[PATCH 5.9 064/255] ceph: check session state after bumping session->s_seq

Greg Kroah-Hartman
2020-11-17T13:49:07Z

From: Jeff Layton <jlayton@kernel.org>

[ Upstream commit 62575e270f661aba64778cbc5f354511cf9abb21 ]

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).

[ idryomov: whitespace, pr_err() call fixup ]

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>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/ceph/caps.c | 2 +-
fs/ceph/mds_client.c | 50 +++++++++++++++++++++++++++++++-------------
fs/ceph/mds_client.h | 1 +
fs/ceph/quota.c | 2 +-
fs/ceph/snap.c | 2 +-
5 files changed, 39 insertions(+), 18 deletions(-)

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index 034b3f4fdd3a7..64a64a29f5c79 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -4064,7 +4064,7 @@ 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 76d8d9495d1d4..b2214679baf4e 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -4227,7 +4227,7 @@ 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);
@@ -4381,28 +4381,48 @@ 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("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 658800605bfb4..11f20a4d36bc5 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 cc2c4d40b0222..2b213f864c564 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 923be9399b21c..cc9a9bfc790a3 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);
--
2.27.0