linux-kernel - Re: [PATCH] ovl: skip overlayfs superblocks at global sync

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Message-ID: <CAJfpegvrRxYsN5L1GSWTCZgmBR4kf00YeD9JNx=fEd4fDKuOtg@mail.gmail.com>
Date:   Tue, 21 Apr 2020 11:36:39 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        overlayfs <linux-unionfs@...r.kernel.org>,
        Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>
Subject: Re: [PATCH] ovl: skip overlayfs superblocks at global sync

On Thu, Apr 9, 2020 at 10:29 AM Konstantin Khlebnikov
<khlebnikov@...dex-team.ru> wrote:
>
> Stacked filesystems like overlayfs has no own writeback, but they have to
> forward syncfs() requests to backend for keeping data integrity.
>
> During global sync() each overlayfs instance calls method ->sync_fs()
> for backend although it itself is in global list of superblocks too.
> As a result one syscall sync() could write one superblock several times
> and send multiple disk barriers.
>
> This patch adds flag SB_I_SKIP_SYNC into sb->sb_iflags to avoid that.
>
> Reported-by: Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>

Thanks, applied.

Miklos