @@ static int pageattr_test(void)
>  	failed += print_split(&sa);
>  
>  	for (i = 0; i < NTEST; i++) {
> -		unsigned long pfn = prandom_u32() % max_pfn_mapped;
> +		unsigned long pfn = prandom_u32_max(max_pfn_mapped);
>  
>  		addr[i] = (unsigned long)__va(pfn << PAGE_SHIFT);
> -		len[i] = prandom_u32() % NPAGES;
> +		len[i] = prandom_u32_max(NPAGES);
>  		len[i] = min_t(unsigned long, len[i], max_pfn_mapped - pfn - 1);
>  
>  		if (len[i] == 0)
> diff --git a/crypto/testmgr.c b/crypto/testmgr.c
> index 2c96963b2e51e..e8f21f7348a48 100644
> --- a/crypto/testmgr.c
> +++ b/crypto/testmgr.c
> @@ -745,7 +745,7 @@ static int build_cipher_test_sglists(struct cipher_test_sglists *tsgls,
>  /* Generate a random length in range [0, max_len], but prefer smaller values */
>  static unsigned int generate_random_length(unsigned int max_len)
>  {
> -	unsigned int len = prandom_u32() % (max_len + 1);
> +	unsigned int len = prandom_u32_max(max_len + 1);
>  
>  	switch (prandom_u32() % 4) {
>  	case 0:
> @@ -779,7 +779,7 @@ static void mutate_buffer(u8 *buf, size_t count)
>  	if (prandom_u32() % 4 == 0) {
>  		num_flips = min_t(size_t, 1 << (prandom_u32() % 8), count);
>  		for (i = 0; i < num_flips; i++)
> -			buf[prandom_u32() % count] ^= 0xff;
> +			buf[prandom_u32_max(count)] ^= 0xff;
>  	}
>  }
>  
> @@ -840,7 +840,7 @@ static char *generate_random_sgl_divisions(struct test_sg_division *divs,
>  		if (div == &divs[max_divs - 1] || prandom_u32() % 2 == 0)
>  			this_len = remaining;
>  		else
> -			this_len = 1 + (prandom_u32() % remaining);
> +			this_len = 1 + prandom_u32_max(remaining);
>  		div->proportion_of_total = this_len;
>  
>  		if (prandom_u32() % 4 == 0)
> @@ -962,7 +962,7 @@ static void generate_random_testvec_config(struct testvec_config *cfg,
>  	}
>  
>  	if (prandom_u32() % 2 == 0) {
> -		cfg->iv_offset = 1 + (prandom_u32() % MAX_ALGAPI_ALIGNMASK);
> +		cfg->iv_offset = 1 + prandom_u32_max(MAX_ALGAPI_ALIGNMASK);
>  		p += scnprintf(p, end - p, " iv_offset=%u", cfg->iv_offset);
>  	}
>  
> @@ -1522,7 +1522,7 @@ static void generate_random_hash_testvec(struct shash_desc *desc,
>  	if (maxkeysize) {
>  		vec->ksize = maxkeysize;
>  		if (prandom_u32() % 4 == 0)
> -			vec->ksize = 1 + (prandom_u32() % maxkeysize);
> +			vec->ksize = 1 + prandom_u32_max(maxkeysize);
>  		generate_random_bytes((u8 *)vec->key, vec->ksize);
>  
>  		vec->setkey_error = crypto_shash_setkey(desc->tfm, vec->key,
> @@ -2070,7 +2070,7 @@ static void generate_random_aead_testvec(struct aead_request *req,
>  	/* Key: length in [0, maxkeysize], but usually choose maxkeysize */
>  	vec->klen = maxkeysize;
>  	if (prandom_u32() % 4 == 0)
> -		vec->klen = prandom_u32() % (maxkeysize + 1);
> +		vec->klen = prandom_u32_max(maxkeysize + 1);
>  	generate_random_bytes((u8 *)vec->key, vec->klen);
>  	vec->setkey_error = crypto_aead_setkey(tfm, vec->key, vec->klen);
>  
> @@ -2080,7 +2080,7 @@ static void generate_random_aead_testvec(struct aead_request *req,
>  	/* Tag length: in [0, maxauthsize], but usually choose maxauthsize */
>  	authsize = maxauthsize;
>  	if (prandom_u32() % 4 == 0)
> -		authsize = prandom_u32() % (maxauthsize + 1);
> +		authsize = prandom_u32_max(maxauthsize + 1);
>  	if (WARN_ON(authsize > maxdatasize))
>  		authsize = maxdatasize;
>  	maxdatasize -= authsize;
> @@ -2659,7 +2659,7 @@ static void generate_random_cipher_testvec(struct skcipher_request *req,
>  	/* Key: length in [0, maxkeysize], but usually choose maxkeysize */
>  	vec->klen = maxkeysize;
>  	if (prandom_u32() % 4 == 0)
> -		vec->klen = prandom_u32() % (maxkeysize + 1);
> +		vec->klen = prandom_u32_max(maxkeysize + 1);
>  	generate_random_bytes((u8 *)vec->key, vec->klen);
>  	vec->setkey_error = crypto_skcipher_setkey(tfm, vec->key, vec->klen);
>  
> diff --git a/drivers/crypto/chelsio/chtls/chtls_io.c b/drivers/crypto/chelsio/chtls/chtls_io.c
> index 5cf9b021220b8..5427b61926bba 100644
> --- a/drivers/crypto/chelsio/chtls/chtls_io.c
> +++ b/drivers/crypto/chelsio/chtls/chtls_io.c
> @@ -927,8 +927,8 @@ static int csk_wait_memory(struct chtls_dev *cdev,
>  	current_timeo = *timeo_p;
>  	noblock = (*timeo_p ? false : true);
>  	if (csk_mem_free(cdev, sk)) {
> -		current_timeo = (prandom_u32() % (HZ / 5)) + 2;
> -		vm_wait = (prandom_u32() % (HZ / 5)) + 2;
> +		current_timeo = prandom_u32_max(HZ / 5) + 2;
> +		vm_wait = prandom_u32_max(HZ / 5) + 2;
>  	}
>  
>  	add_wait_queue(sk_sleep(sk), &wait);
> diff --git a/drivers/infiniband/core/cma.c b/drivers/infiniband/core/cma.c
> index 0b530646f1e51..a5874d2fac54e 100644
> --- a/drivers/infiniband/core/cma.c
> +++ b/drivers/infiniband/core/cma.c
> @@ -3366,7 +3366,7 @@ static int cma_alloc_any_port(enum rdma_ucm_port_space ps,
>  
>  	inet_get_local_port_range(net, &low, &high);
>  	remaining = (high - low) + 1;
> -	rover = prandom_u32() % remaining + low;
> +	rover = prandom_u32_max(remaining) + low;
>  retry:
>  	if (last_used_port != rover) {
>  		struct rdma_bind_list *bind_list;
> diff --git a/drivers/infiniband/hw/cxgb4/id_table.c b/drivers/infiniband/hw/cxgb4/id_table.c
