Messages in this thread Patch in this message | | | Date | Wed, 17 May 2006 00:00:13 -0700 | From | Chris Wright <> | Subject | [PATCH 13/22] [PATCH] [BLOCK] limit request_fn recursion |
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-stable review patch. If anyone has any objections, please let us know. ------------------
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> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> Signed-off-by: Chris Wright <chrisw@sous-sol.org>
--- block/elevator.c | 8 +++++++- block/ll_rw_blk.c | 17 +++++++++++++++-- 2 files changed, 22 insertions(+), 3 deletions(-)
--- linux-2.6.16.16.orig/block/elevator.c +++ linux-2.6.16.16/block/elevator.c @@ -314,6 +314,7 @@ void elv_insert(request_queue_t *q, stru { struct list_head *pos; unsigned ordseq; + int unplug_it = 1; rq->q = q; @@ -378,6 +379,11 @@ 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; default: @@ -386,7 +392,7 @@ void elv_insert(request_queue_t *q, stru 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; --- linux-2.6.16.16.orig/block/ll_rw_blk.c +++ linux-2.6.16.16/block/ll_rw_blk.c @@ -1719,8 +1719,21 @@ void blk_run_queue(struct request_queue spin_lock_irqsave(q->queue_lock, flags); blk_remove_plug(q); - if (!elv_queue_empty(q)) - q->request_fn(q); + + /* + * Only recurse once to avoid overrunning the stack, let the unplug + * handling reinvoke the handler shortly if we already got there. + */ + if (!elv_queue_empty(q)) { + if (!test_and_set_bit(QUEUE_FLAG_REENTER, &q->queue_flags)) { + q->request_fn(q); + clear_bit(QUEUE_FLAG_REENTER, &q->queue_flags); + } else { + blk_plug_device(q); + kblockd_schedule_work(&q->unplug_work); + } + } + spin_unlock_irqrestore(q->queue_lock, flags); } EXPORT_SYMBOL(blk_run_queue); -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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