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Commit 4e752f0a authored by Josh Durgin's avatar Josh Durgin Committed by Ilya Dryomov
Browse files

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: default avatarJosh Durgin <josh.durgin@inktank.com>
parent 7dd440c9

drivers/block/rbd.c

+21 −13
Original line number Diff line number Diff line
@@ -2057,7 +2057,8 @@ static bool rbd_dev_parent_get(struct rbd_device *rbd_dev) 
static struct rbd_img_request *rbd_img_request_create(

					struct rbd_device *rbd_dev,

					u64 offset, u64 length,

					bool write_request)

					bool write_request,

					struct ceph_snap_context *snapc)

{

	struct rbd_img_request *img_request;
@@ -2065,12 +2066,6 @@ static struct rbd_img_request *rbd_img_request_create( 
	if (!img_request)

		return NULL;



	if (write_request) {

		down_read(&rbd_dev->header_rwsem);

		ceph_get_snap_context(rbd_dev->header.snapc);

		up_read(&rbd_dev->header_rwsem);

	}



	img_request->rq = NULL;

	img_request->rbd_dev = rbd_dev;

	img_request->offset = offset;
@@ -2078,7 +2073,7 @@ static struct rbd_img_request *rbd_img_request_create( 
	img_request->flags = 0;

	if (write_request) {

		img_request_write_set(img_request);

		img_request->snapc = rbd_dev->header.snapc;

		img_request->snapc = snapc;

	} else {

		img_request->snap_id = rbd_dev->spec->snap_id;

	}
@@ -2134,8 +2129,8 @@ static struct rbd_img_request *rbd_parent_request_create( 
	rbd_assert(obj_request->img_request);

	rbd_dev = obj_request->img_request->rbd_dev;



	parent_request = rbd_img_request_create(rbd_dev->parent,

						img_offset, length, false);

	parent_request = rbd_img_request_create(rbd_dev->parent, img_offset,

						length, false, NULL);

	if (!parent_request)

		return NULL;
@@ -3183,9 +3178,11 @@ static int rbd_obj_method_sync(struct rbd_device *rbd_dev, 
static void rbd_handle_request(struct rbd_device *rbd_dev, struct request *rq)

{

	struct rbd_img_request *img_request;

	struct ceph_snap_context *snapc = NULL;

	u64 offset = (u64)blk_rq_pos(rq) << SECTOR_SHIFT;

	u64 length = blk_rq_bytes(rq);

	bool wr = rq_data_dir(rq) == WRITE;

	u64 mapping_size;

	int result;



	/* Ignore/skip any zero-length requests */
@@ -3226,14 +3223,23 @@ static void rbd_handle_request(struct rbd_device *rbd_dev, struct request *rq) 
		goto err_rq;	/* Shouldn't happen */

	}



	if (offset + length > rbd_dev->mapping.size) {

	down_read(&rbd_dev->header_rwsem);

	mapping_size = rbd_dev->mapping.size;

	if (wr) {

		snapc = rbd_dev->header.snapc;

		ceph_get_snap_context(snapc);

	}

	up_read(&rbd_dev->header_rwsem);



	if (offset + length > mapping_size) {

		rbd_warn(rbd_dev, "beyond EOD (%llu~%llu > %llu)", offset,

			 length, rbd_dev->mapping.size);

			 length, mapping_size);

		result = -EIO;

		goto err_rq;

	}



	img_request = rbd_img_request_create(rbd_dev, offset, length, wr);

	img_request = rbd_img_request_create(rbd_dev, offset, length, wr,

					     snapc);

	if (!img_request) {

		result = -ENOMEM;

		goto err_rq;
@@ -3256,6 +3262,8 @@ static void rbd_handle_request(struct rbd_device *rbd_dev, struct request *rq) 
	if (result)

		rbd_warn(rbd_dev, "%s %llx at %llx result %d",

			 wr ? "write" : "read", length, offset, result);

	if (snapc)

		ceph_put_snap_context(snapc);

	blk_end_request_all(rq, result);

}