From: Jeff Layton <jlayton@kernel.org>
To: Vivek Goyal <vgoyal@redhat.com>, Matthew Wilcox <willy@infradead.org>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-unionfs@vger.kernel.org, amir73il@gmail.com,
sargun@sargun.me, miklos@szeredi.hu, jack@suse.cz,
neilb@suse.com, viro@zeniv.linux.org.uk, hch@lst.de
Subject: Re: [PATCH 3/3] overlayfs: Report writeback errors on upper
Date: Wed, 23 Dec 2020 07:53:43 -0500 [thread overview]
Message-ID: <dbc580cf9346aca06a3383533a09a794ca68917c.camel@kernel.org> (raw)
In-Reply-To: <20201222175518.GD3248@redhat.com>
On Tue, 2020-12-22 at 12:55 -0500, Vivek Goyal wrote:
> On Tue, Dec 22, 2020 at 05:46:37PM +0000, Matthew Wilcox wrote:
> > On Tue, Dec 22, 2020 at 11:29:25AM -0500, Vivek Goyal wrote:
> > > On Tue, Dec 22, 2020 at 04:20:27PM +0000, Matthew Wilcox wrote:
> > > > On Mon, Dec 21, 2020 at 02:50:55PM -0500, Vivek Goyal wrote:
> > > > > +static int ovl_errseq_check_advance(struct super_block *sb, struct file *file)
> > > > > +{
> > > > > + struct ovl_fs *ofs = sb->s_fs_info;
> > > > > + struct super_block *upper_sb;
> > > > > + int ret;
> > > > > +
> > > > > + if (!ovl_upper_mnt(ofs))
> > > > > + return 0;
> > > > > +
> > > > > + upper_sb = ovl_upper_mnt(ofs)->mnt_sb;
> > > > > +
> > > > > + if (!errseq_check(&upper_sb->s_wb_err, file->f_sb_err))
> > > > > + return 0;
> > > > > +
> > > > > + /* Something changed, must use slow path */
> > > > > + spin_lock(&file->f_lock);
> > > > > + ret = errseq_check_and_advance(&upper_sb->s_wb_err, &file->f_sb_err);
> > > > > + spin_unlock(&file->f_lock);
> > > >
> > > > Why are you microoptimising syncfs()? Are there really applications which
> > > > call syncfs() in a massively parallel manner on the same file descriptor?
> > >
> > > This is atleast theoritical race. I am not aware which application can
> > > trigger this race. So to me it makes sense to fix the race.
> > >
> > > Jeff Layton also posted a fix for syncfs().
> > >
> > > https://lore.kernel.org/linux-fsdevel/20201219134804.20034-1-jlayton@kernel.org/
> > >
> > > To me it makes sense to fix the race irrespective of the fact if somebody
> > > hit it or not. People end up copying code in other parts of kernel and
> > > and they will atleast copy race free code.
> >
> > Let me try again. "Why are you trying to avoid taking the spinlock?"
>
> Aha.., sorry, I misunderstood your question. I don't have a good answer.
> I just copied the code from Jeff Layton's patch.
>
> Agreed that cost of taking spin lock will not be significant until
> syncfs() is called at high frequency. Having said that, most of the
> time taking spin lock will not be needed, so avoiding it with
> a simple call to errseq_check() sounds reasonable too.
>
> I don't have any strong opinions here. I am fine with any of the
> implementation people like.
>
It is a micro-optimization, but we'll almost always be able to avoid
taking the lock altogether. Errors here should be very, very infrequent.
That said I don't have strong feelings on this either.
--
Jeff Layton <jlayton@kernel.org>
next prev parent reply other threads:[~2020-12-23 12:54 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-21 19:50 [RFC PATCH 0/3][v3] vfs, overlayfs: Fix syncfs() to return correct errors Vivek Goyal
2020-12-21 19:50 ` [PATCH 1/3] vfs: Do not ignore return code from s_op->sync_fs Vivek Goyal
2020-12-22 1:23 ` NeilBrown
2020-12-22 15:17 ` Vivek Goyal
2020-12-21 19:50 ` [PATCH 2/3] vfs: Add a super block operation to check for writeback errors Vivek Goyal
2020-12-22 16:19 ` Matthew Wilcox
2020-12-22 16:25 ` Vivek Goyal
2020-12-23 12:44 ` Jeff Layton
2020-12-23 12:48 ` Jeff Layton
2021-01-04 19:41 ` Vivek Goyal
2020-12-21 19:50 ` [PATCH 3/3] overlayfs: Report writeback errors on upper Vivek Goyal
2020-12-22 16:20 ` Matthew Wilcox
2020-12-22 16:29 ` Vivek Goyal
2020-12-22 17:46 ` Matthew Wilcox
2020-12-22 17:55 ` Vivek Goyal
2020-12-23 12:53 ` Jeff Layton [this message]
2020-12-23 18:20 ` Sargun Dhillon
2020-12-23 18:50 ` Matthew Wilcox
2020-12-23 19:29 ` Sargun Dhillon
2020-12-23 20:07 ` Matthew Wilcox
2020-12-23 20:21 ` Sargun Dhillon
2020-12-23 20:44 ` Matthew Wilcox
2020-12-24 9:32 ` Amir Goldstein
2020-12-24 10:12 ` Sargun Dhillon
2020-12-24 12:13 ` Matthew Wilcox
2020-12-25 6:50 ` Amir Goldstein
2020-12-28 13:25 ` Jeff Layton
2020-12-28 15:51 ` Amir Goldstein
2021-01-04 15:51 ` Vivek Goyal
2020-12-28 15:56 ` Matthew Wilcox
2020-12-28 17:26 ` Jeff Layton
2020-12-28 19:25 ` Sargun Dhillon
2020-12-28 19:37 ` Amir Goldstein
2020-12-28 20:48 ` Matthew Wilcox
2021-01-02 13:25 ` Jeff Layton
2021-01-04 16:59 ` Vivek Goyal
2021-01-04 15:14 ` Vivek Goyal
2021-01-04 15:22 ` Amir Goldstein
2021-01-04 15:40 ` Vivek Goyal
2021-01-04 21:42 ` Amir Goldstein
2021-01-04 22:44 ` Vivek Goyal
2021-01-05 7:11 ` Amir Goldstein
2021-01-05 16:26 ` Vivek Goyal
2021-01-05 16:57 ` Amir Goldstein
2020-12-23 19:00 ` Jeff Layton
2021-01-04 20:00 ` Vivek Goyal
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