linux-kernel - Re: [PATCH] ext4: call fallocate may cause process to hang when using fast commit

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Date:   Wed, 22 Dec 2021 18:44:33 -0800
From:   harshad shirwadkar <harshadshirwadkar@...il.com>
To:     Xin Yin <yinxin.x@...edance.com>
Cc:     "Theodore Y. Ts'o" <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ext4: call fallocate may cause process to hang when using
 fast commit

Once the patch series "ext4 fast commit API cleanup" gets merged in
(https://patchwork.ozlabs.org/project/linux-ext4/list/?series=277672),
this patch won't be required anymore. So, I'll undo my review in favor
of merging the API cleanup patch series first.

- Harshad

On Fri, Dec 17, 2021 at 12:17 PM harshad shirwadkar
<harshadshirwadkar@...il.com> wrote:
>
> Thanks for the patch Xin, it looks good to me. I think there are a few
> other places where we are not stopping the transaction before calling
> commit. I'm trying to find them out.
>
> Reviewed-by: Harshad Shirwadkar <harshadshirwadkar@...il.com>
>
> On Thu, Dec 16, 2021 at 12:04 AM Xin Yin <yinxin.x@...edance.com> wrote:
> >
> > If open a file with O_SYNC, and call fallocate with mode=0.when using
> > fast commit, will cause the process to hang.
> >
> > During the fast_commit procedure, it will wait for inode update done.
> > call ext4_fc_stop_update() before ext4_fc_commit() to mark inode
> > complete update.
> >
> > Signed-off-by: Xin Yin <yinxin.x@...edance.com>
> > ---
> >  fs/ext4/extents.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> > index 4108896d471b..92db33887b6c 100644
> > --- a/fs/ext4/extents.c
> > +++ b/fs/ext4/extents.c
> > @@ -4707,8 +4707,12 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
> >                 goto out;
> >
> >         if (file->f_flags & O_SYNC && EXT4_SB(inode->i_sb)->s_journal) {
> > +               ext4_fc_stop_update(inode);
> >                 ret = ext4_fc_commit(EXT4_SB(inode->i_sb)->s_journal,
> >                                         EXT4_I(inode)->i_sync_tid);
> > +               inode_unlock(inode);
> > +               trace_ext4_fallocate_exit(inode, offset, max_blocks, ret);
> > +               return ret;
> >         }
> >  out:
> >         inode_unlock(inode);
> > --
> > 2.20.1
> >