From: Matthew Wilcox <willy@infradead.org>
To: Jeff Layton <jlayton@kernel.org>
Cc: Amir Goldstein <amir73il@gmail.com>,
Sargun Dhillon <sargun@sargun.me>,
Miklos Szeredi <miklos@szeredi.hu>,
Vivek Goyal <vgoyal@redhat.com>,
overlayfs <linux-unionfs@vger.kernel.org>,
Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
NeilBrown <neilb@suse.com>, Jan Kara <jack@suse.cz>
Subject: Re: [PATCH v3] errseq: split the ERRSEQ_SEEN flag into two new flags
Date: Sat, 19 Dec 2020 06:13:31 +0000 [thread overview]
Message-ID: <20201219061331.GQ15600@casper.infradead.org> (raw)
In-Reply-To: <20201217150037.468787-1-jlayton@kernel.org>
On Thu, Dec 17, 2020 at 10:00:37AM -0500, Jeff Layton wrote:
> Overlayfs's volatile mounts want to be able to sample an error for their
> own purposes, without preventing a later opener from potentially seeing
> the error.
umm ... can't they just copy the errseq_t they're interested in, followed
by calling errseq_check() later?
actually, isn't errseq_check() buggy in the face of multiple
watchers? consider this:
worker.es starts at 0
t2.es = errseq_sample(&worker.es)
errseq_set(&worker.es, -EIO)
t1.es = errseq_sample(&worker.es)
t2.err = errseq_check_and_advance(&es, t2.es)
** this sets ERRSEQ_SEEN **
t1.err = errseq_check(&worker.es, t1.es)
** reports an error, even though the only change is that
ERRSEQ_SEEN moved **.
i think errseq_check() should be:
if (likely(cur | ERRSEQ_SEEN) == (since | ERRSEQ_SEEN))
return 0;
i'm not yet convinced other changes are needed to errseq. but i am
having great trouble understanding exactly what overlayfs is trying to do.
next prev parent reply other threads:[~2020-12-19 6:14 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-17 15:00 [PATCH v3] errseq: split the ERRSEQ_SEEN flag into two new flags Jeff Layton
2020-12-17 20:35 ` Sargun Dhillon
2020-12-17 21:18 ` Jeff Layton
2020-12-18 23:44 ` Sargun Dhillon
2020-12-19 1:03 ` Jeff Layton
2020-12-19 9:09 ` Amir Goldstein
2020-12-19 6:13 ` Matthew Wilcox [this message]
2020-12-19 12:53 ` Jeff Layton
2020-12-19 13:25 ` Jeff Layton
2020-12-19 15:33 ` Matthew Wilcox
2020-12-19 15:49 ` Jeff Layton
2020-12-19 16:53 ` Matthew Wilcox
2020-12-21 15:14 ` Vivek Goyal
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