linux/fs/notify
Jerry Hoemann 6424babfd6 fsnotify: next_i is freed during fsnotify_unmount_inodes.
During file system stress testing on 3.10 and 3.12 based kernels, the
umount command occasionally hung in fsnotify_unmount_inodes in the
section of code:

                spin_lock(&inode->i_lock);
                if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) {
                        spin_unlock(&inode->i_lock);
                        continue;
                }

As this section of code holds the global inode_sb_list_lock, eventually
the system hangs trying to acquire the lock.

Multiple crash dumps showed:

The inode->i_state == 0x60 and i_count == 0 and i_sb_list would point
back at itself.  As this is not the value of list upon entry to the
function, the kernel never exits the loop.

To help narrow down problem, the call to list_del_init in
inode_sb_list_del was changed to list_del.  This poisons the pointers in
the i_sb_list and causes a kernel to panic if it transverse a freed
inode.

Subsequent stress testing paniced in fsnotify_unmount_inodes at the
bottom of the list_for_each_entry_safe loop showing next_i had become
free.

We believe the root cause of the problem is that next_i is being freed
during the window of time that the list_for_each_entry_safe loop
temporarily releases inode_sb_list_lock to call fsnotify and
fsnotify_inode_delete.

The code in fsnotify_unmount_inodes attempts to prevent the freeing of
inode and next_i by calling __iget.  However, the code doesn't do the
__iget call on next_i

	if i_count == 0 or
	if i_state & (I_FREEING | I_WILL_FREE)

The patch addresses this issue by advancing next_i in the above two cases
until we either find a next_i which we can __iget or we reach the end of
the list.  This makes the handling of next_i more closely match the
handling of the variable "inode."

The time to reproduce the hang is highly variable (from hours to days.) We
ran the stress test on a 3.10 kernel with the proposed patch for a week
without failure.

During list_for_each_entry_safe, next_i is becoming free causing
the loop to never terminate.  Advance next_i in those cases where
__iget is not done.

Signed-off-by: Jerry Hoemann <jerry.hoemann@hp.com>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Cc: Ken Helias <kenhelias@firemail.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-29 16:33:14 -07:00
..
dnotify security: make security_file_set_fowner, f_setown and __f_setown void return 2014-09-09 16:01:36 -04:00
fanotify fanotify: enable close-on-exec on events' fd when requested in fanotify_init() 2014-10-09 22:25:46 -04:00
inotify fsnotify: don't put user context if it was never assigned 2014-10-09 22:25:45 -04:00
Kconfig fanotify: allow fanotify to be built 2010-10-28 17:22:13 -04:00
Makefile fs, notify: add procfs fdinfo helper 2012-12-17 17:15:28 -08:00
fdinfo.c fs/notify: don't show f_handle if exportfs_encode_inode_fh failed 2014-09-10 15:42:12 -07:00
fdinfo.h fs, notify: add procfs fdinfo helper 2012-12-17 17:15:28 -08:00
fsnotify.c inotify: Fix reporting of cookies for inotify events 2014-02-18 11:17:17 +01:00
fsnotify.h fs/notify/group.c: make fsnotify_final_destroy_group() static 2014-10-09 22:25:45 -04:00
group.c fs/notify/group.c: make fsnotify_final_destroy_group() static 2014-10-09 22:25:45 -04:00
inode_mark.c fsnotify: next_i is freed during fsnotify_unmount_inodes. 2014-10-29 16:33:14 -07:00
mark.c fs/notify/mark.c: trivial cleanup 2014-06-04 16:53:52 -07:00
notification.c fanotify: fix double free of pending permission events 2014-08-06 18:01:12 -07:00
vfsmount_mark.c list: fix order of arguments for hlist_add_after(_rcu) 2014-08-06 18:01:24 -07:00