Re: [PATCH] ceph: clear `s_cap_reconnect` when ceph_pagelist_encode_32() fails

[Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>]

On Mon, 2026-03-30 at 10:43 +0200, Max Kellermann wrote:
> This MDS reconnect error path leaves s_cap_reconnect set.
> send_mds_reconnect() sets the bit at the beginning of the reconnect,
> but the first failing operation after that, ceph_pagelist_encode_32(),
> can jump to `fail:` without clearing it.
> 
> __ceph_remove_cap() consults that flag to decide whether cap releases
> should be queued. A reconnect-preparation failure therefore leaves the
> session in reconnect mode from the cap-release path's point of view
> and can strand release work until some later state transition repairs
> it.
> 
> Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
> ---
>  fs/ceph/mds_client.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
> index b1746273f186..4fa471d9b3b2 100644
> --- a/fs/ceph/mds_client.c
> +++ b/fs/ceph/mds_client.c
> @@ -4956,7 +4956,7 @@ static void send_mds_reconnect(struct ceph_mds_client *mdsc,
>  	/* placeholder for nr_caps */
>  	err = ceph_pagelist_encode_32(recon_state.pagelist, 0);
>  	if (err)
> -		goto fail;
> +		goto fail_clear_cap_reconnect;
>  
>  	if (test_bit(CEPHFS_FEATURE_MULTI_RECONNECT, &session->s_features)) {
>  		recon_state.msg_version = 3;
> @@ -5046,6 +5046,10 @@ static void send_mds_reconnect(struct ceph_mds_client *mdsc,
>  	ceph_pagelist_release(recon_state.pagelist);
>  	return;
>  
> +fail_clear_cap_reconnect:
> +	spin_lock(&session->s_cap_lock);
> +	session->s_cap_reconnect = 0;
> +	spin_unlock(&session->s_cap_lock);
>  fail:
>  	ceph_msg_put(reply);
>  	up_read(&mdsc->snap_rwsem);

Makes sense. Nice fix. But, maybe, we need to consider refactoring of this
function because of such issue.

Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>

Thanks,
Slava.