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authorKiyoshi Ueda2010-02-16 18:43:01 +0000
committerAlasdair G Kergon2010-02-16 18:43:01 +0000
commit9eef87da2a8ea4920e0d913ff977cac064b68ee0 (patch)
tree811eb358ce2fa66517b0cf59501522c17dfbe6bc
parent558569aa9d83e016295bac77d900342908d7fd85 (diff)
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 <k-ueda@ct.jp.nec.com> Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com> Cc: stable@kernel.org Signed-off-by: Alasdair G Kergon <agk@redhat.com>
-rw-r--r--drivers/md/dm.c21
1 files changed, 17 insertions, 4 deletions
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 3167480b532c..aa4e2aa86d49 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1595,10 +1595,15 @@ static int dm_prep_fn(struct request_queue *q, struct request *rq)
return BLKPREP_OK;
}
-static void map_request(struct dm_target *ti, struct request *clone,
- 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;
+ int r, requeued = 0;
struct dm_rq_target_io *tio = clone->end_io_data;
/*
@@ -1625,6 +1630,7 @@ static void map_request(struct dm_target *ti, struct request *clone,
case DM_MAPIO_REQUEUE:
/* The target wants to requeue the I/O */
dm_requeue_unmapped_request(clone);
+ requeued = 1;
break;
default:
if (r > 0) {
@@ -1636,6 +1642,8 @@ static void map_request(struct dm_target *ti, struct request *clone,
dm_kill_unmapped_request(clone, r);
break;
}
+
+ return requeued;
}
/*
@@ -1677,12 +1685,17 @@ static void dm_request_fn(struct request_queue *q)
atomic_inc(&md->pending[rq_data_dir(clone)]);
spin_unlock(q->queue_lock);
- map_request(ti, clone, md);
+ if (map_request(ti, clone, 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 */