Re: [PATCH v2] ovl: drop WARN_ON() dentry is NULL in ovl_encode_fh()

From: Miklos Szeredi
Date: Thu Jul 28 2022 - 09:06:11 EST


On Thu, 28 Jul 2022 at 13:49, Jiachen Zhang
<zhangjiachen.jaycee@xxxxxxxxxxxxx> 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 drop WARN_ON() to avoid kernel log flooding.


Applied, thanks.

Miklos