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Commit d8fb02ab authored by Alex Elder's avatar Alex Elder Committed by Sage Weil
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ceph: create a new session lock to avoid lock inversion 



Lockdep was reporting a possible circular lock dependency in
dentry_lease_is_valid().  That function needs to sample the
session's s_cap_gen and and s_cap_ttl fields coherently, but needs
to do so while holding a dentry lock.  The s_cap_lock field was
being used to protect the two fields, but that can't be taken while
holding a lock on a dentry within the session.

In most cases, the s_cap_gen and s_cap_ttl fields only get operated
on separately.  But in three cases they need to be updated together.
Implement a new lock to protect the spots updating both fields
atomically is required.

Signed-off-by: default avatarAlex Elder <elder@dreamhost.com>
Reviewed-by: default avatarSage Weil <sage@newdream.net>
parent 32852a81

fs/ceph/caps.c

+2 −2
Original line number Diff line number Diff line
@@ -641,10 +641,10 @@ static int __cap_is_valid(struct ceph_cap *cap) 
	unsigned long ttl;

	u32 gen;



	spin_lock(&cap->session->s_cap_lock);

	spin_lock(&cap->session->s_gen_ttl_lock);

	gen = cap->session->s_cap_gen;

	ttl = cap->session->s_cap_ttl;

	spin_unlock(&cap->session->s_cap_lock);

	spin_unlock(&cap->session->s_gen_ttl_lock);



	if (cap->cap_gen < gen || time_after_eq(jiffies, ttl)) {

		dout("__cap_is_valid %p cap %p issued %s "

fs/ceph/dir.c

+2 −2
Original line number Diff line number Diff line
@@ -975,10 +975,10 @@ static int dentry_lease_is_valid(struct dentry *dentry) 
	di = ceph_dentry(dentry);

	if (di && di->lease_session) {

		s = di->lease_session;

		spin_lock(&s->s_cap_lock);

		spin_lock(&s->s_gen_ttl_lock);

		gen = s->s_cap_gen;

		ttl = s->s_cap_ttl;

		spin_unlock(&s->s_cap_lock);

		spin_unlock(&s->s_gen_ttl_lock);



		if (di->lease_gen == gen &&

		    time_before(jiffies, dentry->d_time) &&

fs/ceph/mds_client.c

+5 −3
Original line number Diff line number Diff line
@@ -400,9 +400,11 @@ static struct ceph_mds_session *register_session(struct ceph_mds_client *mdsc, 
	s->s_con.peer_name.type = CEPH_ENTITY_TYPE_MDS;

	s->s_con.peer_name.num = cpu_to_le64(mds);



	spin_lock_init(&s->s_cap_lock);

	spin_lock_init(&s->s_gen_ttl_lock);

	s->s_cap_gen = 0;

	s->s_cap_ttl = 0;



	spin_lock_init(&s->s_cap_lock);

	s->s_renew_requested = 0;

	s->s_renew_seq = 0;

	INIT_LIST_HEAD(&s->s_caps);
@@ -2328,10 +2330,10 @@ static void handle_session(struct ceph_mds_session *session, 
	case CEPH_SESSION_STALE:

		pr_info("mds%d caps went stale, renewing\n",

			session->s_mds);

		spin_lock(&session->s_cap_lock);

		spin_lock(&session->s_gen_ttl_lock);

		session->s_cap_gen++;

		session->s_cap_ttl = 0;

		spin_unlock(&session->s_cap_lock);

		spin_unlock(&session->s_gen_ttl_lock);

		send_renew_caps(mdsc, session);

		break;

fs/ceph/mds_client.h

+5 −2
Original line number Diff line number Diff line
@@ -117,10 +117,13 @@ struct ceph_mds_session { 
	void             *s_authorizer_buf, *s_authorizer_reply_buf;

	size_t            s_authorizer_buf_len, s_authorizer_reply_buf_len;



	/* protected by s_cap_lock */

	spinlock_t        s_cap_lock;

	/* protected by s_gen_ttl_lock */

	spinlock_t        s_gen_ttl_lock;

	u32               s_cap_gen;  /* inc each time we get mds stale msg */

	unsigned long     s_cap_ttl;  /* when session caps expire */



	/* protected by s_cap_lock */

	spinlock_t        s_cap_lock;

	struct list_head  s_caps;     /* all caps issued by this session */

	int               s_nr_caps, s_trim_caps;

	int               s_num_cap_releases;