[PATCH for 5.4] rbd: get snapshot context after exclusive lock is ensured to be held

[PATCH for 5.4] rbd: get snapshot context after exclusive lock is ensured to be held

[Ilya Dryomov]

Move capturing the snapshot context into the image request state
machine, after exclusive lock is ensured to be held for the duration of
dealing with the image request.  This is needed to ensure correctness
of fast-diff states (OBJECT_EXISTS vs OBJECT_EXISTS_CLEAN) and object
deltas computed based off of them.  Otherwise the object map that is
forked for the snapshot isn't guaranteed to accurately reflect the
contents of the snapshot when the snapshot is taken under I/O.  This
breaks differential backup and snapshot-based mirroring use cases with
fast-diff enabled: since some object deltas may be incomplete, the
destination image may get corrupted.

Cc: stable@vger.kernel.org
Link: https://tracker.ceph.com/issues/61472
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Dongsheng Yang <dongsheng.yang@easystack.cn>
[idryomov@gmail.com: backport to 5.4: no rbd_img_capture_header(),
 img_request not embedded in blk-mq pdu]
---
 drivers/block/rbd.c | 41 ++++++++++++++++++++++++-----------------
 1 file changed, 24 insertions(+), 17 deletions(-)

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 22b282409a16..9d21f90f93f0 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -1495,6 +1495,8 @@ static bool rbd_obj_is_tail(struct rbd_obj_request *obj_req)
  */
 static void rbd_obj_set_copyup_enabled(struct rbd_obj_request *obj_req)
 {
+	rbd_assert(obj_req->img_request->snapc);
+
 	if (obj_req->img_request->op_type == OBJ_OP_DISCARD) {
 		dout("%s %p objno %llu discard\n", __func__, obj_req,
 		     obj_req->ex.oe_objno);
@@ -1613,6 +1615,7 @@ __rbd_obj_add_osd_request(struct rbd_obj_request *obj_req,
 static struct ceph_osd_request *
 rbd_obj_add_osd_request(struct rbd_obj_request *obj_req, int num_ops)
 {
+	rbd_assert(obj_req->img_request->snapc);
 	return __rbd_obj_add_osd_request(obj_req, obj_req->img_request->snapc,
 					 num_ops);
 }
@@ -1741,11 +1744,14 @@ static bool rbd_dev_parent_get(struct rbd_device *rbd_dev)
  * Caller is responsible for filling in the list of object requests
  * that comprises the image request, and the Linux request pointer
  * (if there is one).
+ *
+ * Only snap_id is captured here, for reads.  For writes, snapshot
+ * context is captured in rbd_img_object_requests() after exclusive
+ * lock is ensured to be held.
  */
 static struct rbd_img_request *rbd_img_request_create(
 					struct rbd_device *rbd_dev,
-					enum obj_operation_type op_type,
-					struct ceph_snap_context *snapc)
+					enum obj_operation_type op_type)
 {
 	struct rbd_img_request *img_request;
 
@@ -1757,8 +1763,6 @@ static struct rbd_img_request *rbd_img_request_create(
 	img_request->op_type = op_type;
 	if (!rbd_img_is_write(img_request))
 		img_request->snap_id = rbd_dev->spec->snap_id;
-	else
-		img_request->snapc = snapc;
 
 	if (rbd_dev_parent_get(rbd_dev))
 		img_request_layered_set(img_request);
@@ -2944,7 +2948,7 @@ static int rbd_obj_read_from_parent(struct rbd_obj_request *obj_req)
 	int ret;
 
 	child_img_req = rbd_img_request_create(img_req->rbd_dev->parent,
-					       OBJ_OP_READ, NULL);
+					       OBJ_OP_READ);
 	if (!child_img_req)
 		return -ENOMEM;
 
