From: Roman Gushchin <guro@xxxxxx> Subject: writeback, cgroup: do not reparent dax inodes The inode switching code is not suited for dax inodes. An attempt to switch a dax inode to a parent writeback structure (as a part of a writeback cleanup procedure) results in a panic like this: [ 987.071651] run fstests generic/270 at 2021-07-15 05:54:02 [ 988.704940] XFS (pmem0p2): EXPERIMENTAL big timestamp feature in use. Use at your own risk! [ 988.746847] XFS (pmem0p2): DAX enabled. Warning: EXPERIMENTAL, use at your own risk [ 988.786070] XFS (pmem0p2): EXPERIMENTAL inode btree counters feature in use. Use at your own risk! [ 988.828639] XFS (pmem0p2): Mounting V5 Filesystem [ 988.854019] XFS (pmem0p2): Ending clean mount [ 988.874550] XFS (pmem0p2): Quotacheck needed: Please wait. [ 988.900618] XFS (pmem0p2): Quotacheck: Done. [ 989.090783] XFS (pmem0p2): xlog_verify_grant_tail: space > BBTOB(tail_blocks) [ 989.092751] XFS (pmem0p2): xlog_verify_grant_tail: space > BBTOB(tail_blocks) [ 989.092962] XFS (pmem0p2): xlog_verify_grant_tail: space > BBTOB(tail_blocks) [ 1010.105586] BUG: unable to handle page fault for address: 0000000005b0f669 [ 1010.141817] #PF: supervisor read access in kernel mode [ 1010.167824] #PF: error_code(0x0000) - not-present page [ 1010.191499] PGD 0 P4D 0 [ 1010.203346] Oops: 0000 [#1] SMP PTI [ 1010.219596] CPU: 13 PID: 10479 Comm: kworker/13:16 Not tainted 5.14.0-rc1-master-8096acd7442e+ #8 [ 1010.260441] Hardware name: HP ProLiant DL360 Gen9/ProLiant DL360 Gen9, BIOS P89 09/13/2016 [ 1010.297792] Workqueue: inode_switch_wbs inode_switch_wbs_work_fn [ 1010.324832] RIP: 0010:inode_do_switch_wbs+0xaf/0x470 [ 1010.347261] Code: 00 30 0f 85 c1 03 00 00 0f 1f 44 00 00 31 d2 48 c7 c6 ff ff ff ff 48 8d 7c 24 08 e8 eb 49 1a 00 48 85 c0 74 4a bb ff ff ff ff <48> 8b 50 08 48 8d 4a ff 83 e2 01 48 0f 45 c1 48 8b 00 a8 08 0f 85 [ 1010.434307] RSP: 0018:ffff9c66691abdc8 EFLAGS: 00010002 [ 1010.457795] RAX: 0000000005b0f661 RBX: 00000000ffffffff RCX: ffff89e6a21382b0 [ 1010.489922] RDX: 0000000000000001 RSI: ffff89e350230248 RDI: ffffffffffffffff [ 1010.522085] RBP: ffff89e681d19400 R08: 0000000000000000 R09: 0000000000000228 [ 1010.554234] R10: ffffffffffffffff R11: ffffffffffffffc0 R12: ffff89e6a2138130 [ 1010.586414] R13: ffff89e316af7400 R14: ffff89e316af6e78 R15: ffff89e6a21382b0 [ 1010.619394] FS: 0000000000000000(0000) GS:ffff89ee5fb40000(0000) knlGS:0000000000000000 [ 1010.658874] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 1010.688085] CR2: 0000000005b0f669 CR3: 0000000cb2410004 CR4: 00000000001706e0 [ 1010.722129] Call Trace: [ 1010.733132] inode_switch_wbs_work_fn+0xb6/0x2a0 [ 1010.754121] process_one_work+0x1e6/0x380 [ 1010.772512] worker_thread+0x53/0x3d0 [ 1010.789221] ? process_one_work+0x380/0x380 [ 1010.807964] kthread+0x10f/0x130 [ 1010.822043] ? set_kthread_struct+0x40/0x40 [ 1010.840818] ret_from_fork+0x22/0x30 [ 1010.856851] Modules linked in: xt_CHECKSUM xt_MASQUERADE xt_conntrack ipt_REJECT nf_reject_ipv4 nft_compat nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nft_counter nf_tables nfnetlink bridge stp llc rfkill sunrpc intel_rapl_msr intel_rapl_common sb_edac x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel ipmi_ssif kvm mgag200 i2c_algo_bit iTCO_wdt