[PATCH] Fix lock inversion aio_kick_handler()
lockdep found a AB BC CA lock inversion in retry-based AIO:
1) The task struct's alloc_lock (A) is acquired in process context with
interrupts enabled. An interrupt might arrive and call wake_up() which
grabs the wait queue's q->lock (B).
2) When performing retry-based AIO the AIO core registers
aio_wake_function() as the wake funtion for iocb->ki_wait. It is called
with the wait queue's q->lock (B) held and then tries to add the iocb to
the run list after acquiring the ctx_lock (C).
3) aio_kick_handler() holds the ctx_lock (C) while acquiring the
alloc_lock (A) via lock_task() and unuse_mm(). Lockdep emits a warning
saying that we're trying to connect the irq-safe q->lock to the
irq-unsafe alloc_lock via ctx_lock.
This fixes the inversion by calling unuse_mm() in the AIO kick handing path
after we've released the ctx_lock. As Ben LaHaise pointed out __put_ioctx
could set ctx->mm to NULL, so we must only access ctx->mm while we have the
lock.
Signed-off-by: Zach Brown <zach.brown@oracle.com>
Signed-off-by: Suparna Bhattacharya <suparna@in.ibm.com>
Acked-by: Benjamin LaHaise <bcrl@kvack.org>
Cc: "Chen, Kenneth W" <kenneth.w.chen@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
1 file changed