> index 724d23297b355..edcae6af65d6c 100644
> --- a/drivers/infiniband/hw/cxgb4/id_table.c
> +++ b/drivers/infiniband/hw/cxgb4/id_table.c
> @@ -54,7 +54,7 @@ u32 c4iw_id_alloc(struct c4iw_id_table *alloc)
>  
>  	if (obj < alloc->max) {
>  		if (alloc->flags & C4IW_ID_TABLE_F_RANDOM)
> -			alloc->last += prandom_u32() % RANDOM_SKIP;
> +			alloc->last += prandom_u32_max(RANDOM_SKIP);
>  		else
>  			alloc->last = obj + 1;
>  		if (alloc->last >= alloc->max)
> @@ -87,7 +87,7 @@ int c4iw_id_table_alloc(struct c4iw_id_table *alloc, u32 start, u32 num,
>  	alloc->start = start;
>  	alloc->flags = flags;
>  	if (flags & C4IW_ID_TABLE_F_RANDOM)
> -		alloc->last = prandom_u32() % RANDOM_SKIP;
> +		alloc->last = prandom_u32_max(RANDOM_SKIP);
>  	else
>  		alloc->last = 0;
>  	alloc->max  = num;
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index abf8f5eb0a1c8..77ecf5fa6c1b4 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -96,8 +96,8 @@ static void mmc_should_fail_request(struct mmc_host *host,
>  	    !should_fail(&host->fail_mmc_request, data->blksz * data->blocks))
>  		return;
>  
> -	data->error = data_errors[prandom_u32() % ARRAY_SIZE(data_errors)];
> -	data->bytes_xfered = (prandom_u32() % (data->bytes_xfered >> 9)) << 9;
> +	data->error = data_errors[prandom_u32_max(ARRAY_SIZE(data_errors))];
> +	data->bytes_xfered = prandom_u32_max(data->bytes_xfered >> 9) << 9;
>  }
>  
>  #else /* CONFIG_FAIL_MMC_REQUEST */
> diff --git a/drivers/mtd/nand/raw/nandsim.c b/drivers/mtd/nand/raw/nandsim.c
> index 9a70754a61efe..3bed07d9feab3 100644
> --- a/drivers/mtd/nand/raw/nandsim.c
> +++ b/drivers/mtd/nand/raw/nandsim.c
> @@ -1391,9 +1391,9 @@ static void do_bit_flips(struct nandsim *ns, int num)
>  	if (bitflips && prandom_u32() < (1 << 22)) {
>  		int flips = 1;
>  		if (bitflips > 1)
> -			flips = (prandom_u32() % (int) bitflips) + 1;
> +			flips = prandom_u32_max(bitflips) + 1;
>  		while (flips--) {
> -			int pos = prandom_u32() % (num * 8);
> +			int pos = prandom_u32_max(num * 8);
>  			ns->buf.byte[pos / 8] ^= (1 << (pos % 8));
>  			NS_WARN("read_page: flipping bit %d in page %d "
>  				"reading from %d ecc: corrected=%u failed=%u\n",
> diff --git a/drivers/mtd/tests/mtd_nandecctest.c b/drivers/mtd/tests/mtd_nandecctest.c
> index 13bca9ea0caef..aac8aa8dac96c 100644
> --- a/drivers/mtd/tests/mtd_nandecctest.c
> +++ b/drivers/mtd/tests/mtd_nandecctest.c
> @@ -47,7 +47,7 @@ struct nand_ecc_test {
>  static void single_bit_error_data(void *error_data, void *correct_data,
>  				size_t size)
>  {
> -	unsigned int offset = prandom_u32() % (size * BITS_PER_BYTE);
> +	unsigned int offset = prandom_u32_max(size * BITS_PER_BYTE);
>  
>  	memcpy(error_data, correct_data, size);
>  	__change_bit_le(offset, error_data);
> @@ -58,9 +58,9 @@ static void double_bit_error_data(void *error_data, void *correct_data,
>  {
>  	unsigned int offset[2];
>  
> -	offset[0] = prandom_u32() % (size * BITS_PER_BYTE);
> +	offset[0] = prandom_u32_max(size * BITS_PER_BYTE);
>  	do {
> -		offset[1] = prandom_u32() % (size * BITS_PER_BYTE);
> +		offset[1] = prandom_u32_max(size * BITS_PER_BYTE);
>  	} while (offset[0] == offset[1]);
>  
>  	memcpy(error_data, correct_data, size);
> @@ -71,7 +71,7 @@ static void double_bit_error_data(void *error_data, void *correct_data,
>  
>  static unsigned int random_ecc_bit(size_t size)
>  {
> -	unsigned int offset = prandom_u32() % (3 * BITS_PER_BYTE);
> +	unsigned int offset = prandom_u32_max(3 * BITS_PER_BYTE);
>  
>  	if (size == 256) {
>  		/*
> @@ -79,7 +79,7 @@ static unsigned int random_ecc_bit(size_t size)
>  		 * and 17th bit) in ECC code for 256 byte data block
>  		 */
>  		while (offset == 16 || offset == 17)
> -			offset = prandom_u32() % (3 * BITS_PER_BYTE);
> +			offset = prandom_u32_max(3 * BITS_PER_BYTE);
>  	}
>  
>  	return offset;
> diff --git a/drivers/mtd/tests/stresstest.c b/drivers/mtd/tests/stresstest.c
> index cb29c8c1b3703..58b307fa85f5d 100644
> --- a/drivers/mtd/tests/stresstest.c
> +++ b/drivers/mtd/tests/stresstest.c
> @@ -45,9 +45,8 @@ static int rand_eb(void)
>  	unsigned int eb;
>  
>  again:
> -	eb = prandom_u32();
>  	/* Read or write up 2 eraseblocks at a time - hence 'ebcnt - 1' */
> -	eb %= (ebcnt - 1);
> +	eb = prandom_u32_max(ebcnt - 1);
>  	if (bbt[eb])
>  		goto again;
>  	return eb;
> @@ -55,20 +54,12 @@ static int rand_eb(void)
>  
>  static int rand_offs(void)
>  {
> -	unsigned int offs;
> -
> -	offs = prandom_u32();
> -	offs %= bufsize;
> -	return offs;
> +	return prandom_u32_max(bufsize);
>  }
>  
>  static int rand_len(int offs)
>  {
> -	unsigned int len;
> -
> -	len = prandom_u32();
> -	len %= (bufsize - offs);
> -	return len;
> +	return prandom_u32_max(bufsize - offs);
>  }
>  
>  static int do_read(void)
> diff --git a/drivers/mtd/ubi/debug.c b/drivers/mtd/ubi/debug.c
> index 54646c2c2744a..9fddb9416cfe9 100644
> --- a/drivers/mtd/ubi/debug.c
> +++ b/drivers/mtd/ubi/debug.c
> @@ -598,7 +598,7 @@ int ubi_dbg_power_cut(struct ubi_device *ubi, int caller)
>  
