rbd: access snapshot context and mapping size safely
These fields may both change while the image is mapped if a snapshot is created or deleted or the image is resized. They are guarded by rbd_dev->header_rwsem, so hold that while reading them, and store a local copy to refer to outside of the critical section. The local copy will stay consistent since the snapshot context is reference counted, and the mapping size is just a u64. This prevents torn loads from giving us inconsistent values. Move reading header.snapc into the caller of rbd_img_request_create() so that we only need to take the semaphore once. The read-only caller, rbd_parent_request_create() can just pass NULL for snapc, since the snapshot context is only relevant for writes. Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
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@ -2057,7 +2057,8 @@ static bool rbd_dev_parent_get(struct rbd_device *rbd_dev)
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static struct rbd_img_request *rbd_img_request_create(
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struct rbd_device *rbd_dev,
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u64 offset, u64 length,
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bool write_request)
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bool write_request,
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struct ceph_snap_context *snapc)
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{
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struct rbd_img_request *img_request;
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@ -2065,12 +2066,6 @@ static struct rbd_img_request *rbd_img_request_create(
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if (!img_request)
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return NULL;
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if (write_request) {
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down_read(&rbd_dev->header_rwsem);
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ceph_get_snap_context(rbd_dev->header.snapc);
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up_read(&rbd_dev->header_rwsem);
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}
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img_request->rq = NULL;
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img_request->rbd_dev = rbd_dev;
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img_request->offset = offset;
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@ -2078,7 +2073,7 @@ static struct rbd_img_request *rbd_img_request_create(
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img_request->flags = 0;
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if (write_request) {
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img_request_write_set(img_request);
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img_request->snapc = rbd_dev->header.snapc;
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img_request->snapc = snapc;
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} else {
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img_request->snap_id = rbd_dev->spec->snap_id;
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}
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@ -2134,8 +2129,8 @@ static struct rbd_img_request *rbd_parent_request_create(
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rbd_assert(obj_request->img_request);
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rbd_dev = obj_request->img_request->rbd_dev;
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parent_request = rbd_img_request_create(rbd_dev->parent,
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img_offset, length, false);
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parent_request = rbd_img_request_create(rbd_dev->parent, img_offset,
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length, false, NULL);
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if (!parent_request)
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return NULL;
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@ -3183,9 +3178,11 @@ out:
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static void rbd_handle_request(struct rbd_device *rbd_dev, struct request *rq)
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{
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struct rbd_img_request *img_request;
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struct ceph_snap_context *snapc = NULL;
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u64 offset = (u64)blk_rq_pos(rq) << SECTOR_SHIFT;
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u64 length = blk_rq_bytes(rq);
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bool wr = rq_data_dir(rq) == WRITE;
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u64 mapping_size;
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int result;
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/* Ignore/skip any zero-length requests */
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@ -3226,14 +3223,23 @@ static void rbd_handle_request(struct rbd_device *rbd_dev, struct request *rq)
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goto err_rq; /* Shouldn't happen */
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}
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if (offset + length > rbd_dev->mapping.size) {
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down_read(&rbd_dev->header_rwsem);
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mapping_size = rbd_dev->mapping.size;
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if (wr) {
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snapc = rbd_dev->header.snapc;
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ceph_get_snap_context(snapc);
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}
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up_read(&rbd_dev->header_rwsem);
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if (offset + length > mapping_size) {
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rbd_warn(rbd_dev, "beyond EOD (%llu~%llu > %llu)", offset,
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length, rbd_dev->mapping.size);
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length, mapping_size);
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result = -EIO;
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goto err_rq;
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}
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img_request = rbd_img_request_create(rbd_dev, offset, length, wr);
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img_request = rbd_img_request_create(rbd_dev, offset, length, wr,
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snapc);
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if (!img_request) {
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result = -ENOMEM;
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goto err_rq;
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@ -3256,6 +3262,8 @@ err_rq:
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if (result)
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rbd_warn(rbd_dev, "%s %llx at %llx result %d",
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wr ? "write" : "read", length, offset, result);
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if (snapc)
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ceph_put_snap_context(snapc);
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blk_end_request_all(rq, result);
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}
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