On Thu, 9 May 2024 17:52:21 +0300 Amir Goldstein <amir73il@xxxxxxxxx>
> On Thu, May 9, 2024 at 1:49 PM Hillf Danton <hdanton@xxxxxxxx> wrote:
> >
> > The correct locking order is
> >
> > sb_writers
>
> This is sb of overlayfs
>
> > inode lock
>
> This is real inode
>
WRT sb_writers the order
lock inode parent
lock inode kid
becomes
lock inode kid
sb_writers
lock inode parent
given call trace
> -> #2 (sb_writers#4){.+.+}-{0:0}:
> lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
> percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
> __sb_start_write include/linux/fs.h:1664 [inline]
> sb_start_write+0x4d/0x1c0 include/linux/fs.h:1800
> mnt_want_write+0x3f/0x90 fs/namespace.c:409
> ovl_create_object+0x13b/0x370 fs/overlayfs/dir.c:629
> lookup_open fs/namei.c:3497 [inline]
> open_last_lookups fs/namei.c:3566 [inline]
and code snippet [1]
if (open_flag & O_CREAT)
inode_lock(dir->d_inode);
else
inode_lock_shared(dir->d_inode);
dentry = lookup_open(nd, file, op, got_write);
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/namei.c?id=dccb07f2914c#n3566
