Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755223Ab0BSRCx (ORCPT ); Fri, 19 Feb 2010 12:02:53 -0500 Received: from kroah.org ([198.145.64.141]:57874 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755129Ab0BSRBV (ORCPT ); Fri, 19 Feb 2010 12:01:21 -0500 X-Mailbox-Line: From gregkh@kvm.kroah.org Fri Feb 19 08:32:57 2010 Message-Id: <20100219163257.186977438@kvm.kroah.org> User-Agent: quilt/0.48-4.4 Date: Fri, 19 Feb 2010 08:30:26 -0800 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Kiyoshi Ueda , Junichi Nomura , Alasdair G Kergon Subject: [93/93] dm mpath: fix stall when requeueing io In-Reply-To: <20100219165717.GA15002@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3296 Lines: 107 2.6.32-stable review patch. If anyone has any objections, please let us know. ------------------ From: Kiyoshi Ueda commit 9eef87da2a8ea4920e0d913ff977cac064b68ee0 upstream. This patch fixes the problem that system may stall if target's ->map_rq returns DM_MAPIO_REQUEUE in map_request(). E.g. stall happens on 1 CPU box when a dm-mpath device with queue_if_no_path bounces between all-paths-down and paths-up on I/O load. When target's ->map_rq returns DM_MAPIO_REQUEUE, map_request() requeues the request and returns to dm_request_fn(). Then, dm_request_fn() doesn't exit the I/O dispatching loop and continues processing the requeued request again. This map and requeue loop can be done with interrupt disabled, so 1 CPU system can be stalled if this situation happens. For example, commands below can stall my 1 CPU box within 1 minute or so: # dmsetup table mp mp: 0 2097152 multipath 1 queue_if_no_path 0 1 1 service-time 0 1 2 8:144 1 1 # while true; do dd if=/dev/mapper/mp of=/dev/null bs=1M count=100; done & # while true; do \ > dmsetup message mp 0 "fail_path 8:144" \ > dmsetup suspend --noflush mp \ > dmsetup resume mp \ > dmsetup message mp 0 "reinstate_path 8:144" \ > done To fix the problem above, this patch changes dm_request_fn() to exit the I/O dispatching loop once if a request is requeued in map_request(). Signed-off-by: Kiyoshi Ueda Signed-off-by: Jun'ichi Nomura Signed-off-by: Alasdair G Kergon Signed-off-by: Greg Kroah-Hartman --- drivers/md/dm.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-) --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -1487,11 +1487,15 @@ static int dm_prep_fn(struct request_que return BLKPREP_OK; } -static void map_request(struct dm_target *ti, struct request *rq, - struct mapped_device *md) +/* + * Returns: + * 0 : the request has been processed (not requeued) + * !0 : the request has been requeued + */ +static int map_request(struct dm_target *ti, struct request *clone, + struct mapped_device *md) { - int r; - struct request *clone = rq->special; + int r, requeued = 0; struct dm_rq_target_io *tio = clone->end_io_data; /* @@ -1516,6 +1520,7 @@ static void map_request(struct dm_target case DM_MAPIO_REQUEUE: /* The target wants to requeue the I/O */ dm_requeue_unmapped_request(clone); + requeued = 1; break; default: if (r > 0) { @@ -1527,6 +1532,8 @@ static void map_request(struct dm_target dm_kill_unmapped_request(clone, r); break; } + + return requeued; } /* @@ -1568,12 +1575,16 @@ static void dm_request_fn(struct request blk_start_request(rq); spin_unlock(q->queue_lock); - map_request(ti, rq, md); + if (map_request(ti, rq, md)) + goto requeued; spin_lock_irq(q->queue_lock); } goto out; +requeued: + spin_lock_irq(q->queue_lock); + plug_and_out: if (!elv_queue_empty(q)) /* Some requests still remain, retry later */ -- 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/