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 <linas@xxxxxxxxxxxxxx> > Cc: Jens Axboe <axboe@xxxxxxx> > Cc: Chris Wright <chrisw@xxxxxxxxxxxx> > > ---- > 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 <jens.axboe@xxxxxxxxxx> I'll get this merged for 2.6.21. -- Jens Axboe - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
