From: Zach Brown Date: Sat, 30 Dec 2006 00:47:02 +0000 (-0800) Subject: [PATCH] Fix lock inversion aio_kick_handler() X-Git-Tag: v2.6.20-rc3~52 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1ebb1101c556b1915ff041655e629a072e64dcda;p=linux-2.6 [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 Signed-off-by: Suparna Bhattacharya Acked-by: Benjamin LaHaise Cc: "Chen, Kenneth W" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/fs/aio.c b/fs/aio.c index 5f577a63bd..ee20fc4240 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -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 *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,