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| author | Sage Weil <sage@newdream.net> | 2010-05-11 20:56:31 -0700 |
|---|---|---|
| committer | Sage Weil <sage@newdream.net> | 2010-05-11 20:56:31 -0700 |
| commit | f818a73674c5d197f66b636a46d7d578d7258129 (patch) | |
| tree | 90c485b5ca0a211b84ad8feddfce4f301de3d5c9 /fs/ceph | |
| parent | 45c6ceb547ad2d98215351974a4686bf8cb13e14 (diff) | |
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ceph: fix cap removal races
The iterate_session_caps helper traverses the session caps list and tries
to grab an inode reference. However, the __ceph_remove_cap was clearing
the inode backpointer _before_ removing itself from the session list,
causing a null pointer dereference.
Clear cap->ci under protection of s_cap_lock to avoid the race, and to
tightly couple the list and backpointer state. Use a local flag to
indicate whether we are releasing the cap, as cap->session may be modified
by a racing thread in iterate_session_caps.
Signed-off-by: Sage Weil <sage@newdream.net>
Diffstat (limited to 'fs/ceph')
| -rw-r--r-- | fs/ceph/caps.c | 19 | ||||
| -rw-r--r-- | fs/ceph/mds_client.c | 5 |
2 files changed, 15 insertions, 9 deletions
diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c index 0c16818..d940053 100644 --- a/fs/ceph/caps.c +++ b/fs/ceph/caps.c @@ -858,6 +858,8 @@ static int __ceph_is_any_caps(struct ceph_inode_info *ci) } /* + * Remove a cap. Take steps to deal with a racing iterate_session_caps. + * * caller should hold i_lock. * caller will not hold session s_mutex if called from destroy_inode. */ @@ -866,15 +868,10 @@ void __ceph_remove_cap(struct ceph_cap *cap) struct ceph_mds_session *session = cap->session; struct ceph_inode_info *ci = cap->ci; struct ceph_mds_client *mdsc = &ceph_client(ci->vfs_inode.i_sb)->mdsc; + int removed = 0; dout("__ceph_remove_cap %p from %p\n", cap, &ci->vfs_inode); - /* remove from inode list */ - rb_erase(&cap->ci_node, &ci->i_caps); - cap->ci = NULL; - if (ci->i_auth_cap == cap) - ci->i_auth_cap = NULL; - /* remove from session list */ spin_lock(&session->s_cap_lock); if (session->s_cap_iterator == cap) { @@ -885,10 +882,18 @@ void __ceph_remove_cap(struct ceph_cap *cap) list_del_init(&cap->session_caps); session->s_nr_caps--; cap->session = NULL; + removed = 1; } + /* protect backpointer with s_cap_lock: see iterate_session_caps */ + cap->ci = NULL; spin_unlock(&session->s_cap_lock); - if (cap->session == NULL) + /* remove from inode list */ + rb_erase(&cap->ci_node, &ci->i_caps); + if (ci->i_auth_cap == cap) + ci->i_auth_cap = NULL; + + if (removed) ceph_put_cap(cap); if (!__ceph_is_any_caps(ci) && ci->i_snap_realm) { diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c index eccc0ec..24561a5 100644 --- a/fs/ceph/mds_client.c +++ b/fs/ceph/mds_client.c @@ -736,9 +736,10 @@ static void cleanup_cap_releases(struct ceph_mds_session *session) } /* - * Helper to safely iterate over all caps associated with a session. + * Helper to safely iterate over all caps associated with a session, with + * special care taken to handle a racing __ceph_remove_cap(). * - * caller must hold session s_mutex + * Caller must hold session s_mutex. */ static int iterate_session_caps(struct ceph_mds_session *session, int (*cb)(struct inode *, struct ceph_cap *, |