>  		if (ubi->dbg.power_cut_max > ubi->dbg.power_cut_min) {
>  			range = ubi->dbg.power_cut_max - ubi->dbg.power_cut_min;
> -			ubi->dbg.power_cut_counter += prandom_u32() % range;
> +			ubi->dbg.power_cut_counter += prandom_u32_max(range);
>  		}
>  		return 0;
>  	}
> diff --git a/drivers/net/ethernet/broadcom/cnic.c b/drivers/net/ethernet/broadcom/cnic.c
> index 61ab7d21f6bd6..895f8ef8b50ab 100644
> --- a/drivers/net/ethernet/broadcom/cnic.c
> +++ b/drivers/net/ethernet/broadcom/cnic.c
> @@ -4106,8 +4106,7 @@ static int cnic_cm_alloc_mem(struct cnic_dev *dev)
>  	for (i = 0; i < MAX_CM_SK_TBL_SZ; i++)
>  		atomic_set(&cp->csk_tbl[i].ref_count, 0);
>  
> -	port_id = prandom_u32();
> -	port_id %= CNIC_LOCAL_PORT_RANGE;
> +	port_id = prandom_u32_max(CNIC_LOCAL_PORT_RANGE);
>  	if (cnic_init_id_tbl(&cp->csk_port_tbl, CNIC_LOCAL_PORT_RANGE,
>  			     CNIC_LOCAL_PORT_MIN, port_id)) {
>  		cnic_cm_free_mem(dev);
> diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/p2p.c b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/p2p.c
> index 1f5deea5a288e..84b359ccf669d 100644
> --- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/p2p.c
> +++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/p2p.c
> @@ -1107,7 +1107,7 @@ static void brcmf_p2p_afx_handler(struct work_struct *work)
>  	if (afx_hdl->is_listen && afx_hdl->my_listen_chan)
>  		/* 100ms ~ 300ms */
>  		err = brcmf_p2p_discover_listen(p2p, afx_hdl->my_listen_chan,
> -						100 * (1 + prandom_u32() % 3));
> +						100 * (1 + prandom_u32_max(3)));
>  	else
>  		err = brcmf_p2p_act_frm_search(p2p, afx_hdl->peer_listen_chan);
>  
> diff --git a/drivers/net/wireless/intel/iwlwifi/mvm/mac-ctxt.c b/drivers/net/wireless/intel/iwlwifi/mvm/mac-ctxt.c
> index b78992e341d5e..b740cda037d75 100644
> --- a/drivers/net/wireless/intel/iwlwifi/mvm/mac-ctxt.c
> +++ b/drivers/net/wireless/intel/iwlwifi/mvm/mac-ctxt.c
> @@ -1132,7 +1132,7 @@ static void iwl_mvm_mac_ctxt_cmd_fill_ap(struct iwl_mvm *mvm,
>  			iwl_mvm_mac_ap_iterator, &data);
>  
>  		if (data.beacon_device_ts) {
> -			u32 rand = (prandom_u32() % (64 - 36)) + 36;
> +			u32 rand = prandom_u32_max(64 - 36) + 36;
>  			mvmvif->ap_beacon_time = data.beacon_device_ts +
>  				ieee80211_tu_to_usec(data.beacon_int * rand /
>  						     100);
> diff --git a/drivers/scsi/qedi/qedi_main.c b/drivers/scsi/qedi/qedi_main.c
> index acb930b8c6a64..3f29bbb605e24 100644
> --- a/drivers/scsi/qedi/qedi_main.c
> +++ b/drivers/scsi/qedi/qedi_main.c
> @@ -609,7 +609,7 @@ static int qedi_cm_alloc_mem(struct qedi_ctx *qedi)
>  				sizeof(struct qedi_endpoint *)), GFP_KERNEL);
>  	if (!qedi->ep_tbl)
>  		return -ENOMEM;
> -	port_id = prandom_u32() % QEDI_LOCAL_PORT_RANGE;
> +	port_id = prandom_u32_max(QEDI_LOCAL_PORT_RANGE);
>  	if (qedi_init_id_tbl(&qedi->lcl_port_tbl, QEDI_LOCAL_PORT_RANGE,
>  			     QEDI_LOCAL_PORT_MIN, port_id)) {
>  		qedi_cm_free_mem(qedi);
> diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
> index c07407586ce87..aa658f35ada26 100644
> --- a/fs/ceph/inode.c
> +++ b/fs/ceph/inode.c
> @@ -332,7 +332,7 @@ static int ceph_fill_fragtree(struct inode *inode,
>  	if (nsplits != ci->i_fragtree_nsplits) {
>  		update = true;
>  	} else if (nsplits) {
> -		i = prandom_u32() % nsplits;
> +		i = prandom_u32_max(nsplits);
>  		id = le32_to_cpu(fragtree->splits[i].frag);
>  		if (!__ceph_find_frag(ci, id))
>  			update = true;
> diff --git a/fs/ceph/mdsmap.c b/fs/ceph/mdsmap.c
> index 471bac335fae6..03b321f3459f1 100644
> --- a/fs/ceph/mdsmap.c
> +++ b/fs/ceph/mdsmap.c
> @@ -34,7 +34,7 @@ int ceph_mdsmap_get_random_mds(struct ceph_mdsmap *m)
>  		return -1;
>  
>  	/* pick */
> -	n = prandom_u32() % n;
> +	n = prandom_u32_max(n);
>  	for (j = 0, i = 0; i < m->m_num_mds; i++) {
>  		if (m->m_info[i].state > 0)
>  			j++;
> diff --git a/fs/ext2/ialloc.c b/fs/ext2/ialloc.c
> index fda7d3f5b4be5..6829910d14255 100644
> --- a/fs/ext2/ialloc.c
> +++ b/fs/ext2/ialloc.c
> @@ -281,8 +281,7 @@ static int find_group_orlov(struct super_block *sb, struct inode *parent)
>  		int best_ndir = inodes_per_group;
>  		int best_group = -1;
>  
> -		group = prandom_u32();
> -		parent_group = (unsigned)group % ngroups;
> +		parent_group = prandom_u32_max(ngroups);
>  		for (i = 0; i < ngroups; i++) {
>  			group = (parent_group + i) % ngroups;
>  			desc = ext2_get_group_desc (sb, group, NULL);
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 71e2b80ff4aae..eea9d4920bf78 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3183,8 +3183,8 @@ static int ext4_lazyinit_thread(void *arg)
>  			}
>  			if (!progress) {
>  				elr->lr_next_sched = jiffies +
> -					(prandom_u32()
> -					 % (EXT4_DEF_LI_MAX_START_DELAY * HZ));
> +				    prandom_u32_max(EXT4_DEF_LI_MAX_START_DELAY
> +						    * HZ);
>  			}
>  			if (time_before(elr->lr_next_sched, next_wakeup))
>  				next_wakeup = elr->lr_next_sched;
> @@ -3327,8 +3327,8 @@ static struct ext4_li_request *ext4_li_request_new(struct super_block *sb,
>  	 * spread the inode table initialization requests
>  	 * better.