irqbypass drm_kms_helper iTCO_vendor_support acpi_ipmi rapl syscopyarea sysfillrect intel_cstate ipmi_si sysimgblt ioatdma dax_pmem_compat fb_sys_fops ipmi_devintf device_dax i2c_i801 pcspkr intel_uncore hpilo nd_pmem cec dax_pmem_core dca i2c_smbus acpi_tad lpc_ich ipmi_msghandler acpi_power_meter drm fuse xfs libcrc32c sd_mod t10_pi crct10dif_pclmul crc32_pclmul crc32c_intel tg3 ghash_clmulni_intel serio_raw hpsa hpwdt scsi_transport_sas wmi dm_mirror dm_region_hash dm_log dm_mod [ 1011.200864] CR2: 0000000005b0f669 [ 1011.215700] ---[ end trace ed2105faff8384f3 ]--- [ 1011.241727] RIP: 0010:inode_do_switch_wbs+0xaf/0x470 [ 1011.264306] Code: 00 30 0f 85 c1 03 00 00 0f 1f 44 00 00 31 d2 48 c7 c6 ff ff ff ff 48 8d 7c 24 08 e8 eb 49 1a 00 48 85 c0 74 4a bb ff ff ff ff <48> 8b 50 08 48 8d 4a ff 83 e2 01 48 0f 45 c1 48 8b 00 a8 08 0f 85 [ 1011.348821] RSP: 0018:ffff9c66691abdc8 EFLAGS: 00010002 [ 1011.372734] RAX: 0000000005b0f661 RBX: 00000000ffffffff RCX: ffff89e6a21382b0 [ 1011.405826] RDX: 0000000000000001 RSI: ffff89e350230248 RDI: ffffffffffffffff [ 1011.437852] RBP: ffff89e681d19400 R08: 0000000000000000 R09: 0000000000000228 [ 1011.469926] R10: ffffffffffffffff R11: ffffffffffffffc0 R12: ffff89e6a2138130 [ 1011.502179] R13: ffff89e316af7400 R14: ffff89e316af6e78 R15: ffff89e6a21382b0 [ 1011.534233] FS: 0000000000000000(0000) GS:ffff89ee5fb40000(0000) knlGS:0000000000000000 [ 1011.571247] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 1011.597063] CR2: 0000000005b0f669 CR3: 0000000cb2410004 CR4: 00000000001706e0 [ 1011.629160] Kernel panic - not syncing: Fatal exception [ 1011.653802] Kernel Offset: 0x15200000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff) [ 1011.713723] ---[ end Kernel panic - not syncing: Fatal exception ]--- The crash happens on an attempt to iterate over attached pagecache pages and check the dirty flag: a dax inode's xarray contains pfn's instead of generic struct page pointers. This happens for DAX and not for other kinds of non-page entries in the inodes because it's a tagged iteration, and shadow/swap entries are never tagged; only DAX entries get tagged. Fix the problem by bailing out (with the false return value) of inode_prepare_sbs_switch() if a dax inode is passed. [willy@xxxxxxxxxxxxx: changelog addition] Link: https://lkml.kernel.org/r/20210719171350.3876830-1-guro@xxxxxx Fixes: c22d70a162d3 ("writeback, cgroup: release dying cgwbs by switching attached inodes") Signed-off-by: Roman Gushchin <guro@xxxxxx> Reported-by: Murphy Zhou <jencce.kernel@xxxxxxxxx> Reported-by: Darrick J. Wong <djwong@xxxxxxxxxx> Tested-by: Darrick J. Wong <djwong@xxxxxxxxxx> Tested-by: Murphy Zhou <jencce.kernel@xxxxxxxxx> Acked-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Cc: Jan Kara <jack@xxxxxxx> Cc: Dave Chinner <dchinner@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/fs-writeback.c | 3 +++ 1 file changed, 3 insertions(+) --- a/fs/fs-writeback.c~writeback-cgroup-do-not-reparent-dax-inodes +++ a/fs/fs-writeback.c @@ -521,6 +521,9 @@ static bool inode_prepare_wbs_switch(str */ smp_mb(); + if (IS_DAX(inode)) + return false; + /* while holding I_WB_SWITCH, no one else can update the association */ spin_lock(&inode->i_lock); if (!(inode->i_sb->s_flags & SB_ACTIVE) || _