@@ -3635,9 +3639,19 @@ static int rbd_img_exclusive_lock(struct rbd_img_request *img_req)
 
 static void rbd_img_object_requests(struct rbd_img_request *img_req)
 {
+	struct rbd_device *rbd_dev = img_req->rbd_dev;
 	struct rbd_obj_request *obj_req;
 
 	rbd_assert(!img_req->pending.result && !img_req->pending.num_pending);
+	rbd_assert(!need_exclusive_lock(img_req) ||
+		   __rbd_is_lock_owner(rbd_dev));
+
+	if (rbd_img_is_write(img_req)) {
+		rbd_assert(!img_req->snapc);
+		down_read(&rbd_dev->header_rwsem);
+		img_req->snapc = ceph_get_snap_context(rbd_dev->header.snapc);
+		up_read(&rbd_dev->header_rwsem);
+	}
 
 	for_each_obj_request(img_req, obj_req) {
 		int result = 0;
@@ -3655,7 +3669,6 @@ static void rbd_img_object_requests(struct rbd_img_request *img_req)
 
 static bool rbd_img_advance(struct rbd_img_request *img_req, int *result)
 {
-	struct rbd_device *rbd_dev = img_req->rbd_dev;
 	int ret;
 
 again:
@@ -3676,9 +3689,6 @@ static bool rbd_img_advance(struct rbd_img_request *img_req, int *result)
 		if (*result)
 			return true;
 
-		rbd_assert(!need_exclusive_lock(img_req) ||
-			   __rbd_is_lock_owner(rbd_dev));
-
 		rbd_img_object_requests(img_req);
 		if (!img_req->pending.num_pending) {
 			*result = img_req->pending.result;
@@ -4140,6 +4150,10 @@ static int rbd_post_acquire_action(struct rbd_device *rbd_dev)
 {
 	int ret;
 
+	ret = rbd_dev_refresh(rbd_dev);
+	if (ret)
+		return ret;
+
 	if (rbd_dev->header.features & RBD_FEATURE_OBJECT_MAP) {
 		ret = rbd_object_map_open(rbd_dev);
 		if (ret)
@@ -4798,7 +4812,6 @@ static void rbd_queue_workfn(struct work_struct *work)
 	struct request *rq = blk_mq_rq_from_pdu(work);
 	struct rbd_device *rbd_dev = rq->q->queuedata;
 	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);
 	enum obj_operation_type op_type;
@@ -4863,10 +4876,6 @@ static void rbd_queue_workfn(struct work_struct *work)
 
 	down_read(&rbd_dev->header_rwsem);
 	mapping_size = rbd_dev->mapping.size;
-	if (op_type != OBJ_OP_READ) {
-		snapc = rbd_dev->header.snapc;
-		ceph_get_snap_context(snapc);
-	}
 	up_read(&rbd_dev->header_rwsem);
 
 	if (offset + length > mapping_size) {
@@ -4876,13 +4885,12 @@ static void rbd_queue_workfn(struct work_struct *work)
 		goto err_rq;
 	}
 
-	img_request = rbd_img_request_create(rbd_dev, op_type, snapc);
+	img_request = rbd_img_request_create(rbd_dev, op_type);
 	if (!img_request) {
 		result = -ENOMEM;
 		goto err_rq;
 	}
 	img_request->rq = rq;
-	snapc = NULL; /* img_request consumes a ref */
 
 	dout("%s rbd_dev %p img_req %p %s %llu~%llu\n", __func__, rbd_dev,
 	     img_request, obj_op_name(op_type), offset, length);
@@ -4904,7 +4912,6 @@ static void rbd_queue_workfn(struct work_struct *work)
 	if (result)
 		rbd_warn(rbd_dev, "%s %llx at %llx result %d",
 			 obj_op_name(op_type), length, offset, result);
-	ceph_put_snap_context(snapc);
 err:
 	blk_mq_end_request(rq, errno_to_blk_status(result));
 }
-- 
2.40.1

Re: [PATCH for 5.4] rbd: get snapshot context after exclusive lock is ensured to be held

[Greg KH]