>  	 */
> -	elr->lr_next_sched = jiffies + (prandom_u32() %
> -				(EXT4_DEF_LI_MAX_START_DELAY * HZ));
> +	elr->lr_next_sched = jiffies +
> +			prandom_u32_max(EXT4_DEF_LI_MAX_START_DELAY * HZ);
>  	return elr;
>  }
>  
> diff --git a/fs/ubifs/debug.c b/fs/ubifs/debug.c
> index 3d8d8eaea6c66..43ed46d488fd2 100644
> --- a/fs/ubifs/debug.c
> +++ b/fs/ubifs/debug.c
> @@ -2465,13 +2465,13 @@ static int power_cut_emulated(struct ubifs_info *c, int lnum, int write)
>  			if (chance(1, 2)) {
>  				d->pc_delay = 1;
>  				/* Fail within 1 minute */
> -				delay = prandom_u32() % 60000;
> +				delay = prandom_u32_max(60000);
>  				d->pc_timeout = jiffies;
>  				d->pc_timeout += msecs_to_jiffies(delay);
>  				ubifs_warn(c, "failing after %lums", delay);
>  			} else {
>  				d->pc_delay = 2;
> -				delay = prandom_u32() % 10000;
> +				delay = prandom_u32_max(10000);
>  				/* Fail within 10000 operations */
>  				d->pc_cnt_max = delay;
>  				ubifs_warn(c, "failing after %lu calls", delay);
> @@ -2551,7 +2551,7 @@ static int corrupt_data(const struct ubifs_info *c, const void *buf,
>  	unsigned int from, to, ffs = chance(1, 2);
>  	unsigned char *p = (void *)buf;
>  
> -	from = prandom_u32() % len;
> +	from = prandom_u32_max(len);
>  	/* Corruption span max to end of write unit */
>  	to = min(len, ALIGN(from + 1, c->max_write_size));
>  
> diff --git a/fs/ubifs/lpt_commit.c b/fs/ubifs/lpt_commit.c
> index ff5e0411cf2d1..29ba1bae1c366 100644
> --- a/fs/ubifs/lpt_commit.c
> +++ b/fs/ubifs/lpt_commit.c
> @@ -1977,21 +1977,21 @@ static int dbg_populate_lsave(struct ubifs_info *c)
>  		c->lsave[i] = c->main_first;
>  
>  	list_for_each_entry(lprops, &c->empty_list, list)
> -		c->lsave[prandom_u32() % c->lsave_cnt] = lprops->lnum;
> +		c->lsave[prandom_u32_max(c->lsave_cnt)] = lprops->lnum;
>  	list_for_each_entry(lprops, &c->freeable_list, list)
> -		c->lsave[prandom_u32() % c->lsave_cnt] = lprops->lnum;
> +		c->lsave[prandom_u32_max(c->lsave_cnt)] = lprops->lnum;
>  	list_for_each_entry(lprops, &c->frdi_idx_list, list)
> -		c->lsave[prandom_u32() % c->lsave_cnt] = lprops->lnum;
> +		c->lsave[prandom_u32_max(c->lsave_cnt)] = lprops->lnum;
>  
>  	heap = &c->lpt_heap[LPROPS_DIRTY_IDX - 1];
>  	for (i = 0; i < heap->cnt; i++)
> -		c->lsave[prandom_u32() % c->lsave_cnt] = heap->arr[i]->lnum;
> +		c->lsave[prandom_u32_max(c->lsave_cnt)] = heap->arr[i]->lnum;
>  	heap = &c->lpt_heap[LPROPS_DIRTY - 1];
>  	for (i = 0; i < heap->cnt; i++)
> -		c->lsave[prandom_u32() % c->lsave_cnt] = heap->arr[i]->lnum;
> +		c->lsave[prandom_u32_max(c->lsave_cnt)] = heap->arr[i]->lnum;
>  	heap = &c->lpt_heap[LPROPS_FREE - 1];
>  	for (i = 0; i < heap->cnt; i++)
> -		c->lsave[prandom_u32() % c->lsave_cnt] = heap->arr[i]->lnum;
> +		c->lsave[prandom_u32_max(c->lsave_cnt)] = heap->arr[i]->lnum;
>  
>  	return 1;
>  }
> diff --git a/fs/xfs/xfs_error.c b/fs/xfs/xfs_error.c
> index 331765afc53e4..ebb5f93a2381d 100644
> --- a/fs/xfs/xfs_error.c
> +++ b/fs/xfs/xfs_error.c
> @@ -252,7 +252,7 @@ xfs_errortag_test(
>  
>  	ASSERT(error_tag < XFS_ERRTAG_MAX);
>  	randfactor = mp->m_errortag[error_tag];
> -	if (!randfactor || prandom_u32() % randfactor)
> +	if (!randfactor || prandom_u32_max(randfactor))
>  		return false;
>  
>  	xfs_warn_ratelimited(mp,
> diff --git a/lib/find_bit_benchmark.c b/lib/find_bit_benchmark.c
> index 5637c5711db94..201b7c7881646 100644
> --- a/lib/find_bit_benchmark.c
> +++ b/lib/find_bit_benchmark.c
> @@ -137,8 +137,8 @@ static int __init find_bit_test(void)
>  	bitmap_zero(bitmap2, BITMAP_LEN);
>  
>  	while (nbits--) {
> -		__set_bit(prandom_u32() % BITMAP_LEN, bitmap);
> -		__set_bit(prandom_u32() % BITMAP_LEN, bitmap2);
> +		__set_bit(prandom_u32_max(BITMAP_LEN), bitmap);
> +		__set_bit(prandom_u32_max(BITMAP_LEN), bitmap2);
>  	}
>  
>  	test_find_next_bit(bitmap, BITMAP_LEN);
> diff --git a/lib/sbitmap.c b/lib/sbitmap.c
> index af88d1346dd74..ac5552dca4532 100644
> --- a/lib/sbitmap.c
> +++ b/lib/sbitmap.c
> @@ -367,7 +367,8 @@ int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
>  
>  	if (depth && !round_robin) {
>  		for_each_possible_cpu(i)
> -			*per_cpu_ptr(sbq->alloc_hint, i) = prandom_u32() % depth;
> +			*per_cpu_ptr(sbq->alloc_hint, i) =
> +							prandom_u32_max(depth);
>  	}
>  
>  	sbq->min_shallow_depth = UINT_MAX;
> @@ -426,7 +427,7 @@ int __sbitmap_queue_get(struct sbitmap_queue *sbq)
