diff options
| author | Kiyoshi Ueda <k-ueda@ct.jp.nec.com> | 2010-02-16 18:43:01 +0000 |
|---|---|---|
| committer | Alasdair G Kergon <agk@redhat.com> | 2010-02-16 18:43:01 +0000 |
| commit | 9eef87da2a8ea4920e0d913ff977cac064b68ee0 (patch) | |
| tree | 811eb358ce2fa66517b0cf59501522c17dfbe6bc | |
| parent | 558569aa9d83e016295bac77d900342908d7fd85 (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.c | 21 |
1 files changed, 17 insertions, 4 deletions
diff --git a/drivers/md/dm.c b/drivers/md/dm.c index 3167480b532..aa4e2aa86d4 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 */ |