[BLOCK] limit request_fn recursion
Don't recurse back into the driver even if the unplug threshold is met,
when the driver asks for a requeue. This is both silly from a logical
point of view (requeues typically happen due to driver/hardware
shortage), and also dangerous since we could hit an endless request_fn
-> requeue -> unplug -> request_fn loop and crash on stack overrun.
Also limit blk_run_queue() to one level of recursion, similar to how
blk_start_queue() works.
This patch fixed a real problem with SLES10 and lpfc, and it could hit
any SCSI lld that returns non-zero from it's ->queuecommand() handler.
Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/block/elevator.c b/block/elevator.c
index 2982579..8768a36 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -333,6 +333,7 @@
{
struct list_head *pos;
unsigned ordseq;
+ int unplug_it = 1;
blk_add_trace_rq(q, rq, BLK_TA_INSERT);
@@ -399,6 +400,11 @@
}
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;
default:
@@ -407,7 +413,7 @@
BUG();
}
- if (blk_queue_plugged(q)) {
+ if (unplug_it && blk_queue_plugged(q)) {
int nrq = q->rq.count[READ] + q->rq.count[WRITE]
- q->in_flight;