>  	hint = this_cpu_read(*sbq->alloc_hint);
>  	depth = READ_ONCE(sbq->sb.depth);
>  	if (unlikely(hint >= depth)) {
> -		hint = depth ? prandom_u32() % depth : 0;
> +		hint = depth ? prandom_u32_max(depth) : 0;
>  		this_cpu_write(*sbq->alloc_hint, hint);
>  	}
>  	nr = sbitmap_get(&sbq->sb, hint, sbq->round_robin);
> @@ -457,7 +458,7 @@ int __sbitmap_queue_get_shallow(struct sbitmap_queue *sbq,
>  	hint = this_cpu_read(*sbq->alloc_hint);
>  	depth = READ_ONCE(sbq->sb.depth);
>  	if (unlikely(hint >= depth)) {
> -		hint = depth ? prandom_u32() % depth : 0;
> +		hint = depth ? prandom_u32_max(depth) : 0;
>  		this_cpu_write(*sbq->alloc_hint, hint);
>  	}
>  	nr = sbitmap_get_shallow(&sbq->sb, hint, shallow_depth);
> diff --git a/lib/test_list_sort.c b/lib/test_list_sort.c
> index 1f017d3b610ee..7c8dbd653a7a9 100644
> --- a/lib/test_list_sort.c
> +++ b/lib/test_list_sort.c
> @@ -86,7 +86,7 @@ static int __init list_sort_test(void)
>  			goto exit;
>  
>  		 /* force some equivalencies */
> -		el->value = prandom_u32() % (TEST_LIST_LEN / 3);
> +		el->value = prandom_u32_max(TEST_LIST_LEN / 3);
>  		el->serial = i;
>  		el->poison1 = TEST_POISON1;
>  		el->poison2 = TEST_POISON2;
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index bb3261d45b6a3..efe7d972fdde3 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -3204,7 +3204,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>  		 * select a random position to start with to help wear leveling
>  		 * SSD
>  		 */
> -		p->cluster_next = 1 + (prandom_u32() % p->highest_bit);
> +		p->cluster_next = 1 + prandom_u32_max(p->highest_bit);
>  		nr_cluster = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
>  
>  		cluster_info = kvcalloc(nr_cluster, sizeof(*cluster_info),
> diff --git a/net/batman-adv/bat_iv_ogm.c b/net/batman-adv/bat_iv_ogm.c
> index d88a4de022372..46c5cd9f8019e 100644
> --- a/net/batman-adv/bat_iv_ogm.c
> +++ b/net/batman-adv/bat_iv_ogm.c
> @@ -280,7 +280,7 @@ batadv_iv_ogm_emit_send_time(const struct batadv_priv *bat_priv)
>  	unsigned int msecs;
>  
>  	msecs = atomic_read(&bat_priv->orig_interval) - BATADV_JITTER;
> -	msecs += prandom_u32() % (2 * BATADV_JITTER);
> +	msecs += prandom_u32_max(2 * BATADV_JITTER);
>  
>  	return jiffies + msecs_to_jiffies(msecs);
>  }
> diff --git a/net/batman-adv/bat_v_elp.c b/net/batman-adv/bat_v_elp.c
> index 2614a9caee008..13c6f5150dc00 100644
> --- a/net/batman-adv/bat_v_elp.c
> +++ b/net/batman-adv/bat_v_elp.c
> @@ -49,7 +49,7 @@ static void batadv_v_elp_start_timer(struct batadv_hard_iface *hard_iface)
>  	unsigned int msecs;
>  
>  	msecs = atomic_read(&hard_iface->bat_v.elp_interval) - BATADV_JITTER;
> -	msecs += prandom_u32() % (2 * BATADV_JITTER);
> +	msecs += prandom_u32_max(2 * BATADV_JITTER);
>  
>  	queue_delayed_work(batadv_event_workqueue, &hard_iface->bat_v.elp_wq,
>  			   msecs_to_jiffies(msecs));
> diff --git a/net/batman-adv/bat_v_ogm.c b/net/batman-adv/bat_v_ogm.c
> index 714ce56cfcc82..411ce5fc6492f 100644
> --- a/net/batman-adv/bat_v_ogm.c
> +++ b/net/batman-adv/bat_v_ogm.c
> @@ -107,7 +107,7 @@ static void batadv_v_ogm_start_timer(struct batadv_priv *bat_priv)
>  		return;
>  
>  	msecs = atomic_read(&bat_priv->orig_interval) - BATADV_JITTER;
> -	msecs += prandom_u32() % (2 * BATADV_JITTER);
> +	msecs += prandom_u32_max(2 * BATADV_JITTER);
>  	queue_delayed_work(batadv_event_workqueue, &bat_priv->bat_v.ogm_wq,
>  			   msecs_to_jiffies(msecs));
>  }
> diff --git a/net/ceph/mon_client.c b/net/ceph/mon_client.c
> index 9d9e4e4ea600e..b5db5c05843cf 100644
> --- a/net/ceph/mon_client.c
> +++ b/net/ceph/mon_client.c
> @@ -155,7 +155,7 @@ static void pick_new_mon(struct ceph_mon_client *monc)
>  				max--;
>  		}
>  
> -		n = prandom_u32() % max;
> +		n = prandom_u32_max(max);
>  		if (o >= 0 && n >= o)
>  			n++;
>  
> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> index 789a73aa7bd87..cc00feb89f7f8 100644
> --- a/net/core/neighbour.c
> +++ b/net/core/neighbour.c
> @@ -112,7 +112,7 @@ static void neigh_cleanup_and_release(struct neighbour *neigh)
>  
>  unsigned long neigh_rand_reach_time(unsigned long base)
>  {
> -	return base ? (prandom_u32() % base) + (base >> 1) : 0;
> +	return base ? prandom_u32_max(base) + (base >> 1) : 0;
>  }
>  EXPORT_SYMBOL(neigh_rand_reach_time);
>  
> @@ -1567,8 +1567,8 @@ void pneigh_enqueue(struct neigh_table *tbl, struct neigh_parms *p,
