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

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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.

Thanks,

                Ilya




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