linux-kernel - Re: [PATCH] libceph: Reset sparse-read on fault

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Message-ID: <CAOi1vP8WvK-0nGjKY6ss2MX6ZjvDOhcur5SyM=E=uipW0fy76g@mail.gmail.com>
Date: Mon, 5 Jan 2026 13:51:47 +0100
From: Ilya Dryomov <idryomov@...il.com>
To: Sam Edwards <cfsworks@...il.com>
Cc: Xiubo Li <xiubli@...hat.com>, ceph-devel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] libceph: Reset sparse-read on fault

On Wed, Dec 31, 2025 at 5:05 AM Sam Edwards <cfsworks@...il.com> wrote:
>
> When a fault occurs, the connection is abandoned, reestablished, and any
> pending operations are retried. The OSD client tracks the progress of a
> sparse-read reply using a separate state machine, largely independent of
> the messenger's state.
>
> If a connection is lost mid-payload or the sparse-read state machine
> returns an error, the sparse-read state is not reset. The OSD client
> will then interpret the beginning of a new reply as the continuation of
> the old one. If this makes the sparse-read machinery enter a failure
> state, it may never recover, producing loops like:
>
>   libceph:  [0] got 0 extents
>   libceph: data len 142248331 != extent len 0
>   libceph: osd0 (1)...:6801 socket error on read
>   libceph: data len 142248331 != extent len 0
>   libceph: osd0 (1)...:6801 socket error on read
>
> Therefore, reset the sparse-read state in osd_fault(), ensuring retries
> start from a clean state.
>
> Cc: stable@...r.kernel.org
> Signed-off-by: Sam Edwards <CFSworks@...il.com>
> ---
>  net/ceph/osd_client.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/net/ceph/osd_client.c b/net/ceph/osd_client.c
> index 3667319b949d..1a7be2f615dc 100644
> --- a/net/ceph/osd_client.c
> +++ b/net/ceph/osd_client.c
> @@ -4281,6 +4281,9 @@ static void osd_fault(struct ceph_connection *con)
>                 goto out_unlock;
>         }
>
> +       osd->o_sparse_op_idx = -1;
> +       ceph_init_sparse_read(&osd->o_sparse_read);
> +
>         if (!reopen_osd(osd))
>                 kick_osd_requests(osd);
>         maybe_request_map(osdc);
> --
> 2.51.2
>

Hi Sam,

Good catch!  Applied (with the sad note that support for sparse
reads is officially the most problematic patchset that ever made it
into libceph).

Thanks,

                Ilya