From a7b4c65f4f15aa657b09d13da8f45ba0b72ec0df Mon Sep 17 00:00:00 2001 From: Alex Elder Date: Fri, 9 Nov 2012 08:43:15 -0600 Subject: [PATCH] rbd: only get snap context for write requests Right now we get the snapshot context for an rbd image (under protection of the header semaphore) for every request processed. There's no need to get the snap context if we're doing a read, so avoid doing so in that case. Note that we no longer need to hold the header semaphore to check the rbd_dev's existence flag. Signed-off-by: Alex Elder Reviewed-by: Josh Durgin --- drivers/block/rbd.c | 36 ++++++++++++++++++++---------------- 1 file changed, 20 insertions(+), 16 deletions(-) diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c index 2846536d446e..0fbe9add0446 100644 --- a/drivers/block/rbd.c +++ b/drivers/block/rbd.c @@ -1331,7 +1331,7 @@ static int rbd_do_op(struct request *rq, } else { opcode = CEPH_OSD_OP_READ; flags = CEPH_OSD_FLAG_READ; - snapc = NULL; + rbd_assert(!snapc); snapid = rbd_dev->spec->snap_id; payload_len = 0; } @@ -1662,22 +1662,25 @@ static void rbd_rq_fn(struct request_queue *q) } spin_unlock_irq(q->queue_lock); - /* Stop writes to a read-only device */ - - result = -EROFS; - if (read_only && rq_data_dir(rq) == WRITE) - goto out_end_request; - - /* Grab a reference to the snapshot context */ - - down_read(&rbd_dev->header_rwsem); - if (atomic_read(&rbd_dev->exists)) { + /* Write requests need a reference to the snapshot context */ + + if (rq_data_dir(rq) == WRITE) { + result = -EROFS; + if (read_only) /* Can't write to a read-only device */ + goto out_end_request; + + /* + * Note that each osd request will take its + * own reference to the snapshot context + * supplied. The reference we take here + * just guarantees the one we provide stays + * valid. + */ + down_read(&rbd_dev->header_rwsem); snapc = ceph_get_snap_context(rbd_dev->header.snapc); + up_read(&rbd_dev->header_rwsem); rbd_assert(snapc != NULL); - } - up_read(&rbd_dev->header_rwsem); - - if (!snapc) { + } else if (!atomic_read(&rbd_dev->exists)) { rbd_assert(rbd_dev->spec->snap_id != CEPH_NOSNAP); dout("request for non-existent snapshot"); result = -ENXIO; @@ -1689,7 +1692,8 @@ static void rbd_rq_fn(struct request_queue *q) blk_rq_pos(rq) * SECTOR_SIZE, size, rq->bio); out_end_request: - ceph_put_snap_context(snapc); + if (snapc) + ceph_put_snap_context(snapc); spin_lock_irq(q->queue_lock); if (!size || result < 0) __blk_end_request_all(rq, result); -- 2.39.5