[PATCH] ceph: check session state after bumping session->s_seq

[PATCH] ceph: check session state after bumping session->s_seq

[Jeff Layton]

Some messages sent by the MDS entail a session sequence number
increment, and the MDS will drop certain types of requests on the floor
when the sequence numbers don't match.

In particular, a REQUEST_CLOSE message can cross with one of sequence
morphing messages from the MDS, which can cause the client to stall,
waiting for a response that will never come.

Originally, this meant an up to 5s delay before the recurring workqueue
job kicked in and resent the request, but a recent change made it so
that the client would never resend, causing a 60s stall unmounting and
sometimes a blockisting event.

Fix this by checking the connection state after bumping the session
sequence, which should cause a retransmit of the REQUEST_CLOSE, when
this occurs.

URL: https://tracker.ceph.com/issues/47563
Fixes: fa9967734227 ("ceph: fix potential mdsc use-after-free crash")
Reported-by: Patrick Donnelly <pdonnell@redhat.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/ceph/caps.c       | 1 +
 fs/ceph/mds_client.c | 1 +
 fs/ceph/quota.c      | 1 +
 fs/ceph/snap.c       | 1 +
 4 files changed, 4 insertions(+)

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index c00abd7eefc1..ac822c74baea 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -4072,6 +4072,7 @@ void ceph_handle_caps(struct ceph_mds_session *session,
 
 	mutex_lock(&session->s_mutex);
 	session->s_seq++;
+	check_session_state(session);
 	dout(" mds%d seq %lld cap seq %u\n", session->s_mds, session->s_seq,
 	     (unsigned)seq);
 
diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 0190555b1f9e..69f529d894e6 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -4238,6 +4238,7 @@ static void handle_lease(struct ceph_mds_client *mdsc,
 
 	mutex_lock(&session->s_mutex);
 	session->s_seq++;
+	check_session_state(session);
 
 	if (!inode) {
 		dout("handle_lease no inode %llx\n", vino.ino);
diff --git a/fs/ceph/quota.c b/fs/ceph/quota.c
index 83cb4f26b689..a09667ee83c1 100644
--- a/fs/ceph/quota.c
+++ b/fs/ceph/quota.c
@@ -54,6 +54,7 @@ void ceph_handle_quota(struct ceph_mds_client *mdsc,
 	/* increment msg sequence number */
 	mutex_lock(&session->s_mutex);
 	session->s_seq++;
+	check_session_state(session);
 	mutex_unlock(&session->s_mutex);
 
 	/* lookup inode */
diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index 0da39c16dab4..f1e73a65f4a5 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -874,6 +874,7 @@ void ceph_handle_snap(struct ceph_mds_client *mdsc,
 
 	mutex_lock(&session->s_mutex);
 	session->s_seq++;
+	check_session_state(session);
 	mutex_unlock(&session->s_mutex);
 
 	down_write(&mdsc->snap_rwsem);
-- 
2.26.2

Re: [PATCH] ceph: check session state after bumping session->s_seq

[Ilya Dryomov]

On Mon, Oct 12, 2020 at 5:13 PM Jeff Layton <jlayton@kernel.org> wrote:
>
> Some messages sent by the MDS entail a session sequence number
> increment, and the MDS will drop certain types of requests on the floor
> when the sequence numbers don't match.
>
> In particular, a REQUEST_CLOSE message can cross with one of sequence
> morphing messages from the MDS, which can cause the client to stall,
> waiting for a response that will never come.
>
> Originally, this meant an up to 5s delay before the recurring workqueue
> job kicked in and resent the request, but a recent change made it so
> that the client would never resend, causing a 60s stall unmounting and
> sometimes a blockisting event.
>
> Fix this by checking the connection state after bumping the session
> sequence, which should cause a retransmit of the REQUEST_CLOSE, when
> this occurs.
>
> URL: https://tracker.ceph.com/issues/47563
> Fixes: fa9967734227 ("ceph: fix potential mdsc use-after-free crash")
> Reported-by: Patrick Donnelly <pdonnell@redhat.com>
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>  fs/ceph/caps.c       | 1 +
>  fs/ceph/mds_client.c | 1 +
>  fs/ceph/quota.c      | 1 +
>  fs/ceph/snap.c       | 1 +
>  4 files changed, 4 insertions(+)
>
> diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
> index c00abd7eefc1..ac822c74baea 100644
> --- a/fs/ceph/caps.c
> +++ b/fs/ceph/caps.c
> @@ -4072,6 +4072,7 @@ void ceph_handle_caps(struct ceph_mds_session *session,
>
>         mutex_lock(&session->s_mutex);
>         session->s_seq++;
> +       check_session_state(session);
>         dout(" mds%d seq %lld cap seq %u\n", session->s_mds, session->s_seq,
>              (unsigned)seq);
>
> diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
> index 0190555b1f9e..69f529d894e6 100644
> --- a/fs/ceph/mds_client.c
> +++ b/fs/ceph/mds_client.c
> @@ -4238,6 +4238,7 @@ static void handle_lease(struct ceph_mds_client *mdsc,
>
>         mutex_lock(&session->s_mutex);
>         session->s_seq++;
> +       check_session_state(session);
>
>         if (!inode) {
>                 dout("handle_lease no inode %llx\n", vino.ino);
> diff --git a/fs/ceph/quota.c b/fs/ceph/quota.c
> index 83cb4f26b689..a09667ee83c1 100644
> --- a/fs/ceph/quota.c
> +++ b/fs/ceph/quota.c
> @@ -54,6 +54,7 @@ void ceph_handle_quota(struct ceph_mds_client *mdsc,
>         /* increment msg sequence number */
>         mutex_lock(&session->s_mutex);
>         session->s_seq++;
> +       check_session_state(session);
>         mutex_unlock(&session->s_mutex);
>
>         /* lookup inode */
> diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
> index 0da39c16dab4..f1e73a65f4a5 100644
> --- a/fs/ceph/snap.c
> +++ b/fs/ceph/snap.c
> @@ -874,6 +874,7 @@ void ceph_handle_snap(struct ceph_mds_client *mdsc,
>
>         mutex_lock(&session->s_mutex);
>         session->s_seq++;
> +       check_session_state(session);
>         mutex_unlock(&session->s_mutex);
>
>         down_write(&mdsc->snap_rwsem);
> --
> 2.26.2
>

A new helper just for

   if (s->s_state == CEPH_MDS_SESSION_CLOSING) {
           dout("resending session close request for mds%d\n",
                           s->s_mds);
           request_close_session(s);
   }

would be more precise IMO.  It could check request_close_session()
return value and log the error, too.

Thanks,

                Ilya