On Oct 19, 2021 / 06:08, Jens Axboe wrote:
> If we have just one queue type in the plug list, then we can extend our
> direct issue to cover a full plug list as well.
>
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Hi Jens, I tried out for-next branch and observed A WARNING "do not call
blocking ops when !TASK_RUNNING" [1]. Reverting this patch from the for-next
branch, the warning disappears. The warning was triggered when mkfs.xfs is
run for memory backed null_blk devices with "none" scheduler. The commands below
recreates it.
# modprobe null_blk nr_devices=0
# mkdir /sys/kernel/config/nullb/nullb0
# declare sysfs=/sys/kernel/config/nullb/nullb0
# echo 1 > "${sysfs}"/memory_backed
# echo 1 > "${sysfs}"/power
# echo none > /sys/block/nullb0/queue/scheduler
# mkfs.xfs /dev/nullb0
Referring the call stack printed, I walked through the function calls. In
__blkdev_direct_IO_simple(), task state is set UNINTERRUPTIBLE. Way
down to might_sleep_if() called from null_queue_rq(), it is warned that
the task state is not RUNNING. This patch adds blk_mq_plug_issue_direct()
call in blk_mq_flush_plug_list(), then the call path was linked from
__blkdev_direct_IO_simple() to null_queue_rq().
__blkdev_direct_IO_simple() block/fops.c
set_current_state(TASK_UNINTERRUPTIBLE) ... current->__state = TASK_UNINTERRUPTIBLE
blk_io_schedule()
io_schedule_timeout() kernel/sched/core.c
io_schedule_prepare()
blk_schedule_flush_plug() include/linux/blkdev.h
blk_flush_plug_list() block/blk-core.c
blk_mq_flush_plug_list()
blk_mq_flush_plug_list() block/blk-mq.c ... this patch added call to blk_mq_plug_issue_direct()
blk_mq_plug_issue_direct()
blk_mq_reqeust_issue_directly()
__blk_mq_try_issue_directly()
__blk_mq_issue_directly()
q->mq_ops->queue_rq()
null_queue_rq() drivers/block/null_blk/main.c
might_sleep_if(flags & BLK_MQ_F_BLOCKING) include/linux/kernel.h
might_sleep()
__might_sleep() kernel/sched/core.c ... current->__state != TASK_RUNNING (WARN_ONCE)
So far, I can't think of a good solution for this warning. Any idea?
[1]
[60501.340746] null_blk: module loaded
[60519.303106] ------------[ cut here ]------------
[60519.308485] do not call blocking ops when !TASK_RUNNING; state=2 set at [<000000005ba5e596>] __blkdev_direct_IO_simple+0x3f8/0x6f0
[60519.320943] WARNING: CPU: 2 PID: 8929 at kernel/sched/core.c:9486 __might_sleep+0x124/0x160
[60519.330001] Modules linked in: null_blk xfs dm_zoned xt_conntrack nf_nat_tftp nf_conntrack_tftp bridge stp llc nft_objref nf_conntrack_netbios_ns nf_conntrack_broadcast nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_tables ebtable_nat ebtable_broute ip6table_nat ip6table_mangle ip6table_raw ip6table_security iptable_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 iptable_mangle iptable_raw iptable_security ip_set nfnetlink ebtable_filter rfkill ebtables target_core_user target_core_mod ip6table_filter ip6_tables iptable_filter sunrpc intel_rapl_msr intel_rapl_common x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel kvm irqbypass iTCO_wdt intel_pmc_bxt iTCO_vendor_support rapl intel_cstate intel_uncore pcspkr joydev ipmi_ssif i2c_i801 lpc_ich i2c_smbus ses enclosure mei_me mei ioatdma wmi acpi_ipmi ipmi_si ipmi_devintf ipmi_msghandler acpi_pad acpi_power_meter zram ip_tables ast
[60519.330166] drm_vram_helper drm_kms_helper cec drm_ttm_helper crct10dif_pclmul ttm crc32_pclmul crc32c_intel drm ghash_clmulni_intel igb mpt3sas nvme dca nvme_core i2c_algo_bit raid_class scsi_transport_sas fuse [last unloaded: null_blk]
[60519.438458] CPU: 2 PID: 8929 Comm: mkfs.xfs Not tainted 5.15.0-rc6+ #11
[60519.445781] Hardware name: Supermicro Super Server/X10SRL-F, BIOS 2.0 12/17/2015
[60519.453893] RIP: 0010:__might_sleep+0x124/0x160
