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In recent kernels, there are lockdep splats around the struct request_queue::io_lockdep_map, similar to [1], but they typically don't show up until reclaim with writeback happens. Having multiple kernel versions released with a known risc of kernel deadlock during reclaim writeback should IMHO be addressed and backported to -stable with the highest priority. In order to have these lockdep splats show up earlier, preferrably during system initialization, prime the struct request_queue::io_lockdep_map as GFP_KERNEL reclaim- tainted. This will instead lead to lockdep splats looking similar to [2], but without the need for reclaim + writeback happening. [1]: [ 189.762244] ====================================================== [ 189.762432] WARNING: possible circular locking dependency detected [ 189.762441] 6.14.0-rc6-xe+ #6 Tainted: G U [ 189.762450] ------------------------------------------------------ [ 189.762459] kswapd0/119 is trying to acquire lock: [ 189.762467] ffff888110ceb710 (&q->q_usage_counter(io)#26){++++}-{0:0}, at: __submit_bio+0x76/0x230 [ 189.762485] but task is already holding lock: [ 189.762494] ffffffff834c97c0 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat+0xbe/0xb00 [ 189.762507] which lock already depends on the new lock. [ 189.762519] the existing dependency chain (in reverse order) is: [ 189.762529] -> #2 (fs_reclaim){+.+.}-{0:0}: [ 189.762540] fs_reclaim_acquire+0xc5/0x100 [ 189.762548] kmem_cache_alloc_lru_noprof+0x4a/0x480 [ 189.762558] alloc_inode+0xaa/0xe0 [ 189.762566] iget_locked+0x157/0x330 [ 189.762573] kernfs_get_inode+0x1b/0x110 [ 189.762582] kernfs_get_tree+0x1b0/0x2e0 [ 189.762590] sysfs_get_tree+0x1f/0x60 [ 189.762597] vfs_get_tree+0x2a/0xf0 [ 189.762605] path_mount+0x4cd/0xc00 [ 189.762613] __x64_sys_mount+0x119/0x150 [ 189.762621] x64_sys_call+0x14f2/0x2310 [ 189.762630] do_syscall_64+0x91/0x180 [ 189.762637] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 189.762647] -> #1 (&root->kernfs_rwsem){++++}-{3:3}: [ 189.762659] down_write+0x3e/0xf0 [ 189.762667] kernfs_remove+0x32/0x60 [ 189.762676] sysfs_remove_dir+0x4f/0x60 [ 189.762685] __kobject_del+0x33/0xa0 [ 189.762709] kobject_del+0x13/0x30 [ 189.762716] elv_unregister_queue+0x52/0x80 [ 189.762725] elevator_switch+0x68/0x360 [ 189.762733] elv_iosched_store+0x14b/0x1b0 [ 189.762756] queue_attr_store+0x181/0x1e0 [ 189.762765] sysfs_kf_write+0x49/0x80 [ 189.762773] kernfs_fop_write_iter+0x17d/0x250 [ 189.762781] vfs_write+0x281/0x540 [ 189.762790] ksys_write+0x72/0xf0 [ 189.762798] __x64_sys_write+0x19/0x30 [ 189.762807] x64_sys_call+0x2a3/0x2310 [ 189.762815] do_syscall_64+0x91/0x180 [ 189.762823] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 189.762833] -> #0 (&q->q_usage_counter(io)#26){++++}-{0:0}: [ 189.762845] __lock_acquire+0x1525/0x2760 [ 189.762854] lock_acquire+0xca/0x310 [ 189.762861] blk_mq_submit_bio+0x8a2/0xba0 [ 189.762870] __submit_bio+0x76/0x230 [ 189.762878] submit_bio_noacct_nocheck+0x323/0x430 [ 189.762888] submit_bio_noacct+0x2cc/0x620 [ 189.762896] submit_bio+0x38/0x110 [ 189.762904] __swap_writepage+0xf5/0x380 [ 189.762912] swap_writepage+0x3c7/0x600 [ 189.762920] shmem_writepage+0x3da/0x4f0 [ 189.762929] pageout+0x13f/0x310 [ 189.762937] shrink_folio_list+0x61c/0xf60 [ 189.763261] evict_folios+0x378/0xcd0 [ 