Right now we get and release the header semaphore every time we process a request for an rbd image. We do this because for write requests we need to supply the snapshot context, and we can't safely get a reference to it without holding that semaphore.
There's no need to get the snap context if we're doing a read, so avoid doing so in that case. The rbd_device->exists field can be updated asynchronously, changing from set to clear if a mapped snapshot disappears from the base image's snapshot context. Although I don't think synchronizing access to this carefully is that critical, it is converted here to be an atomic variable so a request is aware the flag is clear as soon as that is known. Signed-off-by: Alex Elder <[email protected]> --- drivers/block/rbd.c | 25 ++++++++++++------------- 1 file changed, 12 insertions(+), 13 deletions(-) diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c index b86f5e5..bac4304 100644 --- a/drivers/block/rbd.c +++ b/drivers/block/rbd.c @@ -229,7 +229,7 @@ struct rbd_device { spinlock_t lock; /* queue lock */ struct rbd_image_header header; - bool exists; + atomic_t exists; struct rbd_spec *spec; char *header_name; @@ -753,7 +753,7 @@ static int rbd_dev_set_mapping(struct rbd_device *rbd_dev) goto done; rbd_dev->mapping.read_only = true; } - rbd_dev->exists = true; + atomic_set(&rbd_dev->exists, 1); done: return ret; } @@ -1333,8 +1333,7 @@ static int rbd_do_op(struct request *rq, } else { opcode = CEPH_OSD_OP_READ; flags = CEPH_OSD_FLAG_READ; - ceph_put_snap_context(snapc); - snapc = NULL; + rbd_assert(!snapc); snapid = rbd_dev->spec->snap_id; payload_len = 0; } @@ -1652,6 +1651,7 @@ static void rbd_rq_fn(struct request_queue *q) while ((rq = blk_fetch_request(q))) { struct ceph_snap_context *snapc = NULL; + bool write_request = rq_data_dir(rq) == WRITE; int result; dout("fetched request\n"); @@ -1667,19 +1667,17 @@ static void rbd_rq_fn(struct request_queue *q) /* Stop writes to a read-only device */ result = -EROFS; - if (read_only && rq_data_dir(rq) == WRITE) + if (read_only && write_request) goto out_end_request; - /* Grab a reference to the snapshot context */ + /* Grab a reference to the snapshot context if needed */ - down_read(&rbd_dev->header_rwsem); - if (rbd_dev->exists) { + if (write_request) { + down_read(&rbd_dev->header_rwsem); snapc = ceph_get_snap_context(rbd_dev->header.snapc); rbd_assert(snapc != NULL); - } - up_read(&rbd_dev->header_rwsem); - - if (!snapc) { + up_read(&rbd_dev->header_rwsem); + } else if (!atomic_read(&rbd_dev->exists)) { rbd_assert(rbd_dev->spec->snap_id != CEPH_NOSNAP); dout("request for non-existent snapshot"); result = -ENXIO; @@ -2295,6 +2293,7 @@ struct rbd_device *rbd_dev_create(struct rbd_client *rbdc, return NULL; spin_lock_init(&rbd_dev->lock); + atomic_set(&rbd_dev->exists, 0); INIT_LIST_HEAD(&rbd_dev->node); INIT_LIST_HEAD(&rbd_dev->snaps); init_rwsem(&rbd_dev->header_rwsem); @@ -2919,7 +2918,7 @@ static int rbd_dev_snaps_update(struct rbd_device *rbd_dev) /* Existing snapshot not in the new snap context */ if (rbd_dev->spec->snap_id == snap->id) - rbd_dev->exists = false; + atomic_set(&rbd_dev->exists, 0); rbd_remove_snap_dev(snap); dout("%ssnap id %llu has been removed\n", rbd_dev->spec->snap_id == snap->id ? -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
