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Get rid of lockdep false positives around sysfs/overlayfs

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Merge tag 'pull-sysfs-annotation-fix' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

Pull sysfs fix from Al Viro:
 "Get rid of lockdep false positives around sysfs/overlayfs

  syzbot has uncovered a class of lockdep false positives for setups
  with sysfs being one of the backing layers in overlayfs. The root
  cause is that of->mutex allocated when opening a sysfs file read-only
  (which overlayfs might do) is confused with of->mutex of a file opened
  writable (held in write to sysfs file, which overlayfs won't do).

  Assigning them separate lockdep classes fixes that bunch and it's
  obviously safe"

* tag 'pull-sysfs-annotation-fix' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  kernfs: annotate different lockdep class for of->mutex of writable files
This commit is contained in:
Linus Torvalds 2024-04-14 11:41:51 -07:00
commit 72374d71c3
1 changed files with 8 additions and 1 deletions
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9
fs/kernfs/file.c
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@ -636,11 +636,18 @@ static int kernfs_fop_open(struct inode *inode, struct file *file)
* each file a separate locking class. Let's differentiate on
* whether the file has mmap or not for now.
*
* Both paths of the branch look the same. They're supposed to
* For similar reasons, writable and readonly files are given different
* lockdep key, because the writable file /sys/power/resume may call vfs
* lookup helpers for arbitrary paths and readonly files can be read by
* overlayfs from vfs helpers when sysfs is a lower layer of overalyfs.
*
* All three cases look the same. They're supposed to
* look that way and give @of->mutex different static lockdep keys.
*/
if (has_mmap)
mutex_init(&of->mutex);
else if (file->f_mode & FMODE_WRITE)
mutex_init(&of->mutex);
else
mutex_init(&of->mutex);