From: Kiyoshi Ueda Date: Tue, 16 Feb 2010 18:43:01 +0000 (+0000) Subject: dm mpath: fix stall when requeueing io X-Git-Tag: v2.6.33~39^2~1 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9eef87da2a8ea4920e0d913ff977cac064b68ee0;p=pandora-kernel.git dm mpath: fix stall when requeueing io 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 Cc: stable@kernel.org Signed-off-by: Alasdair G Kergon --- Reading git-diff-tree failed