Re: [PATCH] ceph: force updating the msg pointer in non-split case

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On 5/17/23 19:29, Ilya Dryomov wrote:
On Wed, May 17, 2023 at 1:04 PM Xiubo Li <xiubli@xxxxxxxxxx> wrote:

On 5/17/23 18:31, Ilya Dryomov wrote:
On Wed, May 17, 2023 at 7:24 AM <xiubli@xxxxxxxxxx> wrote:
From: Xiubo Li <xiubli@xxxxxxxxxx>

When the MClientSnap reqeust's op is not CEPH_SNAP_OP_SPLIT the
request may still contain a list of 'split_realms', and we need
to skip it anyway. Or it will be parsed as a corrupt snaptrace.

Cc: stable@xxxxxxxxxxxxxxx
Cc: Frank Schilder <frans@xxxxxx>
Reported-by: Frank Schilder <frans@xxxxxx>
URL: https://tracker.ceph.com/issues/61200
Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx>
---
   fs/ceph/snap.c | 3 +++
   1 file changed, 3 insertions(+)

diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index 0e59e95a96d9..d95dfe16b624 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -1114,6 +1114,9 @@ void ceph_handle_snap(struct ceph_mds_client *mdsc,
                                  continue;
                          adjust_snap_realm_parent(mdsc, child, realm->ino);
                  }
+       } else {
+               p += sizeof(u64) * num_split_inos;
+               p += sizeof(u64) * num_split_realms;
          }

          /*
--
2.40.1

Hi Xiubo,

This code appears to be very old -- it goes back to the initial commit
963b61eb041e ("ceph: snapshot management") in 2009.  Do you have an
explanation for why this popped up only now?
As I remembered we hit this before in one cu BZ last year, but I
couldn't remember exactly which one.  But I am not sure whether @Jeff
saw this before I joint ceph team.


Has MDS always been including split_inos and split_realms arrays in
!CEPH_SNAP_OP_SPLIT case or is this a recent change?  If it's a recent
change, I'd argue that this needs to be addressed on the MDS side.
While in MDS side for the _UPDATE op it won't send the 'split_realm'
list just before the commit in 2017:

commit 93e7267757508520dfc22cff1ab20558bd4a44d4
Author: Yan, Zheng <zyan@xxxxxxxxxx>
Date:   Fri Jul 21 21:40:46 2017 +0800

      mds: send snap related messages centrally during mds recovery

      sending CEPH_SNAP_OP_SPLIT and CEPH_SNAP_OP_UPDATE messages to
      clients centrally in MDCache::open_snaprealms()

      Signed-off-by: "Yan, Zheng" <zyan@xxxxxxxxxx>

Before this commit it will only send the 'split_realm' list for the
_SPLIT op.
It sounds like we have the culprit.  This should be treated as
a regression and fixed on the MDS side.  I don't see a justification
for putting useless data on the wire.

But we still need this patch to make it to work with the old ceph releases.

Thanks

- Xiubo

Thanks,

                 Ilya





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