189.763584] try_to_shrink_lruvec+0x1b0/0x360 [ 189.763946] shrink_one+0x10e/0x200 [ 189.764266] shrink_node+0xc02/0x1490 [ 189.764586] balance_pgdat+0x563/0xb00 [ 189.764934] kswapd+0x1e8/0x430 [ 189.765249] kthread+0x10b/0x260 [ 189.765559] ret_from_fork+0x44/0x70 [ 189.765889] ret_from_fork_asm+0x1a/0x30 [ 189.766198] other info that might help us debug this: [ 189.767089] Chain exists of: &q->q_usage_counter(io)#26 --> &root->kernfs_rwsem --> fs_reclaim [ 189.767971] Possible unsafe locking scenario: [ 189.768555] CPU0 CPU1 [ 189.768849] ---- ---- [ 189.769136] lock(fs_reclaim); [ 189.769421] lock(&root->kernfs_rwsem); [ 189.769714] lock(fs_reclaim); [ 189.770016] rlock(&q->q_usage_counter(io)#26); [ 189.770305] *** DEADLOCK *** [ 189.771167] 1 lock held by kswapd0/119: [ 189.771453] #0: ffffffff834c97c0 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat+0xbe/0xb00 [ 189.771770] stack backtrace: [ 189.772351] CPU: 4 UID: 0 PID: 119 Comm: kswapd0 Tainted: G U 6.14.0-rc6-xe+ #6 [ 189.772353] Tainted: [U]=USER [ 189.772354] Hardware name: ASUS System Product Name/PRIME B560M-A AC, BIOS 2001 02/01/2023 [ 189.772354] Call Trace: [ 189.772355] <TASK> [ 189.772356] dump_stack_lvl+0x6e/0xa0 [ 189.772359] dump_stack+0x10/0x18 [ 189.772360] print_circular_bug.cold+0x17a/0x1b7 [ 189.772363] check_noncircular+0x13a/0x150 [ 189.772365] ? __pfx_stack_trace_consume_entry+0x10/0x10 [ 189.772368] __lock_acquire+0x1525/0x2760 [ 189.772368] ? ret_from_fork_asm+0x1a/0x30 [ 189.772371] lock_acquire+0xca/0x310 [ 189.772372] ? __submit_bio+0x76/0x230 [ 189.772375] ? lock_release+0xd5/0x2c0 [ 189.772376] blk_mq_submit_bio+0x8a2/0xba0 [ 189.772378] ? __submit_bio+0x76/0x230 [ 189.772380] __submit_bio+0x76/0x230 [ 189.772382] ? trace_hardirqs_on+0x1e/0xe0 [ 189.772384] submit_bio_noacct_nocheck+0x323/0x430 [ 189.772386] ? submit_bio_noacct_nocheck+0x323/0x430 [ 189.772387] ? __might_sleep+0x58/0xa0 [ 189.772390] submit_bio_noacct+0x2cc/0x620 [ 189.772391] ? count_memcg_events+0x68/0x90 [ 189.772393] submit_bio+0x38/0x110 [ 189.772395] __swap_writepage+0xf5/0x380 [ 189.772396] swap_writepage+0x3c7/0x600 [ 189.772397] shmem_writepage+0x3da/0x4f0 [ 189.772401] pageout+0x13f/0x310 [ 189.772406] shrink_folio_list+0x61c/0xf60 [ 189.772409] ? isolate_folios+0xe80/0x16b0 [ 189.772410] ? mark_held_locks+0x46/0x90 [ 189.772412] evict_folios+0x378/0xcd0 [ 189.772414] ? evict_folios+0x34a/0xcd0 [ 189.772415] ? lock_is_held_type+0xa3/0x130 [ 189.772417] try_to_shrink_lruvec+0x1b0/0x360 [ 189.772420] shrink_one+0x10e/0x200 [ 189.772421] shrink_node+0xc02/0x1490 [ 189.772423] ? shrink_node+0xa08/0x1490 [ 189.772424] ? shrink_node+0xbd8/0x1490 [ 189.772425] ? mem_cgroup_iter+0x366/0x480 [ 189.772427] balance_pgdat+0x563/0xb00 [ 189.772428] ? balance_pgdat+0x563/0xb00 [ 189.772430] ? trace_hardirqs_on+0x1e/0xe0 [ 189.772431] ? finish_task_switch.isra.0+0xcb/0x330 [ 189.772433] ? __switch_to_asm+0x33/0x70 [ 189.772437] kswapd+0x1e8/0x430 [ 189.772438] ? __pfx_autoremove_wake_function+0x10/0x10 [ 189.772440] ? __pfx_kswapd+0x10/0x10 [ 189.772441] kthread+0x10b/0x260 [ 189.772443] ? __pfx_kthread+0x10/0x10 [ 189.772444] ret_from_fork+0x44/0x70 [ 189.772446] ? __pfx_kthread+0x10/0x10 [ 189.772447] ret_from_fork_asm+0x1a/0x30 [ 189.772450] </TASK> [2]: [ 8.760253] ====================================================== [ 8.760254] WARNING: possible circular locking dependency