Detaching of mark connector from fsnotify_put_mark() can race with unmounting of the filesystem like:
CPU1 CPU2 fsnotify_put_mark() spin_lock(&conn->lock); ... inode = fsnotify_detach_connector_from_object(conn) spin_unlock(&conn->lock); generic_shutdown_super() fsnotify_unmount_inodes() sees connector detached for inode -> nothing to do evict_inode() barfs on pending inode reference iput(inode);
Resulting in "Busy inodes after unmount" message and possible kernel oops. Make fsnotify_unmount_inodes() properly wait for outstanding inode references from detached connectors.
Note that the accounting of outstanding inode references in the superblock can cause some cacheline contention on the counter. OTOH it happens only during deletion of the last notification mark from an inode (or during unlinking of watched inode) and that is not too bad. I have measured time to create & delete inotify watch 100000 times from 64 processes in parallel (each process having its own inotify group and its own file on a shared superblock) on a 64 CPU machine. Average and standard deviation of 15 runs look like:
Avg Stddev Vanilla 9.817400 0.276165 Fixed 9.710467 0.228294
So there's no statistically significant difference.
Fixes: 6b3f05d24d35 ("fsnotify: Detach mark from object list when last reference is dropped") CC: stable@vger.kernel.org Signed-off-by: Jan Kara jack@suse.cz --- fs/notify/fsnotify.c | 3 +++ fs/notify/mark.c | 39 +++++++++++++++++++++++++++++++-------- include/linux/fs.h | 3 +++ 3 files changed, 37 insertions(+), 8 deletions(-)
Changes since v2: * fixed uninitialized warning
Changes since v1: * added Fixes tag * fsnotify_drop_object() now takes type
diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c index f174397b63a0..00d4f4357724 100644 --- a/fs/notify/fsnotify.c +++ b/fs/notify/fsnotify.c @@ -96,6 +96,9 @@ void fsnotify_unmount_inodes(struct super_block *sb)
if (iput_inode) iput(iput_inode); + /* Wait for outstanding inode references from connectors */ + wait_var_event(&sb->s_fsnotify_inode_refs, + !atomic_long_read(&sb->s_fsnotify_inode_refs)); }
/* diff --git a/fs/notify/mark.c b/fs/notify/mark.c index 59cdb27826de..09535f6423fc 100644 --- a/fs/notify/mark.c +++ b/fs/notify/mark.c @@ -179,17 +179,20 @@ static void fsnotify_connector_destroy_workfn(struct work_struct *work) } }
-static struct inode *fsnotify_detach_connector_from_object( - struct fsnotify_mark_connector *conn) +static void *fsnotify_detach_connector_from_object( + struct fsnotify_mark_connector *conn, + unsigned int *type) { struct inode *inode = NULL;
+ *type = conn->type; if (conn->type == FSNOTIFY_OBJ_TYPE_DETACHED) return NULL;
if (conn->type == FSNOTIFY_OBJ_TYPE_INODE) { inode = fsnotify_conn_inode(conn); inode->i_fsnotify_mask = 0; + atomic_long_inc(&inode->i_sb->s_fsnotify_inode_refs); } else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT) { fsnotify_conn_mount(conn)->mnt_fsnotify_mask = 0; } @@ -211,10 +214,29 @@ static void fsnotify_final_mark_destroy(struct fsnotify_mark *mark) fsnotify_put_group(group); }
+/* Drop object reference originally held by a connector */ +static void fsnotify_drop_object(unsigned int type, void *objp) +{ + struct inode *inode; + struct super_block *sb; + + if (!objp) + return; + /* Currently only inode references are passed to be dropped */ + if (WARN_ON_ONCE(type != FSNOTIFY_OBJ_TYPE_INODE)) + return; + inode = objp; + sb = inode->i_sb; + iput(inode); + if (atomic_long_dec_and_test(&sb->s_fsnotify_inode_refs)) + wake_up_var(&sb->s_fsnotify_inode_refs); +} + void fsnotify_put_mark(struct fsnotify_mark *mark) { struct fsnotify_mark_connector *conn; - struct inode *inode = NULL; + void *objp = NULL; + unsigned int type = FSNOTIFY_OBJ_TYPE_DETACHED; bool free_conn = false;
/* Catch marks that were actually never attached to object */ @@ -234,7 +256,7 @@ void fsnotify_put_mark(struct fsnotify_mark *mark) conn = mark->connector; hlist_del_init_rcu(&mark->obj_list); if (hlist_empty(&conn->list)) { - inode = fsnotify_detach_connector_from_object(conn); + objp = fsnotify_detach_connector_from_object(conn, &type); free_conn = true; } else { __fsnotify_recalc_mask(conn); @@ -242,7 +264,7 @@ void fsnotify_put_mark(struct fsnotify_mark *mark) mark->connector = NULL; spin_unlock(&conn->lock);
- iput(inode); + fsnotify_drop_object(type, objp);
if (free_conn) { spin_lock(&destroy_lock); @@ -709,7 +731,8 @@ void fsnotify_destroy_marks(fsnotify_connp_t *connp) { struct fsnotify_mark_connector *conn; struct fsnotify_mark *mark, *old_mark = NULL; - struct inode *inode; + void *objp; + unsigned int type;
conn = fsnotify_grab_connector(connp); if (!conn) @@ -735,11 +758,11 @@ void fsnotify_destroy_marks(fsnotify_connp_t *connp) * mark references get dropped. It would lead to strange results such * as delaying inode deletion or blocking unmount. */ - inode = fsnotify_detach_connector_from_object(conn); + objp = fsnotify_detach_connector_from_object(conn, &type); spin_unlock(&conn->lock); if (old_mark) fsnotify_put_mark(old_mark); - iput(inode); + fsnotify_drop_object(type, objp); }
/* diff --git a/include/linux/fs.h b/include/linux/fs.h index 33322702c910..5090f3dcec3b 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1428,6 +1428,9 @@ struct super_block { /* Number of inodes with nlink == 0 but still referenced */ atomic_long_t s_remove_count;
+ /* Pending fsnotify inode refs */ + atomic_long_t s_fsnotify_inode_refs; + /* Being remounted read-only */ int s_readonly_remount;