Re: [PATCH v3] ovl: use a dedicated semaphore for dir upperfile caching
From: Amir Goldstein <amir73il@gmail.com>
Date: 2021-01-05 06:48:34
Also in:
linux-unionfs, lkml
On Tue, Jan 5, 2021 at 2:36 AM Icenowy Zheng [off-list ref] 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.
quoted hunk ↗ jump to hunk
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. Thanks, Amir.