On Tue, Jan 5, 2021 at 8:47 AM Amir Goldstein amir73il@gmail.com wrote:
On Tue, Jan 5, 2021 at 2:36 AM Icenowy Zheng icenowy@aosc.io wrote:
The function ovl_dir_real_file() currently uses the semaphore of the inode to synchronize write to the upperfile cache field.
Although the inode lock is a rw_sem it is referred to as the "inode lock" and you also left semaphore in the commit subject. No need to re-post. This can be fixed on commit.
However, this function will get called by ovl_ioctl_set_flags(), which utilizes the inode semaphore too. In this case ovl_dir_real_file() will try to claim a lock that is owned by a function in its call stack, which won't get released before ovl_dir_real_file() returns.
Define a dedicated semaphore for the upperfile cache, so that the deadlock won't happen.
Fixes: 61536bed2149 ("ovl: support [S|G]ETFLAGS and FS[S|G]ETXATTR ioctls for directories") Cc: stable@vger.kernel.org # v5.10 Signed-off-by: Icenowy Zheng icenowy@aosc.io
Changes in v2:
- Fixed missing replacement in error handling path.
Changes in v3:
- Use mutex instead of semaphore.
fs/overlayfs/readdir.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c index 01620ebae1bd..3980f9982f34 100644 --- a/fs/overlayfs/readdir.c +++ b/fs/overlayfs/readdir.c @@ -56,6 +56,7 @@ struct ovl_dir_file { struct list_head *cursor; struct file *realfile; struct file *upperfile;
struct mutex upperfile_mutex;That's a very specific name. This mutex protects members of struct ovl_dir_file, which could evolve into struct ovl_file one day (because no reason to cache only dir upper file), so I would go with a more generic name, but let's leave it to Miklos to decide.
He could have a different idea altogether for fixing this bug.
Miklos,
Please fast track this or an alternative fix. It fixes an easy to reproduce deadlock introduced in 5.10. Icenowy Zheng has written a simple xfstest reproducer, but it wasn't posted - best to avoid hanging tester's machines until a fix is merged...
Thanks, Amir.