On Mon, Jan 15 2007, Linas Vepstas wrote:
>
> Hi Chris, Jens,
> Can you look at this, and push upstream if this looks reasonable
> to you? It fixes a bug I've been tripping over.
>
> --linas
>
>
> A flag was recently added to the elevator code to avoid
> performing an unplug when reuests are being re-queued.
> The goal of this flag was to avoid a deep recursion that
> can occur when re-queueing requests after a SCSI device/host
> reset. See http://lkml.org/lkml/2006/5/17/254
>
> However, that fix added the flag near the bottom of a case
> statement, where an earlier break (in an if statement) could
> transport one out of the case, without setting the flag.
> This patch sets the flag earlier in the case statement.
>
> I re-discovered the deep recursion recently during testing;
> I was told that it was a known problem, and the fix to it was
> in the kernel I was testing. Indeed it was ... but it didn't
> fix the bug. With the patch below, I no longer see the bug.
>
> Signed-off by: Linas Vepstas <[email protected]>
> Cc: Jens Axboe <[email protected]>
> Cc: Chris Wright <[email protected]>
>
> ----
> block/elevator.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> Index: linux-2.6.20-rc4/block/elevator.c
> ===================================================================
> --- linux-2.6.20-rc4.orig/block/elevator.c 2007-01-15 14:16:03.000000000 -0600
> +++ linux-2.6.20-rc4/block/elevator.c 2007-01-15 14:20:04.000000000 -0600
> @@ -590,6 +590,12 @@ void elv_insert(request_queue_t *q, stru
> */
> rq->cmd_flags |= REQ_SOFTBARRIER;
>
> + /*
> + * Most requeues happen because of a busy condition,
> + * don't force unplug of the queue for that case.
> + */
> + unplug_it = 0;
> +
> if (q->ordseq == 0) {
> list_add(&rq->queuelist, &q->queue_head);
> break;
> @@ -604,11 +610,6 @@ void elv_insert(request_queue_t *q, stru
> }
>
> list_add_tail(&rq->queuelist, pos);
> - /*
> - * most requeues happen because of a busy condition, don't
> - * force unplug of the queue for that case.
> - */
> - unplug_it = 0;
> break;
Ah, yes it definitely should be moved up, thanks for that!
Acked-by: Jens Axboe <[email protected]>
I'll get this merged for 2.6.21.
--
Jens Axboe
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
