Re: [PATCH v3] ceph: check session state after bumping session->s_seq

[Xiubo Li <xiubli@redhat.com>]

On 2020/10/13 20:02, Jeff Layton 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 the
> 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.
>
> Add a new helper for incrementing the session sequence and then testing
> to see whether a REQUEST_CLOSE needs to be resent, and move the handling
> of CEPH_MDS_SESSION_CLOSING into that function. Change all of the
> bare sequence counter increments to use the new helper.
>
> Reorganize check_session_state with a switch statement.  It should no
> longer be called when the session is CLOSING, so throw a warning if it
> ever is (but still handle that case sanely).
>
> 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       |  2 +-
>   fs/ceph/mds_client.c | 51 ++++++++++++++++++++++++++++++--------------
>   fs/ceph/mds_client.h |  1 +
>   fs/ceph/quota.c      |  2 +-
>   fs/ceph/snap.c       |  2 +-
>   5 files changed, 39 insertions(+), 19 deletions(-)
>
> v3: reorganize check_session_state with switch statement. Don't attempt
>      to reconnect in there, but do throw a warning if it's called while
>      the session is CLOSING.
>
> diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
> index c00abd7eefc1..ba0e4f44862c 100644
> --- a/fs/ceph/caps.c
> +++ b/fs/ceph/caps.c
> @@ -4071,7 +4071,7 @@ void ceph_handle_caps(struct ceph_mds_session *session,
>   	     vino.snap, inode);
>   
>   	mutex_lock(&session->s_mutex);
> -	session->s_seq++;
> +	inc_session_sequence(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..00c0dc33f92e 100644
> --- a/fs/ceph/mds_client.c
> +++ b/fs/ceph/mds_client.c
> @@ -4237,7 +4237,7 @@ static void handle_lease(struct ceph_mds_client *mdsc,
>   	     dname.len, dname.name);
>   
>   	mutex_lock(&session->s_mutex);
> -	session->s_seq++;
> +	inc_session_sequence(session);
>   
>   	if (!inode) {
>   		dout("handle_lease no inode %llx\n", vino.ino);
> @@ -4386,28 +4386,47 @@ static void maybe_recover_session(struct ceph_mds_client *mdsc)
>   
>   bool check_session_state(struct ceph_mds_session *s)
>   {
> -	if (s->s_state == CEPH_MDS_SESSION_CLOSING) {
> -		dout("resending session close request for mds%d\n",
> -				s->s_mds);
> -		request_close_session(s);
> -		return false;
> -	}
> -	if (s->s_ttl && time_after(jiffies, s->s_ttl)) {
> -		if (s->s_state == CEPH_MDS_SESSION_OPEN) {
> +
> +	switch (s->s_state) {
> +	case CEPH_MDS_SESSION_OPEN:
> +		if (s->s_ttl && time_after(jiffies, s->s_ttl)) {
>   			s->s_state = CEPH_MDS_SESSION_HUNG;
>   			pr_info("mds%d hung\n", s->s_mds);
>   		}
> -	}
> -	if (s->s_state == CEPH_MDS_SESSION_NEW ||
> -	    s->s_state == CEPH_MDS_SESSION_RESTARTING ||
> -	    s->s_state == CEPH_MDS_SESSION_CLOSED ||
> -	    s->s_state == CEPH_MDS_SESSION_REJECTED)
> -		/* this mds is failed or recovering, just wait */
> +		break;
> +	case CEPH_MDS_SESSION_CLOSING:
> +		/* Should never reach this when we're unmounting */
> +		WARN_ON_ONCE(true);
> +		fallthrough;
> +	case CEPH_MDS_SESSION_NEW:
> +	case CEPH_MDS_SESSION_RESTARTING:
> +	case CEPH_MDS_SESSION_CLOSED:
> +	case CEPH_MDS_SESSION_REJECTED:
>   		return false;
> -
> +	}
>   	return true;
>   }
>   
> +/*
> + * If the sequence is incremented while we're waiting on a REQUEST_CLOSE reply,
> + * then we need to retransmit that request.
> + */
> +void inc_session_sequence(struct ceph_mds_session *s)
> +{
> +	lockdep_assert_held(&s->s_mutex);
> +
> +	s->s_seq++;
> +
> +	if (s->s_state == CEPH_MDS_SESSION_CLOSING) {
> +		int ret;
> +
> +		dout("resending session close request for mds%d\n", s->s_mds);
> +		ret = request_close_session(s);
> +		if (ret < 0)
> +			pr_err("ceph: Unable to close session to mds %d: %d\n", s->s_mds, ret);
> +	}
> +}
> +
>   /*
>    * delayed work -- periodically trim expired leases, renew caps with mds
>    */
> diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
> index cbf8af437140..f5adbebcb38e 100644
> --- a/fs/ceph/mds_client.h
> +++ b/fs/ceph/mds_client.h
> @@ -480,6 +480,7 @@ struct ceph_mds_client {
>   extern const char *ceph_mds_op_name(int op);
>   
>   extern bool check_session_state(struct ceph_mds_session *s);
> +void inc_session_sequence(struct ceph_mds_session *s);
>   
>   extern struct ceph_mds_session *
>   __ceph_lookup_mds_session(struct ceph_mds_client *, int mds);
> diff --git a/fs/ceph/quota.c b/fs/ceph/quota.c
> index 83cb4f26b689..9b785f11e95a 100644
> --- a/fs/ceph/quota.c
> +++ b/fs/ceph/quota.c
> @@ -53,7 +53,7 @@ void ceph_handle_quota(struct ceph_mds_client *mdsc,
>   
>   	/* increment msg sequence number */
>   	mutex_lock(&session->s_mutex);
> -	session->s_seq++;
> +	inc_session_sequence(session);
>   	mutex_unlock(&session->s_mutex);
>   
>   	/* lookup inode */
> diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
> index 0da39c16dab4..b611f829cb61 100644
> --- a/fs/ceph/snap.c
> +++ b/fs/ceph/snap.c
> @@ -873,7 +873,7 @@ void ceph_handle_snap(struct ceph_mds_client *mdsc,
>   	     ceph_snap_op_name(op), split, trace_len);
>   
>   	mutex_lock(&session->s_mutex);
> -	session->s_seq++;
> +	inc_session_sequence(session);
>   	mutex_unlock(&session->s_mutex);
>   
>   	down_write(&mdsc->snap_rwsem);

LGTM.