From: Zach Brown 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 Signed-off-by: Suparna Bhattacharya =================================================================== --- --- linux-2.6.20-rc1-root/fs/aio.c | 7 +++---- 1 files changed, 3 insertions(+), 4 deletions(-) diff -puN fs/aio.c~aio-fix-unusemm-ctx-lockinversion fs/aio.c --- linux-2.6.20-rc1/fs/aio.c~aio-fix-unusemm-ctx-lockinversion 2006-12-20 12:40:12.000000000 +0530 +++ linux-2.6.20-rc1-root/fs/aio.c 2006-12-20 12:40:12.000000000 +0530 @@ -599,9 +599,6 @@ static void use_mm(struct mm_struct *mm) * by the calling kernel thread * (Note: this routine is intended to be called only * from a kernel thread context) - * - * Comments: Called with ctx->ctx_lock held. This nests - * task_lock instead ctx_lock. */ static void unuse_mm(struct mm_struct *mm) { @@ -850,14 +847,16 @@ static void aio_kick_handler(struct work { struct kioctx *ctx = container_of(work, struct kioctx, wq.work); mm_segment_t oldfs = get_fs(); + struct mm_struct *mm; int requeue; set_fs(USER_DS); use_mm(ctx->mm); spin_lock_irq(&ctx->ctx_lock); requeue =__aio_run_iocbs(ctx); - unuse_mm(ctx->mm); + mm = ctx->mm; spin_unlock_irq(&ctx->ctx_lock); + unuse_mm(mm); set_fs(oldfs); /* * we're in a worker thread already, don't use queue_delayed_work, _