[60519.459139] Code: 48 8d bb 98 2c 00 00 48 89 fa 48 c1 ea 03 80 3c 02 00 75 31 48 8b 93 98 2c 00 00 44 89 f6 48 c7 c7 e0 f2 88 8a e8 04 eb f9 01 <0f> 0b e9 6d ff ff ff e8 60 d1 66 00 e9 1c ff ff ff e8 66 d1 66 00
[60519.478594] RSP: 0018:ffff8882707ef5a8 EFLAGS: 00010286
[60519.484533] RAX: 0000000000000000 RBX: ffff888125cbb280 RCX: 0000000000000000
[60519.492379] RDX: 0000000000000004 RSI: 0000000000000008 RDI: ffffed104e0fdeab
[60519.500216] RBP: ffffffffc16122c0 R08: 0000000000000001 R09: ffff8888114ad587
[60519.508052] R10: ffffed1102295ab0 R11: 0000000000000001 R12: 0000000000000618
[60519.515886] R13: 0000000000000000 R14: 0000000000000002 R15: ffff88813160a000
[60519.523721] FS: 00007fd79959b400(0000) GS:ffff888811480000(0000) knlGS:0000000000000000
[60519.532509] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[60519.538963] CR2: 000055bf4e3dc000 CR3: 000000029e904005 CR4: 00000000001706e0
[60519.546803] Call Trace:
[60519.549976] null_queue_rq+0x3ee/0x6b0 [null_blk]
[60519.555407] __blk_mq_try_issue_directly+0x433/0x680
[60519.561085] ? __submit_bio+0x63a/0x780
[60519.565636] ? __blk_mq_get_driver_tag+0x9a0/0x9a0
[60519.571144] blk_mq_flush_plug_list+0x5f6/0xc40
[60519.576387] ? iov_iter_get_pages_alloc+0xf50/0xf50
[60519.581980] ? find_held_lock+0x2c/0x110
[60519.586618] ? blk_mq_insert_requests+0x440/0x440
[60519.592044] ? __blkdev_direct_IO_simple+0x3f8/0x6f0
[60519.597719] blk_flush_plug_list+0x28f/0x410
[60519.602710] ? blk_start_plug_nr_ios+0x270/0x270
[60519.608039] ? __blkdev_direct_IO_simple+0x3f8/0x6f0
[60519.613713] io_schedule_timeout+0xcc/0x150
[60519.618621] __blkdev_direct_IO_simple+0x475/0x6f0
[60519.624126] ? blkdev_llseek+0xc0/0xc0
[60519.628598] ? blkdev_get_block+0xd0/0xd0
[60519.633320] ? filemap_check_errors+0xe0/0xe0
[60519.638391] ? find_held_lock+0x2c/0x110
[60519.643024] ? lock_release+0x1d4/0x690
[60519.647574] blkdev_direct_IO+0x9b2/0x1110
[60519.652389] ? filemap_check_errors+0x56/0xe0
[60519.657455] ? add_watch_to_object+0xa0/0x6e0
[60519.662524] ? blkdev_bio_end_io+0x490/0x490
[60519.667518] generic_file_direct_write+0x1a9/0x4a0
[60519.673026] __generic_file_write_iter+0x1fa/0x480
[60519.678526] ? lock_is_held_type+0xe0/0x110
[60519.683420] blkdev_write_iter+0x319/0x5a0
[60519.688231] ? blkdev_open+0x260/0x260
[60519.692690] ? lock_downgrade+0x6b0/0x6b0
[60519.697412] ? do_raw_spin_unlock+0x55/0x1f0
[60519.702392] new_sync_write+0x359/0x5e0
[60519.706941] ? new_sync_read+0x5d0/0x5d0
[60519.711582] ? __cond_resched+0x15/0x30
[60519.716124] ? inode_security+0x56/0xf0
[60519.720688] vfs_write+0x5e4/0x8e0
[60519.724805] __x64_sys_pwrite64+0x17c/0x1d0
[60519.729698] ? vfs_write+0x8e0/0x8e0
[60519.733982] ? syscall_enter_from_user_mode+0x21/0x70
[60519.739747] do_syscall_64+0x3b/0x90
[60519.744037] entry_SYSCALL_64_after_hwframe+0x44/0xae
[60519.749796] RIP: 0033:0x7fd7997c125a
[60519.754088] Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb ba 0f 1f 00 f3 0f 1e fa 49 89 ca 64 8b 04 25 18 00 00 00 85 c0 75 15 b8 12 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 5e c3 0f 1f 44 00 00 48 83 ec 28 48 89 54 24
[60519.773543] RSP: 002b:00007ffe8d456718 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
[60519.781816] RAX: ffffffffffffffda RBX: 00007ffe8d456e10 RCX: 00007fd7997c125a
[60519.789656] RDX: 0000000000020000 RSI: 000055bf4e3bd600 RDI: 0000000000000004
[60519.797494] RBP: 0000000000020000 R08: 000055bf4e3bd600 R09: 00007fd79975fa60
[60519.805333] R10: 00000003fffe0000 R11: 0000000000000246 R12: 000055bf4e3b9710
[60519.813172] R13: 0000000000000004 R14: 000055bf4e3bd600 R15: 0000000000001000
[60519.821028] irq event stamp: 20385
[60519.825139] hardirqs last enabled at (20395): [<ffffffff883481e0>] __up_console_sem+0x60/0x70
