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Subject[PATCH] ovl: only WARN_ON_ONCE() if dentry is NULL in ovl_encode_fh()
On Thu, Jul 28, 2022 at 4:57 PM Miklos Szeredi <miklos@szeredi.hu> wrote:
>
> On Thu, 28 Jul 2022 at 08:39, Jiachen Zhang
> <zhangjiachen.jaycee@bytedance.com> wrote:
> >
> > Some code paths cannot guarantee the inode have any dentry alias. So
> > WARN_ON() all !dentry may flood the kernel logs.
> >
> > For example, when an overlayfs inode is watched by inotifywait (1), and
> > someone is trying to read the /proc/$(pidof inotifywait)/fdinfo/INOTIFY_FD,
> > at that time if the dentry has been reclaimed by kernel (such as
> > echo 2 > /proc/sys/vm/drop_caches), there will be a WARN_ON(). The
> > printed call stack would be like:
> >
> > ? show_mark_fhandle+0xf0/0xf0
> > show_mark_fhandle+0x4a/0xf0
> > ? show_mark_fhandle+0xf0/0xf0
> > ? seq_vprintf+0x30/0x50
> > ? seq_printf+0x53/0x70
> > ? show_mark_fhandle+0xf0/0xf0
> > inotify_fdinfo+0x70/0x90
> > show_fdinfo.isra.4+0x53/0x70
> > seq_show+0x130/0x170
> > seq_read+0x153/0x440
> > vfs_read+0x94/0x150
> > ksys_read+0x5f/0xe0
> > do_syscall_64+0x59/0x1e0
> > entry_SYSCALL_64_after_hwframe+0x44/0xa9
> >
> > So let's replace WARN_ON() with WARN_ON_ONCE() to avoid kernel log
> > flooding.
>
> Better just drop the WARN_ON() completely in that case, since it's a
> normally occurring condition.
>
> Thanks,
> Miklos

OK. I will send the v2 patch later.

Thanks,
Jiachen

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