This is a note to let you know that I've just added the patch titled
block: Don't access request after it might be freed
to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
block-don-t-access-request-after-it-might-be-freed.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 893d290f1d7496db97c9471bc352ad4a11dc8a25 Mon Sep 17 00:00:00 2001
From: Roland Dreier <roland@xxxxxxxxxxxxxxx>
Date: Thu, 22 Nov 2012 02:00:11 -0800
Subject: block: Don't access request after it might be freed
From: Roland Dreier <roland@xxxxxxxxxxxxxxx>
commit 893d290f1d7496db97c9471bc352ad4a11dc8a25 upstream.
After we've done __elv_add_request() and __blk_run_queue() in
blk_execute_rq_nowait(), the request might finish and be freed
immediately. Therefore checking if the type is REQ_TYPE_PM_RESUME
isn't safe afterwards, because if it isn't, rq might be gone.
Instead, check beforehand and stash the result in a temporary.
This fixes crashes in blk_execute_rq_nowait() I get occasionally when
running with lots of memory debugging options enabled -- I think this
race is usually harmless because the window for rq to be reallocated
is so small.
Signed-off-by: Roland Dreier <roland@xxxxxxxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
[xr: Backported to 3.4: adjust context]
Signed-off-by: Rui Xiang <rui.xiang@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
block/blk-exec.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
--- a/block/blk-exec.c
+++ b/block/blk-exec.c
@@ -49,8 +49,18 @@ void blk_execute_rq_nowait(struct reques
rq_end_io_fn *done)
{
int where = at_head ? ELEVATOR_INSERT_FRONT : ELEVATOR_INSERT_BACK;
+ bool is_pm_resume;
WARN_ON(irqs_disabled());
+
+ rq->rq_disk = bd_disk;
+ rq->end_io = done;
+ /*
+ * need to check this before __blk_run_queue(), because rq can
+ * be freed before that returns.
+ */
+ is_pm_resume = rq->cmd_type == REQ_TYPE_PM_RESUME;
+
spin_lock_irq(q->queue_lock);
if (unlikely(blk_queue_dead(q))) {
@@ -66,7 +76,7 @@ void blk_execute_rq_nowait(struct reques
__elv_add_request(q, rq, where);
__blk_run_queue(q);
/* the queue is stopped so it won't be run */
- if (rq->cmd_type == REQ_TYPE_PM_RESUME)
+ if (is_pm_resume)
q->request_fn(q);
spin_unlock_irq(q->queue_lock);
}
Patches currently in stable-queue which might be from roland@xxxxxxxxxxxxxxx are
queue-3.4/block-don-t-access-request-after-it-might-be-freed.patch
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