On Sun, Jun 11, 2023 at 08:41:27PM +0200, Ilya Dryomov wrote:
> Move capturing the snapshot context into the image request state
> machine, after exclusive lock is ensured to be held for the duration of
> dealing with the image request.  This is needed to ensure correctness
> of fast-diff states (OBJECT_EXISTS vs OBJECT_EXISTS_CLEAN) and object
> deltas computed based off of them.  Otherwise the object map that is
> forked for the snapshot isn't guaranteed to accurately reflect the
> contents of the snapshot when the snapshot is taken under I/O.  This
> breaks differential backup and snapshot-based mirroring use cases with
> fast-diff enabled: since some object deltas may be incomplete, the
> destination image may get corrupted.
> 
> Cc: stable@vger.kernel.org
> Link: https://tracker.ceph.com/issues/61472
> Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
> Reviewed-by: Dongsheng Yang <dongsheng.yang@easystack.cn>
> [idryomov@gmail.com: backport to 5.4: no rbd_img_capture_header(),
>  img_request not embedded in blk-mq pdu]
> ---
>  drivers/block/rbd.c | 41 ++++++++++++++++++++++++-----------------
>  1 file changed, 24 insertions(+), 17 deletions(-)

What is the commit id in Linus's tree of this change?

thanks,

greg k-h

Re: [PATCH for 5.4] rbd: get snapshot context after exclusive lock is ensured to be held

[Ilya Dryomov]

On Mon, Jun 12, 2023 at 11:25 AM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Sun, Jun 11, 2023 at 08:41:27PM +0200, Ilya Dryomov wrote:
> > Move capturing the snapshot context into the image request state
> > machine, after exclusive lock is ensured to be held for the duration of
> > dealing with the image request.  This is needed to ensure correctness
> > of fast-diff states (OBJECT_EXISTS vs OBJECT_EXISTS_CLEAN) and object
> > deltas computed based off of them.  Otherwise the object map that is
> > forked for the snapshot isn't guaranteed to accurately reflect the
> > contents of the snapshot when the snapshot is taken under I/O.  This
> > breaks differential backup and snapshot-based mirroring use cases with
> > fast-diff enabled: since some object deltas may be incomplete, the
> > destination image may get corrupted.
> >
> > Cc: stable@vger.kernel.org
> > Link: https://tracker.ceph.com/issues/61472
> > Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
> > Reviewed-by: Dongsheng Yang <dongsheng.yang@easystack.cn>
> > [idryomov@gmail.com: backport to 5.4: no rbd_img_capture_header(),
> >  img_request not embedded in blk-mq pdu]
> > ---
> >  drivers/block/rbd.c | 41 ++++++++++++++++++++++++-----------------
> >  1 file changed, 24 insertions(+), 17 deletions(-)
>
> What is the commit id in Linus's tree of this change?

Hi Greg,

It's 870611e4877eff1e8413c3fb92a585e45d5291f6.

Thanks,

                Ilya

Re: [PATCH for 5.4] rbd: get snapshot context after exclusive lock is ensured to be held

[Greg KH]

On Mon, Jun 12, 2023 at 11:32:32AM +0200, Ilya Dryomov wrote:
> On Mon, Jun 12, 2023 at 11:25 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> >
> > On Sun, Jun 11, 2023 at 08:41:27PM +0200, Ilya Dryomov wrote:
> > > Move capturing the snapshot context into the image request state
> > > machine, after exclusive lock is ensured to be held for the duration of
> > > dealing with the image request.  This is needed to ensure correctness
> > > of fast-diff states (OBJECT_EXISTS vs OBJECT_EXISTS_CLEAN) and object
> > > deltas computed based off of them.  Otherwise the object map that is
> > > forked for the snapshot isn't guaranteed to accurately reflect the
> > > contents of the snapshot when the snapshot is taken under I/O.  This
> > > breaks differential backup and snapshot-based mirroring use cases with
> > > fast-diff enabled: since some object deltas may be incomplete, the
> > > destination image may get corrupted.
> > >
> > > Cc: stable@vger.kernel.org
> > > Link: https://tracker.ceph.com/issues/61472
> > > Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
> > > Reviewed-by: Dongsheng Yang <dongsheng.yang@easystack.cn>
> > > [idryomov@gmail.com: backport to 5.4: no rbd_img_capture_header(),
> > >  img_request not embedded in blk-mq pdu]
> > > ---
> > >  drivers/block/rbd.c | 41 ++++++++++++++++++++++++-----------------
> > >  1 file changed, 24 insertions(+), 17 deletions(-)
> >
> > What is the commit id in Linus's tree of this change?
> 
> Hi Greg,
> 
> It's 870611e4877eff1e8413c3fb92a585e45d5291f6.

Great, now queued up, thanks.

greg k-h