Commit:     1ebb1101c556b1915ff041655e629a072e64dcda
Parent:     43cdff92ad47e0ca024c8a07d29f9bb6119e759c
Author:     Zach Brown <[EMAIL PROTECTED]>
AuthorDate: Fri Dec 29 16:47:02 2006 -0800
Committer:  Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Sat Dec 30 10:55:54 2006 -0800

    [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
    Signed-off-by: Zach Brown <[EMAIL PROTECTED]>
    Signed-off-by: Suparna Bhattacharya <[EMAIL PROTECTED]>
    Acked-by: Benjamin LaHaise <[EMAIL PROTECTED]>
    Cc: "Chen, Kenneth W" <[EMAIL PROTECTED]>
    Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
    Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
 fs/aio.c |    7 +++----
 1 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 5f577a6..ee20fc4 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,;
        mm_segment_t oldfs = get_fs();
+       struct mm_struct *mm;
        int requeue;
        requeue =__aio_run_iocbs(ctx);
-       unuse_mm(ctx->mm);
+       mm = ctx->mm;
+       unuse_mm(mm);
         * we're in a worker thread already, don't use queue_delayed_work,
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