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rbd: use reference counting for the snap context 

This prevents a race between requests with a given snap context and
header updates that free it. The osd client was already expecting the
snap context to be reference counted, since it get()s it in
ceph_osdc_build_request and put()s it when the request completes.

Also remove the second down_read()/up_read() on header_rwsem in
rbd_do_request, which wasn't actually preventing this race or
protecting any other data.

Signed-off-by: Josh Durgin <josh.durgin@dreamhost.com>
Reviewed-by: Alex Elder <elder@inktank.com>
This commit is contained in:
Josh Durgin 2011-12-05 14:03:05 -08:00 committed by Sage Weil
parent 93a24e084d
commit d1d2564654
1 changed files with 18 additions and 18 deletions
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36
drivers/block/rbd.c
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@ -626,7 +626,7 @@ static void rbd_header_free(struct rbd_image_header *header)
kfree(header->object_prefix);
kfree(header->snap_sizes);
kfree(header->snap_names);
kfree(header->snapc);
ceph_put_snap_context(header->snapc);
}
/*
@ -902,13 +902,10 @@ static int rbd_do_request(struct request *rq,
dout("rbd_do_request object_name=%s ofs=%lld len=%lld\n",
object_name, len, ofs);
down_read(&rbd_dev->header_rwsem);
osdc = &rbd_dev->rbd_client->client->osdc;
req = ceph_osdc_alloc_request(osdc, flags, snapc, ops,
false, GFP_NOIO, pages, bio);
if (!req) {
up_read(&rbd_dev->header_rwsem);
ret = -ENOMEM;
goto done_pages;
}
@ -942,7 +939,6 @@ static int rbd_do_request(struct request *rq,
snapc,
&mtime,
req->r_oid, req->r_oid_len);
up_read(&rbd_dev->header_rwsem);
if (linger_req) {
ceph_osdc_set_request_linger(osdc, req);
@ -1448,6 +1444,7 @@ static void rbd_rq_fn(struct request_queue *q)
u64 ofs;
int num_segs, cur_seg = 0;
struct rbd_req_coll *coll;
struct ceph_snap_context *snapc;
/* peek at request from block layer */
if (!rq)
@ -1474,21 +1471,20 @@ static void rbd_rq_fn(struct request_queue *q)
spin_unlock_irq(q->queue_lock);
if (rbd_dev->snap_id != CEPH_NOSNAP) {
bool snap_exists;
down_read(&rbd_dev->header_rwsem);
down_read(&rbd_dev->header_rwsem);
snap_exists = rbd_dev->snap_exists;
if (rbd_dev->snap_id != CEPH_NOSNAP && !rbd_dev->snap_exists) {
up_read(&rbd_dev->header_rwsem);
if (!snap_exists) {
dout("request for non-existent snapshot");
spin_lock_irq(q->queue_lock);
__blk_end_request_all(rq, -ENXIO);
continue;
}
dout("request for non-existent snapshot");
spin_lock_irq(q->queue_lock);
__blk_end_request_all(rq, -ENXIO);
continue;
}
snapc = ceph_get_snap_context(rbd_dev->header.snapc);
up_read(&rbd_dev->header_rwsem);
dout("%s 0x%x bytes at 0x%llx\n",
do_write ? "write" : "read",
size, blk_rq_pos(rq) * SECTOR_SIZE);
@ -1498,6 +1494,7 @@ static void rbd_rq_fn(struct request_queue *q)
if (!coll) {
spin_lock_irq(q->queue_lock);
__blk_end_request_all(rq, -ENOMEM);
ceph_put_snap_context(snapc);
continue;
}
@ -1521,7 +1518,7 @@ static void rbd_rq_fn(struct request_queue *q)
/* init OSD command: write or read */
if (do_write)
rbd_req_write(rq, rbd_dev,
rbd_dev->header.snapc,
snapc,
ofs,
op_size, bio,
coll, cur_seg);
@ -1544,6 +1541,8 @@ next_seg:
if (bp)
bio_pair_release(bp);
spin_lock_irq(q->queue_lock);
ceph_put_snap_context(snapc);
}
}
@ -1744,7 +1743,8 @@ static int __rbd_refresh_header(struct rbd_device *rbd_dev)
/* rbd_dev->header.object_prefix shouldn't change */
kfree(rbd_dev->header.snap_sizes);
kfree(rbd_dev->header.snap_names);
kfree(rbd_dev->header.snapc);
/* osd requests may still refer to snapc */
ceph_put_snap_context(rbd_dev->header.snapc);
rbd_dev->header.image_size = h.image_size;
rbd_dev->header.total_snaps = h.total_snaps;