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Lockdep reported a warning in Linux version 6.6:
[ 414.344659] ================================
[ 414.345155] WARNING: inconsistent lock state
[ 414.345658] 6.6.0-07439-gba2303cacfda #6 Not tainted
[ 414.346221] --------------------------------
[ 414.346712] inconsistent {IN-SOFTIRQ-W} -> {SOFTIRQ-ON-W} usage.
[ 414.347545] kworker/u10:3/1152 [HC0[0]:SC0[0]:HE0:SE1] takes:
[ 414.349245] ffff88810edd1098 (&sbq->ws[i].wait){+.?.}-{2:2}, at: blk_mq_dispatch_rq_list+0x131c/0x1ee0
[ 414.351204] {IN-SOFTIRQ-W} state was registered at:
[ 414.351751] lock_acquire+0x18d/0x460
[ 414.352218] _raw_spin_lock_irqsave+0x39/0x60
[ 414.352769] __wake_up_common_lock+0x22/0x60
[ 414.353289] sbitmap_queue_wake_up+0x375/0x4f0
[ 414.353829] sbitmap_queue_clear+0xdd/0x270
[ 414.354338] blk_mq_put_tag+0xdf/0x170
[ 414.354807] __blk_mq_free_request+0x381/0x4d0
[ 414.355335] blk_mq_free_request+0x28b/0x3e0
[ 414.355847] __blk_mq_end_request+0x242/0xc30
[ 414.356367] scsi_end_request+0x2c1/0x830
[ 414.345155] WARNING: inconsistent lock state
[ 414.345658] 6.6.0-07439-gba2303cacfda #6 Not tainted
[ 414.346221] --------------------------------
[ 414.346712] inconsistent {IN-SOFTIRQ-W} -> {SOFTIRQ-ON-W} usage.
[ 414.347545] kworker/u10:3/1152 [HC0[0]:SC0[0]:HE0:SE1] takes:
[ 414.349245] ffff88810edd1098 (&sbq->ws[i].wait){+.?.}-{2:2}, at: blk_mq_dispatch_rq_list+0x131c/0x1ee0
[ 414.351204] {IN-SOFTIRQ-W} state was registered at:
[ 414.351751] lock_acquire+0x18d/0x460
[ 414.352218] _raw_spin_lock_irqsave+0x39/0x60
[ 414.352769] __wake_up_common_lock+0x22/0x60
[ 414.353289] sbitmap_queue_wake_up+0x375/0x4f0
[ 414.353829] sbitmap_queue_clear+0xdd/0x270
[ 414.354338] blk_mq_put_tag+0xdf/0x170
[ 414.354807] __blk_mq_free_request+0x381/0x4d0
[ 414.355335] blk_mq_free_request+0x28b/0x3e0
[ 414.355847] __blk_mq_end_request+0x242/0xc30
[ 414.356367] scsi_end_request+0x2c1/0x830
[ 414.356863] scsi_io_completion+0x177/0x1610
[ 414.357379] scsi_complete+0x12f/0x260
[ 414.357856] blk_complete_reqs+0xba/0xf0
[ 414.358338] __do_softirq+0x1b0/0x7a2
[ 414.358796] irq_exit_rcu+0x14b/0x1a0
[ 414.359262] sysvec_call_function_single+0xaf/0xc0
[ 414.359828] asm_sysvec_call_function_single+0x1a/0x20
[ 414.360426] default_idle+0x1e/0x30
[ 414.360873] default_idle_call+0x9b/0x1f0
[ 414.361390] do_idle+0x2d2/0x3e0
[ 414.361819] cpu_startup_entry+0x55/0x60
[ 414.362314] start_secondary+0x235/0x2b0
[ 414.362809] secondary_startup_64_no_verify+0x18f/0x19b
[ 414.363413] irq event stamp: 428794
[ 414.363825] hardirqs last enabled at (428793): [<ffffffff816bfd1c>] ktime_get+0x1dc/0x200
[ 414.364694] hardirqs last disabled at (428794): [<ffffffff85470177>] _raw_spin_lock_irq+0x47/0x50
[ 414.365629] softirqs last enabled at (428444): [<ffffffff85474780>] __do_softirq+0x540/0x7a2
[ 414.366522] softirqs last disabled at (428419): [<ffffffff813f65ab>] irq_exit_rcu+0x14b/0x1a0
[ 414.367425]
other info that might help us debug this:
[ 414.368194] Possible unsafe locking scenario:
[ 414.368900] CPU0
[ 414.369225] ----
[ 414.369548] lock(&sbq->ws[i].wait);
[ 414.370000] <Interrupt>
[ 414.370342] lock(&sbq->ws[i].wait);
[ 414.370802]
*** DEADLOCK ***
[ 414.371569] 5 locks held by kworker/u10:3/1152:
[ 414.372088] #0: ffff88810130e938 ((wq_completion)writeback){+.+.}-{0:0}, at: process_scheduled_works+0x357/0x13f0
[ 414.373180] #1: ffff88810201fdb8 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_scheduled_works+0x3a3/0x13f0
[ 414.374384] #2: ffffffff86ffbdc0 (rcu_read_lock){....}-{1:2}, at: blk_mq_run_hw_queue+0x637/0xa00
[ 414.375342] #3: ffff88810edd1098 (&sbq->ws[i].wait){+.?.}-{2:2}, at: blk_mq_dispatch_rq_list+0x131c/0x1ee0
[ 414.376377] #4: ffff888106205a08 (&hctx->dispatch_wait_lock){+.-.}-{2:2}, at: blk_mq_dispatch_rq_list+0x1337/0x1ee0
[ 414.378607]
stack backtrace:
[ 414.379177] CPU: 0 PID: 1152 Comm: kworker/u10:3 Not tainted 6.6.0-07439-gba2303cacfda #6