[60519.834455] hardirqs last disabled at (20404): [<ffffffff883481c5>] __up_console_sem+0x45/0x70
[60519.843763] softirqs last enabled at (20372): [<ffffffff881e6a7c>] __irq_exit_rcu+0x19c/0x200
[60519.853079] softirqs last disabled at (20367): [<ffffffff881e6a7c>] __irq_exit_rcu+0x19c/0x200
[60519.862389] ---[ end trace be9623465002e439 ]---
--
Best Regards,
Shin'ichiro Kawasaki
> ---
> block/blk-core.c | 1 +
> block/blk-mq.c | 60 ++++++++++++++++++++++++++++++++++++++++++
> include/linux/blkdev.h | 1 +
> 3 files changed, 62 insertions(+)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 14d20909f61a..e6ad5b51d0c3 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1555,6 +1555,7 @@ void blk_start_plug_nr_ios(struct blk_plug *plug, unsigned short nr_ios)
> plug->nr_ios = min_t(unsigned short, nr_ios, BLK_MAX_REQUEST_COUNT);
> plug->rq_count = 0;
> plug->multiple_queues = false;
> + plug->has_elevator = false;
> plug->nowait = false;
> INIT_LIST_HEAD(&plug->cb_list);
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 620233b85af2..d0fe86b46d1b 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -2147,6 +2147,58 @@ void blk_mq_insert_requests(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
> spin_unlock(&ctx->lock);
> }
>
> +static void blk_mq_commit_rqs(struct blk_mq_hw_ctx *hctx, int *queued,
> + bool from_schedule)
> +{
> + if (hctx->queue->mq_ops->commit_rqs) {
> + trace_block_unplug(hctx->queue, *queued, !from_schedule);
> + hctx->queue->mq_ops->commit_rqs(hctx);
> + }
> + *queued = 0;
> +}
> +
> +static void blk_mq_plug_issue_direct(struct blk_plug *plug, bool from_schedule)
> +{
> + struct blk_mq_hw_ctx *hctx = NULL;
> + struct request *rq;
> + int queued = 0;
> + int errors = 0;
> +
> + while ((rq = rq_list_pop(&plug->mq_list))) {
> + bool last = rq_list_empty(plug->mq_list);
> + blk_status_t ret;
> +
> + if (hctx != rq->mq_hctx) {
> + if (hctx)
> + blk_mq_commit_rqs(hctx, &queued, from_schedule);
> + hctx = rq->mq_hctx;
> + }
> +
> + ret = blk_mq_request_issue_directly(rq, last);
> + switch (ret) {
> + case BLK_STS_OK:
> + queued++;
> + break;
> + case BLK_STS_RESOURCE:
> + case BLK_STS_DEV_RESOURCE:
> + blk_mq_request_bypass_insert(rq, false, last);
> + blk_mq_commit_rqs(hctx, &queued, from_schedule);
> + return;
> + default:
> + blk_mq_end_request(rq, ret);
> + errors++;
> + break;
> + }
> + }
> +
> + /*
> + * If we didn't flush the entire list, we could have told the driver
> + * there was more coming, but that turned out to be a lie.
> + */
> + if (errors)
> + blk_mq_commit_rqs(hctx, &queued, from_schedule);
> +}
> +
> void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
> {
> struct blk_mq_hw_ctx *this_hctx;
> @@ -2158,6 +2210,12 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
> return;
> plug->rq_count = 0;
>
> + if (!plug->multiple_queues && !plug->has_elevator) {
> + blk_mq_plug_issue_direct(plug, from_schedule);
> + if (rq_list_empty(plug->mq_list))
> + return;
> + }
> +
> this_hctx = NULL;
> this_ctx = NULL;
> depth = 0;
> @@ -2374,6 +2432,8 @@ static void blk_add_rq_to_plug(struct blk_plug *plug, struct request *rq)
> if (nxt && nxt->q != rq->q)
> plug->multiple_queues = true;
> }
> + if (!plug->has_elevator && (rq->rq_flags & RQF_ELV))
> + plug->has_elevator = true;
> rq->rq_next = NULL;
> rq_list_add(&plug->mq_list, rq);
> plug->rq_count++;
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 80668e316eea..2e93682f8f68 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -720,6 +720,7 @@ struct blk_plug {
> unsigned short rq_count;
>
> bool multiple_queues;
> + bool has_elevator;
> bool nowait;
>
> struct list_head cb_list; /* md requires an unplug callback */
> --
> 2.33.1
>