detected [ 8.760255] 6.14.0-rc6-xe+ #7 Tainted: G U [ 8.760256] ------------------------------------------------------ [ 8.760257] (udev-worker)/674 is trying to acquire lock: [ 8.760259] ffff888100e39148 (&root->kernfs_rwsem){++++}-{3:3}, at: kernfs_remove+0x32/0x60 [ 8.760265] but task is already holding lock: [ 8.760266] ffff888110dc7680 (&q->q_usage_counter(io)#27){++++}-{0:0}, at: blk_mq_freeze_queue_nomemsave+0x12/0x30 [ 8.760272] which lock already depends on the new lock. [ 8.760272] the existing dependency chain (in reverse order) is: [ 8.760273] -> #2 (&q->q_usage_counter(io)#27){++++}-{0:0}: [ 8.760276] blk_alloc_queue+0x30a/0x350 [ 8.760279] blk_mq_alloc_queue+0x6b/0xe0 [ 8.760281] scsi_alloc_sdev+0x276/0x3c0 [ 8.760284] scsi_probe_and_add_lun+0x22a/0x440 [ 8.760286] __scsi_scan_target+0x109/0x230 [ 8.760288] scsi_scan_channel+0x65/0xc0 [ 8.760290] scsi_scan_host_selected+0xff/0x140 [ 8.760292] do_scsi_scan_host+0xa7/0xc0 [ 8.760293] do_scan_async+0x1c/0x160 [ 8.760295] async_run_entry_fn+0x32/0x150 [ 8.760299] process_one_work+0x224/0x5f0 [ 8.760302] worker_thread+0x1d4/0x3e0 [ 8.760304] kthread+0x10b/0x260 [ 8.760306] ret_from_fork+0x44/0x70 [ 8.760309] ret_from_fork_asm+0x1a/0x30 [ 8.760312] -> #1 (fs_reclaim){+.+.}-{0:0}: [ 8.760315] fs_reclaim_acquire+0xc5/0x100 [ 8.760317] kmem_cache_alloc_lru_noprof+0x4a/0x480 [ 8.760319] alloc_inode+0xaa/0xe0 [ 8.760322] iget_locked+0x157/0x330 [ 8.760323] kernfs_get_inode+0x1b/0x110 [ 8.760325] kernfs_get_tree+0x1b0/0x2e0 [ 8.760327] sysfs_get_tree+0x1f/0x60 [ 8.760329] vfs_get_tree+0x2a/0xf0 [ 8.760332] path_mount+0x4cd/0xc00 [ 8.760334] __x64_sys_mount+0x119/0x150 [ 8.760336] x64_sys_call+0x14f2/0x2310 [ 8.760338] do_syscall_64+0x91/0x180 [ 8.760340] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 8.760342] -> #0 (&root->kernfs_rwsem){++++}-{3:3}: [ 8.760345] __lock_acquire+0x1525/0x2760 [ 8.760347] lock_acquire+0xca/0x310 [ 8.760348] down_write+0x3e/0xf0 [ 8.760350] kernfs_remove+0x32/0x60 [ 8.760351] sysfs_remove_dir+0x4f/0x60 [ 8.760353] __kobject_del+0x33/0xa0 [ 8.760355] kobject_del+0x13/0x30 [ 8.760356] elv_unregister_queue+0x52/0x80 [ 8.760358] elevator_switch+0x68/0x360 [ 8.760360] elv_iosched_store+0x14b/0x1b0 [ 8.760362] queue_attr_store+0x181/0x1e0 [ 8.760364] sysfs_kf_write+0x49/0x80 [ 8.760366] kernfs_fop_write_iter+0x17d/0x250 [ 8.760367] vfs_write+0x281/0x540 [ 8.760370] ksys_write+0x72/0xf0 [ 8.760372] __x64_sys_write+0x19/0x30 [ 8.760374] x64_sys_call+0x2a3/0x2310 [ 8.760376] do_syscall_64+0x91/0x180 [ 8.760377] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 8.760380] other info that might help us debug this: [ 8.760380] Chain exists of: &root->kernfs_rwsem --> fs_reclaim --> &q->q_usage_counter(io)#27 [ 8.760384] Possible unsafe locking scenario: [ 8.760384] CPU0 CPU1 [ 8.760385] ---- ---- [ 8.760385] lock(&q->q_usage_counter(io)#27); [ 8.760387] lock(fs_reclaim); [ 8.760388] lock(&q->q_usage_counter(io)#27); [ 8.760390] lock(&root->kernfs_rwsem); [ 8.760391] *** DEADLOCK *** [ 8.760391] 6 locks held by (udev-worker)/674: [ 8.760392] #0: ffff8881209ac420 (sb_writers#4){.+.+}-{0:0}, at: ksys_write+0x72/0xf0 [ 8.760398] #1: ffff88810c80f488 (&of->mutex#2){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x136/0x250 [ 8.760402] #2: ffff888125d1d330 (kn->active#101){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x13f/0x250 [ 8.760406] #3: ffff888110dc7bb0 (&q->sysfs_lock){+.