Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220728114915.91021-1-zhangjiachen.jaycee@bytedance.com>
In-Reply-To: <20220728114915.91021-1-zhangjiachen.jaycee@bytedance.com>
From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Thu, 28 Jul 2022 15:05:50 +0200
Message-ID: <CAJfpegtxUrytqTFjVG0J03ZmEzzpFr8Ra1KP8HiZNPzTtgY3kw@mail.gmail.com>
Subject: Re: [PATCH v2] ovl: drop WARN_ON() dentry is NULL in ovl_encode_fh()
To:     Jiachen Zhang <zhangjiachen.jaycee@bytedance.com>
Cc:     overlayfs <linux-unionfs@vger.kernel.org>,
        linux-kernel@vger.kernel.org, songmuchun@bytedance.com,
        Hongbo Yin <yinhongbo@bytedance.com>,
        Tianci Zhang <zhangtianci.1997@bytedance.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, 28 Jul 2022 at 13:49, 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 drop WARN_ON() to avoid kernel log flooding.


Applied, thanks.

Miklos