From: Matthew Wilcox <willy@infradead.org>
To: Andreas Gruenbacher <agruenba@redhat.com>
Cc: linux-fsdevel@vger.kernel.org, cluster-devel@redhat.com,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Jan Kara <jack@suse.cz>
Subject: Re: [PATCH] [RFC] Trigger retry from fault vm operation
Date: Tue, 11 May 2021 15:11:00 +0100 [thread overview]
Message-ID: <YJqQdKmBHz6oEqD1@casper.infradead.org> (raw)
In-Reply-To: <20210511140113.1225981-1-agruenba@redhat.com>
On Tue, May 11, 2021 at 04:01:13PM +0200, Andreas Gruenbacher wrote:
> we have a locking problem in gfs2 that I don't have a proper solution for, so
> I'm looking for suggestions.
>
> What's happening is that a page fault triggers during a read or write
> operation, while we're holding a glock (the cluster-wide gfs2 inode
> lock), and the page fault requires another glock. We can recognize and
> handle the case when both glocks are the same, but when the page fault requires
> another glock, there is a chance that taking that other glock would deadlock.
So we're looking at something like one file on a gfs2 filesystem being
mmaped() and then doing read() or write() to another gfs2 file with the
mmaped address being the passed to read()/write()?
Have you looked at iov_iter_fault_in_readable() as a solution to
your locking order? That way, you bring the mmaped page in first
(see generic_perform_write()).
> When we realize that we may not be able to take the other glock in gfs2_fault,
> we need to communicate that to the read or write operation, which will then
> drop and re-acquire the "outer" glock and retry. However, there doesn't seem
> to be a good way to do that; we can only indicate that a page fault should fail
> by returning VM_FAULT_SIGBUS or similar; that will then be mapped to -EFAULT.
> We'd need something like VM_FAULT_RESTART that can be mapped to -EBUSY so that
> we can tell the retry case apart from genuine -EFAULT errors.
We do have VM_FAULT_RETRY ... does that retry at the wrong level?
next prev parent reply other threads:[~2021-05-11 14:11 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-11 14:01 [PATCH] [RFC] Trigger retry from fault vm operation Andreas Gruenbacher
2021-05-11 14:11 ` Matthew Wilcox [this message]
2021-05-11 14:59 ` Andreas Gruenbacher
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YJqQdKmBHz6oEqD1@casper.infradead.org \
--to=willy@infradead.org \
--cc=agruenba@redhat.com \
--cc=cluster-devel@redhat.com \
--cc=jack@suse.cz \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).