WSL2-Linux-Kernel/fs/notify
Jan Kara 721fb6fbfd fsnotify: Fix busy inodes during unmount
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: 6b3f05d24d ("fsnotify: Detach mark from object list when last reference is dropped")
CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
2018-10-25 15:49:19 +02:00
..
dnotify Merge branch 'siginfo-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2018-08-21 13:47:29 -07:00
fanotify fanotify: support reporting thread id instead of process id 2018-10-08 13:48:45 +02:00
inotify fsnotify: convert runtime BUG_ON() to BUILD_BUG_ON() 2018-10-04 13:28:50 +02:00
Kconfig rcu: Make SRCU optional by using CONFIG_SRCU 2015-01-06 11:04:29 -08:00
Makefile License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
fdinfo.c fanotify: store fanotify_init() flags in group's fanotify_data 2018-09-27 15:29:00 +02:00
fdinfo.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
fsnotify.c fsnotify: Fix busy inodes during unmount 2018-10-25 15:49:19 +02:00
fsnotify.h fsnotify: add super block object type 2018-09-03 15:14:01 +02:00
group.c fs: fsnotify: account fsnotify metadata to kmemcg 2018-08-17 16:20:30 -07:00
mark.c fsnotify: Fix busy inodes during unmount 2018-10-25 15:49:19 +02:00
notification.c fsnotify: Let userspace know about lost events due to ENOMEM 2018-02-27 10:25:33 +01:00