Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=1ebb1101c556b1915ff041655e629a072e64dcda
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
lock.
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, 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,
-
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