>  {
>  	unsigned long now = jiffies;
>  
> -	unsigned long sched_next = now + (prandom_u32() %
> -					  NEIGH_VAR(p, PROXY_DELAY));
> +	unsigned long sched_next = now +
> +			prandom_u32_max(NEIGH_VAR(p, PROXY_DELAY));
>  
>  	if (tbl->proxy_queue.qlen > NEIGH_VAR(p, PROXY_QLEN)) {
>  		kfree_skb(skb);
> diff --git a/net/core/pktgen.c b/net/core/pktgen.c
> index 294bfcf0ce0eb..f2b6460bd88cc 100644
> --- a/net/core/pktgen.c
> +++ b/net/core/pktgen.c
> @@ -2216,7 +2216,7 @@ static inline int f_pick(struct pktgen_dev *pkt_dev)
>  				pkt_dev->curfl = 0; /*reset */
>  		}
>  	} else {
> -		flow = prandom_u32() % pkt_dev->cflows;
> +		flow = prandom_u32_max(pkt_dev->cflows);
>  		pkt_dev->curfl = flow;
>  
>  		if (pkt_dev->flows[flow].count > pkt_dev->lflow) {
> @@ -2272,7 +2272,7 @@ static void set_cur_queue_map(struct pktgen_dev *pkt_dev)
>  	else if (pkt_dev->queue_map_min <= pkt_dev->queue_map_max) {
>  		__u16 t;
>  		if (pkt_dev->flags & F_QUEUE_MAP_RND) {
> -			t = prandom_u32() %
> +			t = prandom_u32_max
>  				(pkt_dev->queue_map_max -
>  				 pkt_dev->queue_map_min + 1)
>  				+ pkt_dev->queue_map_min;
> @@ -2304,7 +2304,7 @@ static void mod_cur_headers(struct pktgen_dev *pkt_dev)
>  		__u32 tmp;
>  
>  		if (pkt_dev->flags & F_MACSRC_RND)
> -			mc = prandom_u32() % pkt_dev->src_mac_count;
> +			mc = prandom_u32_max(pkt_dev->src_mac_count);
>  		else {
>  			mc = pkt_dev->cur_src_mac_offset++;
>  			if (pkt_dev->cur_src_mac_offset >=
> @@ -2330,7 +2330,7 @@ static void mod_cur_headers(struct pktgen_dev *pkt_dev)
>  		__u32 tmp;
>  
>  		if (pkt_dev->flags & F_MACDST_RND)
> -			mc = prandom_u32() % pkt_dev->dst_mac_count;
> +			mc = prandom_u32_max(pkt_dev->dst_mac_count);
>  
>  		else {
>  			mc = pkt_dev->cur_dst_mac_offset++;
> @@ -2371,7 +2371,7 @@ static void mod_cur_headers(struct pktgen_dev *pkt_dev)
>  
>  	if (pkt_dev->udp_src_min < pkt_dev->udp_src_max) {
>  		if (pkt_dev->flags & F_UDPSRC_RND)
> -			pkt_dev->cur_udp_src = prandom_u32() %
> +			pkt_dev->cur_udp_src = prandom_u32_max
>  				(pkt_dev->udp_src_max - pkt_dev->udp_src_min)
>  				+ pkt_dev->udp_src_min;
>  
> @@ -2384,7 +2384,7 @@ static void mod_cur_headers(struct pktgen_dev *pkt_dev)
>  
>  	if (pkt_dev->udp_dst_min < pkt_dev->udp_dst_max) {
>  		if (pkt_dev->flags & F_UDPDST_RND) {
> -			pkt_dev->cur_udp_dst = prandom_u32() %
> +			pkt_dev->cur_udp_dst = prandom_u32_max
>  				(pkt_dev->udp_dst_max - pkt_dev->udp_dst_min)
>  				+ pkt_dev->udp_dst_min;
>  		} else {
> @@ -2401,7 +2401,7 @@ static void mod_cur_headers(struct pktgen_dev *pkt_dev)
>  		if (imn < imx) {
>  			__u32 t;
>  			if (pkt_dev->flags & F_IPSRC_RND)
> -				t = prandom_u32() % (imx - imn) + imn;
> +				t = prandom_u32_max(imx - imn) + imn;
>  			else {
>  				t = ntohl(pkt_dev->cur_saddr);
>  				t++;
> @@ -2423,8 +2423,8 @@ static void mod_cur_headers(struct pktgen_dev *pkt_dev)
>  				if (pkt_dev->flags & F_IPDST_RND) {
>  
>  					do {
> -						t = prandom_u32() %
> -							(imx - imn) + imn;
> +						t = prandom_u32_max(imx - imn) +
> +						       imn;
>  						s = htonl(t);
>  					} while (ipv4_is_loopback(s) ||
>  						ipv4_is_multicast(s) ||
> @@ -2471,7 +2471,7 @@ static void mod_cur_headers(struct pktgen_dev *pkt_dev)
>  	if (pkt_dev->min_pkt_size < pkt_dev->max_pkt_size) {
>  		__u32 t;
>  		if (pkt_dev->flags & F_TXSIZE_RND) {
> -			t = prandom_u32() %
> +			t = prandom_u32_max
>  				(pkt_dev->max_pkt_size - pkt_dev->min_pkt_size)
>  				+ pkt_dev->min_pkt_size;
>  		} else {
> diff --git a/net/core/stream.c b/net/core/stream.c
> index 4f1d4aa5fb38d..cf9b67c5b39ca 100644
> --- a/net/core/stream.c
> +++ b/net/core/stream.c
> @@ -123,7 +123,7 @@ int sk_stream_wait_memory(struct sock *sk, long *timeo_p)
>  	DEFINE_WAIT_FUNC(wait, woken_wake_function);
>  
>  	if (sk_stream_memory_free(sk))
> -		current_timeo = vm_wait = (prandom_u32() % (HZ / 5)) + 2;
> +		current_timeo = vm_wait = prandom_u32_max(HZ / 5) + 2;
>  
>  	add_wait_queue(sk_sleep(sk), &wait);
>  
> diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
> index 3b9c7a2725a99..8c429dd3aabc4 100644
> --- a/net/ipv4/igmp.c
> +++ b/net/ipv4/igmp.c
> @@ -215,7 +215,7 @@ static void igmp_stop_timer(struct ip_mc_list *im)
>  /* It must be called with locked im->lock */
>  static void igmp_start_timer(struct ip_mc_list *im, int max_delay)
