linux/fs/pstore
Kees Cook 3a7d2fd16c pstore: Solve lockdep warning by moving inode locks
Lockdep complains about a possible deadlock between mount and unlink
(which is technically impossible), but fixing this improves possible
future multiple-backend support, and keeps locking in the right order.

The lockdep warning could be triggered by unlinking a file in the
pstore filesystem:

  -> #1 (&sb->s_type->i_mutex_key#14){++++++}:
         lock_acquire+0xc9/0x220
         down_write+0x3f/0x70
         pstore_mkfile+0x1f4/0x460
         pstore_get_records+0x17a/0x320
         pstore_fill_super+0xa4/0xc0
         mount_single+0x89/0xb0
         pstore_mount+0x13/0x20
         mount_fs+0xf/0x90
         vfs_kern_mount+0x66/0x170
         do_mount+0x190/0xd50
         SyS_mount+0x90/0xd0
         entry_SYSCALL_64_fastpath+0x1c/0xb1

  -> #0 (&psinfo->read_mutex){+.+.+.}:
         __lock_acquire+0x1ac0/0x1bb0
         lock_acquire+0xc9/0x220
         __mutex_lock+0x6e/0x990
         mutex_lock_nested+0x16/0x20
         pstore_unlink+0x3f/0xa0
         vfs_unlink+0xb5/0x190
         do_unlinkat+0x24c/0x2a0
         SyS_unlinkat+0x16/0x30
         entry_SYSCALL_64_fastpath+0x1c/0xb1

  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(&sb->s_type->i_mutex_key#14);
                                lock(&psinfo->read_mutex);
                                lock(&sb->s_type->i_mutex_key#14);
   lock(&psinfo->read_mutex);

Reported-by: Marta Lofstedt <marta.lofstedt@intel.com>
Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
2017-04-27 20:35:34 -07:00
..
ftrace.c pstore: Remove write_buf() callback 2017-03-07 14:01:02 -08:00
inode.c pstore: Solve lockdep warning by moving inode locks 2017-04-27 20:35:34 -07:00
internal.h pstore: Solve lockdep warning by moving inode locks 2017-04-27 20:35:34 -07:00
Kconfig docs: fix locations of several documents that got moved 2016-10-24 08:12:35 -02:00
Makefile pstore: add pstore unregister 2015-10-22 08:59:18 -07:00
platform.c pstore: Solve lockdep warning by moving inode locks 2017-04-27 20:35:34 -07:00
pmsg.c pstore: Remove unused vmalloc.h in pmsg 2017-04-27 14:48:59 -07:00
ram_core.c pstore: Use dynamic spinlock initializer 2017-03-07 08:21:38 -08:00
ram.c pstore: Remove write_buf() callback 2017-03-07 14:01:02 -08:00