blk-iolatency: fix child_lat lock irq state#915
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iolatency_clear_scaling() updates child_lat.lock with hardirqs enabled. The bio completion path can take the same lock from hardirq context. This triggers lockdep after io.latency is configured and I/O completes. Full lockdep report: WARNING: inconsistent lock state 7.1.0-rc2-g6a04b2279273 #1 Not tainted -------------------------------- inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage. swapper/0/0 [HC1[1]:SC0[0]:HE0:SE1] takes: ffff88810c682d10 (&iolat->child_lat.lock){?.+.}-{3:3}, at: blkcg_iolatency_done_bio+0x6e7/0xb90 {HARDIRQ-ON-W} state was registered at: lock_acquire+0xd4/0x290 _raw_spin_lock+0x3a/0x70 iolatency_set_limit+0x49b/0x590 cgroup_file_write+0x1c5/0x4b0 kernfs_fop_write_iter+0x1d7/0x280 vfs_write+0x580/0x630 ksys_write+0xec/0x190 do_syscall_64+0x156/0x490 entry_SYSCALL_64_after_hwframe+0x77/0x7f irq event stamp: 328476 hardirqs last enabled at (328475): [<ffffffffa4dd93b1>] do_idle+0x261/0x400 hardirqs last disabled at (328476): [<ffffffffa68347f3>] common_interrupt+0x13/0x90 softirqs last enabled at (328398): [<ffffffffa4d508ac>] __irq_exit_rcu+0x8c/0x150 softirqs last disabled at (328387): [<ffffffffa4d508ac>] __irq_exit_rcu+0x8c/0x150 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(&iolat->child_lat.lock); <Interrupt> lock(&iolat->child_lat.lock); *** DEADLOCK *** 1 lock held by swapper/0/0: #0: ffff888103365450 (&virtscsi_vq->vq_lock){-.-.}-{3:3}, at: virtscsi_vq_done+0x9f/0x130 stack backtrace: CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 7.1.0-rc2-g6a04b2279273 #1 PREEMPT 1c49bdb9e32f352d2b66a5ca23d36d656c610458 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-5.fc42 04/01/2014 Call Trace: <IRQ> dump_stack_lvl+0x54/0x70 print_usage_bug+0x26d/0x280 mark_lock_irq+0x3ef/0x400 ? save_trace+0x3d/0x2f0 ? __pfx_stack_trace_consume_entry+0x10/0x10 mark_lock+0x117/0x190 __lock_acquire+0x570/0x2850 ? stack_trace_save+0xa1/0xe0 ? __pfx_stack_trace_save+0x10/0x10 ? filter_irq_stacks+0x27/0x80 ? stack_depot_save_flags+0x32/0x7f0 lock_acquire+0xd4/0x290 ? blkcg_iolatency_done_bio+0x6e7/0xb90 ? kvm_sched_clock_read+0x11/0x20 ? local_clock_noinstr+0xc/0xc0 ? local_clock+0x15/0x30 ? lock_release+0x111/0x470 ? blkcg_iolatency_done_bio+0x6e7/0xb90 _raw_spin_lock_irqsave+0x4c/0x90 ? blkcg_iolatency_done_bio+0x6e7/0xb90 blkcg_iolatency_done_bio+0x6e7/0xb90 ? __pfx_blkcg_iolatency_done_bio+0x10/0x10 __rq_qos_done_bio+0x51/0x60 bio_endio+0x135/0x320 blk_update_request+0x1e6/0x570 scsi_end_request+0x4b/0x410 scsi_io_completion+0x83/0x170 ? __pfx_virtscsi_complete_cmd+0x10/0x10 virtscsi_vq_done+0xd7/0x130 ? lock_acquire+0xd4/0x290 ? __pfx_virtscsi_vq_done+0x10/0x10 ? local_clock_noinstr+0xc/0xc0 ? local_clock+0x15/0x30 vring_interrupt+0x13b/0x150 ? __pfx_vring_interrupt+0x10/0x10 __handle_irq_event_percpu+0x145/0x4b0 handle_irq_event+0x54/0xb0 handle_edge_irq+0x111/0x320 __common_interrupt+0x97/0xf0 common_interrupt+0x7e/0x90 </IRQ> <TASK> asm_common_interrupt+0x26/0x40 RIP: 0010:pv_native_safe_halt+0x13/0x20 Code: d3 a5 01 00 cc 66 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d 2f 39 21 00 f3 0f 1e fa fb f4 <c3> cc cc cc cc cc 0f 1f 80 00 00 00 00 90 90 90 90 90 90 90 90 90 RSP: 0018:ffffffffa7607e00 EFLAGS: 00000246 RAX: 000000000005031b RBX: ffffffffa4dd93b1 RCX: ffffffffa683884b RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffffffa4dd93b1 RBP: ffffffffa7607ed0 R08: ffff888117bf408b R09: 1ffff11022f7e811 R10: dffffc0000000000 R11: ffffed1022f7e812 R12: 0000000000000000 R13: 0000000000000000 R14: 0000000000000000 R15: ffffffffa7f6cff0 ? do_idle+0x261/0x400 ? ct_kernel_exit+0xcb/0x110 ? do_idle+0x261/0x400 default_idle+0x9/0x20 default_idle_call+0x73/0xb0 do_idle+0x261/0x400 ? __pfx_do_idle+0x10/0x10 ? local_clock_noinstr+0x30/0xc0 ? local_clock+0x15/0x30 cpu_startup_entry+0x36/0x40 rest_init+0x207/0x210 start_kernel+0x321/0x370 x86_64_start_reservations+0x24/0x30 x86_64_start_kernel+0x13a/0x140 common_startup_64+0x13e/0x147 </TASK> Fix it by using spin_lock_irqsave() in iolatency_clear_scaling(). Use irqsave rather than spin_lock_irq() because the same helper is also called from pd_offline_fn paths where hardirqs can already be disabled by blkcg teardown/deactivation locks. spin_unlock_irq() would wrongly enable hardirqs in those paths. Fixes: d706751 ("block: introduce blk-iolatency io controller") Signed-off-by: Yu Kuai <yukuai@fygo.io>
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Pull request for series with
subject: blk-iolatency: fix child_lat lock irq state
version: 1
url: https://patchwork.kernel.org/project/linux-block/list/?series=1103827