>  {
> -	int tv = prandom_u32() % max_delay;
> +	int tv = prandom_u32_max(max_delay);
>  
>  	im->tm_running = 1;
>  	if (!mod_timer(&im->timer, jiffies+tv+2))
> @@ -224,7 +224,7 @@ static void igmp_start_timer(struct ip_mc_list *im, int max_delay)
>  
>  static void igmp_gq_start_timer(struct in_device *in_dev)
>  {
> -	int tv = prandom_u32() % in_dev->mr_maxdelay;
> +	int tv = prandom_u32_max(in_dev->mr_maxdelay);
>  	unsigned long exp = jiffies + tv + 2;
>  
>  	if (in_dev->mr_gq_running &&
> @@ -238,7 +238,7 @@ static void igmp_gq_start_timer(struct in_device *in_dev)
>  
>  static void igmp_ifc_start_timer(struct in_device *in_dev, int delay)
>  {
> -	int tv = prandom_u32() % delay;
> +	int tv = prandom_u32_max(delay);
>  
>  	if (!mod_timer(&in_dev->mr_ifc_timer, jiffies+tv+2))
>  		in_dev_hold(in_dev);
> diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> index 159513ce85114..4d59bbab0ac5a 100644
> --- a/net/ipv4/inet_connection_sock.c
> +++ b/net/ipv4/inet_connection_sock.c
> @@ -200,7 +200,7 @@ inet_csk_find_open_port(struct sock *sk, struct inet_bind_bucket **tb_ret, int *
>  	if (likely(remaining > 1))
>  		remaining &= ~1U;
>  
> -	offset = prandom_u32() % remaining;
> +	offset = prandom_u32_max(remaining);
>  	/* __inet_hash_connect() favors ports having @low parity
>  	 * We do the opposite to not pollute connect() users.
>  	 */
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 46d614b611db2..ec3f472bc5a8f 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -3921,7 +3921,7 @@ static void addrconf_dad_kick(struct inet6_ifaddr *ifp)
>  	if (ifp->flags & IFA_F_OPTIMISTIC)
>  		rand_num = 0;
>  	else
> -		rand_num = prandom_u32() % (idev->cnf.rtr_solicit_delay ? : 1);
> +		rand_num = prandom_u32_max(idev->cnf.rtr_solicit_delay ? : 1);
>  
>  	nonce = 0;
>  	if (idev->cnf.enhanced_dad ||
> diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
> index eaa4c2cc2fbb2..e0b5810c3d7fe 100644
> --- a/net/ipv6/mcast.c
> +++ b/net/ipv6/mcast.c
> @@ -1032,7 +1032,7 @@ bool ipv6_chk_mcast_addr(struct net_device *dev, const struct in6_addr *group,
>  
>  static void mld_gq_start_timer(struct inet6_dev *idev)
>  {
> -	unsigned long tv = prandom_u32() % idev->mc_maxdelay;
> +	unsigned long tv = prandom_u32_max(idev->mc_maxdelay);
>  
>  	idev->mc_gq_running = 1;
>  	if (!mod_timer(&idev->mc_gq_timer, jiffies+tv+2))
> @@ -1048,7 +1048,7 @@ static void mld_gq_stop_timer(struct inet6_dev *idev)
>  
>  static void mld_ifc_start_timer(struct inet6_dev *idev, unsigned long delay)
>  {
> -	unsigned long tv = prandom_u32() % delay;
> +	unsigned long tv = prandom_u32_max(delay);
>  
>  	if (!mod_timer(&idev->mc_ifc_timer, jiffies+tv+2))
>  		in6_dev_hold(idev);
> @@ -1063,7 +1063,7 @@ static void mld_ifc_stop_timer(struct inet6_dev *idev)
>  
>  static void mld_dad_start_timer(struct inet6_dev *idev, unsigned long delay)
>  {
> -	unsigned long tv = prandom_u32() % delay;
> +	unsigned long tv = prandom_u32_max(delay);
>  
>  	if (!mod_timer(&idev->mc_dad_timer, jiffies+tv+2))
>  		in6_dev_hold(idev);
> @@ -1094,7 +1094,7 @@ static void igmp6_group_queried(struct ifmcaddr6 *ma, unsigned long resptime)
>  	}
>  
>  	if (delay >= resptime)
> -		delay = prandom_u32() % resptime;
> +		delay = prandom_u32_max(resptime);
>  
>  	ma->mca_timer.expires = jiffies + delay;
>  	if (!mod_timer(&ma->mca_timer, jiffies + delay))
> @@ -2416,7 +2416,7 @@ static void igmp6_join_group(struct ifmcaddr6 *ma)
>  
>  	igmp6_send(&ma->mca_addr, ma->idev->dev, ICMPV6_MGM_REPORT);
>  
> -	delay = prandom_u32() % unsolicited_report_interval(ma->idev);
> +	delay = prandom_u32_max(unsolicited_report_interval(ma->idev));
>  
>  	spin_lock_bh(&ma->mca_lock);
>  	if (del_timer(&ma->mca_timer)) {
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index 20edb7c25e221..9068e0b13e0be 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -1305,7 +1305,7 @@ static bool fanout_flow_is_huge(struct packet_sock *po, struct sk_buff *skb)
>  		if (READ_ONCE(history[i]) == rxhash)
>  			count++;
>  
> -	victim = prandom_u32() % ROLLOVER_HLEN;
> +	victim = prandom_u32_max(ROLLOVER_HLEN);
>  
>  	/* Avoid dirtying the cache line if possible */
>  	if (READ_ONCE(history[victim]) != rxhash)
> diff --git a/net/sched/act_gact.c b/net/sched/act_gact.c
> index 4160657727196..56afdde2bc558 100644
> --- a/net/sched/act_gact.c