+.}-{3:3}, at: queue_attr_store+0x148/0x1e0 [ 8.760411] #4: ffff888110dc7680 (&q->q_usage_counter(io)#27){++++}-{0:0}, at: blk_mq_freeze_queue_nomemsave+0x12/0x30 [ 8.760416] #5: ffff888110dc76b8 (&q->q_usage_counter(queue)#27){++++}-{0:0}, at: blk_mq_freeze_queue_nomemsave+0x12/0x30 [ 8.760421] stack backtrace: [ 8.760422] CPU: 7 UID: 0 PID: 674 Comm: (udev-worker) Tainted: G U 6.14.0-rc6-xe+ #7 [ 8.760424] Tainted: [U]=USER [ 8.760425] Hardware name: ASUS System Product Name/PRIME B560M-A AC, BIOS 2001 02/01/2023 [ 8.760426] Call Trace: [ 8.760427] <TASK> [ 8.760428] dump_stack_lvl+0x6e/0xa0 [ 8.760431] dump_stack+0x10/0x18 [ 8.760433] print_circular_bug.cold+0x17a/0x1b7 [ 8.760437] check_noncircular+0x13a/0x150 [ 8.760441] ? save_trace+0x54/0x360 [ 8.760445] __lock_acquire+0x1525/0x2760 [ 8.760446] ? irqentry_exit+0x3a/0xb0 [ 8.760448] ? sysvec_apic_timer_interrupt+0x57/0xc0 [ 8.760452] lock_acquire+0xca/0x310 [ 8.760453] ? kernfs_remove+0x32/0x60 [ 8.760457] down_write+0x3e/0xf0 [ 8.760459] ? kernfs_remove+0x32/0x60 [ 8.760460] kernfs_remove+0x32/0x60 [ 8.760462] sysfs_remove_dir+0x4f/0x60 [ 8.760464] __kobject_del+0x33/0xa0 [ 8.760466] kobject_del+0x13/0x30 [ 8.760467] elv_unregister_queue+0x52/0x80 [ 8.760470] elevator_switch+0x68/0x360 [ 8.760472] elv_iosched_store+0x14b/0x1b0 [ 8.760475] queue_attr_store+0x181/0x1e0 [ 8.760479] ? lock_acquire+0xca/0x310 [ 8.760480] ? kernfs_fop_write_iter+0x13f/0x250 [ 8.760482] ? lock_is_held_type+0xa3/0x130 [ 8.760485] sysfs_kf_write+0x49/0x80 [ 8.760487] kernfs_fop_write_iter+0x17d/0x250 [ 8.760489] vfs_write+0x281/0x540 [ 8.760494] ksys_write+0x72/0xf0 [ 8.760497] __x64_sys_write+0x19/0x30 [ 8.760499] x64_sys_call+0x2a3/0x2310 [ 8.760502] do_syscall_64+0x91/0x180 [ 8.760504] ? trace_hardirqs_off+0x5d/0xe0 [ 8.760506] ? handle_softirqs+0x479/0x4d0 [ 8.760508] ? hrtimer_interrupt+0x13f/0x280 [ 8.760511] ? irqentry_exit_to_user_mode+0x8b/0x260 [ 8.760513] ? clear_bhb_loop+0x15/0x70 [ 8.760515] ? clear_bhb_loop+0x15/0x70 [ 8.760516] ? clear_bhb_loop+0x15/0x70 [ 8.760518] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 8.760520] RIP: 0033:0x7aa3bf2f5504 [ 8.760522] Code: c7 00 16 00 00 00 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 80 3d c5 8b 10 00 00 74 13 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 54 c3 0f 1f 00 55 48 89 e5 48 83 ec 20 48 89 [ 8.760523] RSP: 002b:00007ffc1e3697d8 EFLAGS: 00000202 ORIG_RAX: 0000000000000001 [ 8.760526] RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007aa3bf2f5504 [ 8.760527] RDX: 0000000000000003 RSI: 00007ffc1e369ae0 RDI: 000000000000001c [ 8.760528] RBP: 00007ffc1e369800 R08: 00007aa3bf3f51c8 R09: 00007ffc1e3698b0 [ 8.760528] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000003 [ 8.760529] R13: 00007ffc1e369ae0 R14: 0000613ccf21f2f0 R15: 00007aa3bf3f4e80 [ 8.760533] </TASK> v2: - Update a code comment to increase readability (Ming Lei). Cc: Jens Axboe <axboe@kernel.dk> Cc: linux-block@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: Ming Lei <ming.lei@redhat.com> Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com> Reviewed-by: Ming Lei <ming.lei@redhat.com> Link: https://lore.kernel.org/r/20250318095548.5187-1-thomas.hellstrom@linux.intel.com Signed-off-by: Jens Axboe <axboe@kernel.dk>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.