From: Al Viro <viro@zeniv.linux.org.uk>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: Miklos Szeredi <mszeredi@redhat.com>,
linux-fsdevel@vger.kernel.org, NeilBrown <neil@brown.name>
Subject: Re: [PATCH] fuse: prevent exchange/revalidate races
Date: Wed, 17 Sep 2025 18:45:58 +0100 [thread overview]
Message-ID: <20250917174558.GA1196114@ZenIV> (raw)
In-Reply-To: <20250917174350.GW39973@ZenIV>
On Wed, Sep 17, 2025 at 06:43:50PM +0100, Al Viro wrote:
> On Wed, Sep 17, 2025 at 07:27:25PM +0200, Miklos Szeredi wrote:
> > On Wed, 17 Sept 2025 at 18:41, Al Viro <viro@zeniv.linux.org.uk> wrote:
> > >
> > > On Wed, Sep 17, 2025 at 05:42:18PM +0200, Miklos Szeredi wrote:
> > > > > ... and if the call of ->d_revalidate() had been with parent locked, you've
> > > > > just got a deadlock in that case.
> > > >
> > > > Why?
> > >
> > > Because the locking order on directories is "ancestors first"; you are trying
> > > to grab an inode that is also a directory and might be anywhere in the tree
> > > by that point - that's precisely what you are trying to check, isn't it?
> >
> > But if parent is locked, it must not have been renamed, hence
> > parent-child relationship holds.
>
> Not if parent is held shared.
Note that lookup will reparent a subdirectory just fine - exclusive lock on
that directory's parent would make it fail, but shared one is not a problem.
next prev parent reply other threads:[~2025-09-17 17:46 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-09-17 15:30 [PATCH] fuse: prevent exchange/revalidate races Miklos Szeredi
2025-09-17 15:36 ` Al Viro
2025-09-17 15:42 ` Miklos Szeredi
2025-09-17 16:41 ` Al Viro
2025-09-17 17:27 ` Miklos Szeredi
2025-09-17 17:43 ` Al Viro
2025-09-17 17:45 ` Al Viro [this message]
2025-09-18 1:43 ` NeilBrown
2025-09-18 10:02 ` Miklos Szeredi
2025-09-19 8:20 ` Miklos Szeredi
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=20250917174558.GA1196114@ZenIV \
--to=viro@zeniv.linux.org.uk \
--cc=linux-fsdevel@vger.kernel.org \
--cc=miklos@szeredi.hu \
--cc=mszeredi@redhat.com \
--cc=neil@brown.name \
/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).