> +++ b/net/sched/act_gact.c
> @@ -26,7 +26,7 @@ static struct tc_action_ops act_gact_ops;
>  static int gact_net_rand(struct tcf_gact *gact)
>  {
>  	smp_rmb(); /* coupled with smp_wmb() in tcf_gact_init() */
> -	if (prandom_u32() % gact->tcfg_pval)
> +	if (prandom_u32_max(gact->tcfg_pval))
>  		return gact->tcf_action;
>  	return gact->tcfg_paction;
>  }
> diff --git a/net/sched/act_sample.c b/net/sched/act_sample.c
> index ce948c1e24dc5..41701acc490e6 100644
> --- a/net/sched/act_sample.c
> +++ b/net/sched/act_sample.c
> @@ -172,7 +172,7 @@ static int tcf_sample_act(struct sk_buff *skb, const struct tc_action *a,
>  	psample_group = rcu_dereference_bh(s->psample_group);
>  
>  	/* randomly sample packets according to rate */
> -	if (psample_group && (prandom_u32() % s->rate == 0)) {
> +	if (psample_group && prandom_u32_max(s->rate) == 0) {
>  		if (!skb_at_tc_ingress(skb)) {
>  			iif = skb->skb_iif;
>  			oif = skb->dev->ifindex;
> diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
> index 42e557d48e4e3..7b7503326faf5 100644
> --- a/net/sched/sch_netem.c
> +++ b/net/sched/sch_netem.c
> @@ -513,7 +513,7 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
>  			goto finish_segs;
>  		}
>  
> -		skb->data[prandom_u32() % skb_headlen(skb)] ^=
> +		skb->data[prandom_u32_max(skb_headlen(skb))] ^=
>  			1<<(prandom_u32() % 8);
>  	}
>  
> @@ -632,9 +632,8 @@ static void get_slot_next(struct netem_sched_data *q, u64 now)
>  
>  	if (!q->slot_dist)
>  		next_delay = q->slot_config.min_delay +
> -				(prandom_u32() *
> -				 (q->slot_config.max_delay -
> -				  q->slot_config.min_delay) >> 32);
> +			prandom_u32_max(q->slot_config.max_delay -
> +					q->slot_config.min_delay);
>  	else
>  		next_delay = tabledist(q->slot_config.dist_delay,
>  				       (s32)(q->slot_config.dist_jitter),
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index 0b485952a71c1..7acb374ed8596 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -8286,7 +8286,7 @@ static int sctp_get_port_local(struct sock *sk, union sctp_addr *addr)
>  
>  		inet_get_local_port_range(net, &low, &high);
>  		remaining = (high - low) + 1;
> -		rover = prandom_u32() % remaining + low;
> +		rover = prandom_u32_max(remaining) + low;
>  
>  		do {
>  			rover++;
> diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> index d86c664ea6afc..f90727d0a9c48 100644
> --- a/net/sunrpc/xprtsock.c
> +++ b/net/sunrpc/xprtsock.c
> @@ -1699,7 +1699,7 @@ static int xs_get_random_port(void)
>  	if (max < min)
>  		return -EADDRINUSE;
>  	range = max - min + 1;
> -	rand = (unsigned short) prandom_u32() % range;
> +	rand = (unsigned short) prandom_u32_max(range);
>  	return rand + min;
>  }
>  
> diff --git a/net/tipc/socket.c b/net/tipc/socket.c
> index 693e8902161ef..1118e6815256c 100644
> --- a/net/tipc/socket.c
> +++ b/net/tipc/socket.c
> @@ -2151,8 +2151,7 @@ static bool tipc_sk_filter_connect(struct tipc_sock *tsk, struct sk_buff *skb)
>  		/* Prepare for new setup attempt if we have a SYN clone */
>  		if (skb_queue_empty(&sk->sk_write_queue))
>  			break;
> -		get_random_bytes(&delay, 2);
> -		delay %= (tsk->conn_timeout / 4);
> +		delay = get_random_max(tsk->conn_timeout / 4);
>  		delay = msecs_to_jiffies(delay + 100);
>  		sk_reset_timer(sk, &sk->sk_timer, jiffies + delay);
>  		return false;
> @@ -2917,7 +2916,7 @@ static int tipc_sk_insert(struct tipc_sock *tsk)
>  	struct net *net = sock_net(sk);
>  	struct tipc_net *tn = net_generic(net, tipc_net_id);
>  	u32 remaining = (TIPC_MAX_PORT - TIPC_MIN_PORT) + 1;
> -	u32 portid = prandom_u32() % remaining + TIPC_MIN_PORT;
> +	u32 portid = prandom_u32_max(remaining) + TIPC_MIN_PORT;
>  
>  	while (remaining--) {
>  		portid++;
> diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
> index f3423562d9336..342d4fabc722e 100644
> --- a/net/xfrm/xfrm_state.c
> +++ b/net/xfrm/xfrm_state.c
> @@ -1991,7 +1991,7 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high)
>  	} else {
>  		u32 spi = 0;
>  		for (h = 0; h < high-low+1; h++) {
> -			spi = low + prandom_u32()%(high-low+1);
> +			spi = low + prandom_u32_max(high-low+1);
>  			x0 = xfrm_state_lookup(net, mark, &x->id.daddr, htonl(spi), x->id.proto, x->props.family);
>  			if (x0 == NULL) {
>  				x->id.spi = htonl(spi);
> -- 
> 2.26.0
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR

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