[ 414.380032] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[ 414.381177] Workqueue: writeback wb_workfn (flush-253:0)
[ 414.381805] Call Trace:
[ 414.382136] <TASK>
[ 414.382429] dump_stack_lvl+0x91/0xf0
[ 414.382884] mark_lock_irq+0xb3b/0x1260
[ 414.383367] ? __pfx_mark_lock_irq+0x10/0x10
[ 414.383889] ? stack_trace_save+0x8e/0xc0
[ 414.384373] ? __pfx_stack_trace_save+0x10/0x10
[ 414.384903] ? graph_lock+0xcf/0x410
[ 414.385350] ? save_trace+0x3d/0xc70
[ 414.385808] mark_lock.part.20+0x56d/0xa90
[ 414.386317] mark_held_locks+0xb0/0x110
[ 414.386791] ? __pfx_do_raw_spin_lock+0x10/0x10
[ 414.387320] lockdep_hardirqs_on_prepare+0x297/0x3f0
[ 414.387901] ? _raw_spin_unlock_irq+0x28/0x50
[ 414.388422] trace_hardirqs_on+0x58/0x100
[ 414.388917] _raw_spin_unlock_irq+0x28/0x50
[ 414.389422] __blk_mq_tag_busy+0x1d6/0x2a0
[ 414.389920] __blk_mq_get_driver_tag+0x761/0x9f0
[ 414.390899] blk_mq_dispatch_rq_list+0x1780/0x1ee0
[ 414.391473] ? __pfx_blk_mq_dispatch_rq_list+0x10/0x10
[ 414.392070] ? sbitmap_get+0x2b8/0x450
[ 414.392533] ? __blk_mq_get_driver_tag+0x210/0x9f0
[ 414.393095] __blk_mq_sched_dispatch_requests+0xd99/0x1690
[ 414.393730] ? elv_attempt_insert_merge+0x1b1/0x420
[ 414.394302] ? __pfx___blk_mq_sched_dispatch_requests+0x10/0x10
[ 414.394970] ? lock_acquire+0x18d/0x460
[ 414.395456] ? blk_mq_run_hw_queue+0x637/0xa00
[ 414.395986] ? __pfx_lock_acquire+0x10/0x10
[ 414.396499] blk_mq_sched_dispatch_requests+0x109/0x190
[ 414.397100] blk_mq_run_hw_queue+0x66e/0xa00
[ 414.397616] blk_mq_flush_plug_list.part.17+0x614/0x2030
[ 414.398244] ? __pfx_blk_mq_flush_plug_list.part.17+0x10/0x10
[ 414.398897] ? writeback_sb_inodes+0x241/0xcc0
[ 414.399429] blk_mq_flush_plug_list+0x65/0x80
[ 414.399957] __blk_flush_plug+0x2f1/0x530
[ 414.400458] ? __pfx___blk_flush_plug+0x10/0x10
[ 414.400999] blk_finish_plug+0x59/0xa0
[ 414.401467] wb_writeback+0x7cc/0x920
[ 414.401935] ? __pfx_wb_writeback+0x10/0x10
[ 414.402442] ? mark_held_locks+0xb0/0x110
[ 414.402931] ? __pfx_do_raw_spin_lock+0x10/0x10
[ 414.403462] ? lockdep_hardirqs_on_prepare+0x297/0x3f0
[ 414.404062] wb_workfn+0x2b3/0xcf0
[ 414.404500] ? __pfx_wb_workfn+0x10/0x10
[ 414.404989] process_scheduled_works+0x432/0x13f0
[ 414.405546] ? __pfx_process_scheduled_works+0x10/0x10
[ 414.406139] ? do_raw_spin_lock+0x101/0x2a0
[ 414.406641] ? assign_work+0x19b/0x240
[ 414.407106] ? lock_is_held_type+0x9d/0x110
[ 414.407604] worker_thread+0x6f2/0x1160
[ 414.408075] ? __kthread_parkme+0x62/0x210
[ 414.408572] ? lockdep_hardirqs_on_prepare+0x297/0x3f0
[ 414.409168] ? __kthread_parkme+0x13c/0x210
[ 414.409678] ? __pfx_worker_thread+0x10/0x10
[ 414.410191] kthread+0x33c/0x440
[ 414.410602] ? __pfx_kthread+0x10/0x10
[ 414.411068] ret_from_fork+0x4d/0x80
[ 414.411526] ? __pfx_kthread+0x10/0x10
[ 414.411993] ret_from_fork_asm+0x1b/0x30
[ 414.412489] </TASK>
When interrupt is turned on while a lock holding by spin_lock_irq it
throws a warning because of potential deadlock.
blk_mq_prep_dispatch_rq
blk_mq_get_driver_tag
__blk_mq_get_driver_tag
__blk_mq_alloc_driver_tag
blk_mq_tag_busy -> tag is already busy
// failed to get driver tag
blk_mq_mark_tag_wait
spin_lock_irq(&wq->lock) -> lock A (&sbq->ws[i].wait)
__add_wait_queue(wq, wait) -> wait queue active
blk_mq_get_driver_tag
__blk_mq_tag_busy
-> 1) tag must be idle, which means there can't be inflight IO
spin_lock_irq(&tags->lock) -> lock B (hctx->tags)
spin_unlock_irq(&tags->lock) -> unlock B, turn on interrupt accidentally
-> 2) context must be preempt by IO interrupt to trigger deadlock.
As shown above, the deadlock is not possible in theory, but the warning
still need to be fixed.
Fix it by using spin_lock_irqsave to get lockB instead of spin_lock_irq.
Fixes:
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Linux kernel
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In order to build the documentation, use ``make htmldocs`` or
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