On Thu, 2012-12-13 at 11:58 -0200, Herton Ronaldo Krzesinski wrote: > 3.5.7.2 -stable review patch. If anyone has any objections, please let me > know. > > ------------------ > > From: Roland Dreier <rol...@purestorage.com> > > 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 <rol...@purestorage.com> > Signed-off-by: Jens Axboe <ax...@kernel.dk> > [ herton: adjust context ] > Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesin...@canonical.com>
This is missing from 3.{0,4} but I did apply it to 3.2, again with the
need to adjust context.
Perhaps the intermediate fixes to blk_execute_rq_nowait() that resulted
in the changed context should also be applied to stable updates. The
fixes in question are:
8ba61435d73f block: add missing blk_queue_dead() checks
- applied in 3.3; missing from 3.{0,2}.y
e81ca6fe85b7 [SCSI] block: Fix blk_execute_rq_nowait() dead queue handling
- applied in 3.6; missing from 3.{0,2,4,5}.y
893d290f1d74 block: Don't access request after it might be freed
- applied in 3.7, then to 3.{2,6}.y; missing from 3.{0,4}.y
Jens?
Ben.
> ---
> block/blk-exec.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/block/blk-exec.c b/block/blk-exec.c
> index fb2cbd5..9925fbe 100644
> --- a/block/blk-exec.c
> +++ b/block/blk-exec.c
> @@ -49,8 +49,16 @@ void blk_execute_rq_nowait(struct request_queue *q, struct
> gendisk *bd_disk,
> rq_end_io_fn *done)
> {
> int where = at_head ? ELEVATOR_INSERT_FRONT : ELEVATOR_INSERT_BACK;
> + bool is_pm_resume;
>
> WARN_ON(irqs_disabled());
> +
> + /*
> + * 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 +74,7 @@ void blk_execute_rq_nowait(struct request_queue *q, struct
> gendisk *bd_disk,
> __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);
> }
--
Ben Hutchings
Theory and practice are closer in theory than in practice.
- John Levine, moderator of comp.compilers
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