Messages in this thread | | | Date | Sat, 19 Nov 2022 07:17:37 -0800 | From | Guenter Roeck <> | Subject | Nested calls to spin_lock_irq with different locks |
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Hi,
recently I have seen various syzbot reports reporting inconsistent lock states. One example is
================================ WARNING: inconsistent lock state 5.16.0-syzkaller #0 Not tainted -------------------------------- inconsistent {IN-HARDIRQ-W} -> {HARDIRQ-ON-W} usage. syz-executor.2/18360 [HC0[0]:SC0[0]:HE0:SE1] takes: ffffffff8c712cf8 (sync_timeline_list_lock){?...}-{2:2}, at: spin_lock_irq include/linux/spinlock.h:374 [inline] ffffffff8c712cf8 (sync_timeline_list_lock){?...}-{2:2}, at: sync_info_debugfs_show+0x2d/0x200 drivers/dma-buf/sync_debug.c:147 {IN-HARDIRQ-W} state was registered at: lock_acquire kernel/locking/lockdep.c:5639 [inline] lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5604 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] _raw_spin_lock_irqsave+0x39/0x50 kernel/locking/spinlock.c:162 sync_timeline_debug_remove+0x25/0x190 drivers/dma-buf/sync_debug.c:31
================================ WARNING: inconsistent lock state 5.16.0-syzkaller #0 Not tainted -------------------------------- inconsistent {IN-HARDIRQ-W} -> {HARDIRQ-ON-W} usage. syz-executor.2/18360 [HC0[0]:SC0[0]:HE0:SE1] takes: ffffffff8c712cf8 (sync_timeline_list_lock){?...}-{2:2}, at: spin_lock_irq include/linux/spinlock.h:374 [inline] ffffffff8c712cf8 (sync_timeline_list_lock){?...}-{2:2}, at: sync_info_debugfs_show+0x2d/0x200 drivers/dma-buf/sync_debug.c:147
The log is from https://lore.kernel.org/lkml/000000000000d5b3af05edc9d445@google.com/T/.
sync_info_debugfs_show() calls spin_lock_irq(&sync_timeline_list_lock). With the lock active, it calls sync_print_obj(), which calls spin_lock_irq(&obj->lock) and spin_unlock_irq(&obj->lock).
spin_unlock_irq(), via __raw_spin_unlock_irq(), calls local_irq_enable(), presumably enabling hardware interrupts. If such a hardware interrupt calls sync_timeline_debug_remove(), the problem would be seen.
Can this happen in practice ? In other words, does that mean that nested calls to spin_lock_irq() (with different locks) are not supported ? If that is indeed the case, is there a suggested remedy ?
Thanks, Guenter
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