From: Jeff Layton <jlayton@kernel.org>
To: stsp <stsp2@yandex.ru>, linux-kernel@vger.kernel.org
Cc: Chuck Lever <chuck.lever@oracle.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Christian Brauner <brauner@kernel.org>,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 2/3] fd/locks: allow get the lock owner by F_OFD_GETLK
Date: Tue, 20 Jun 2023 09:58:39 -0400 [thread overview]
Message-ID: <e8c8c7d8bf871a0282f3e629d017c09ed38e2c5e.camel@kernel.org> (raw)
In-Reply-To: <ddb48e05-ab26-ae5d-86d5-01e47f0f0cd2@yandex.ru>
On Tue, 2023-06-20 at 18:39 +0500, stsp wrote:
> 20.06.2023 18:19, Jeff Layton пишет:
> > The bottom line is that these locks are specifically not owned by a
> > process, so returning the l_pid field is unreliable (at best). There is
> > no guarantee that the pid returned will still represent the task that
> > set the lock.
>
> Though it will, for sure, represent the
> task that _owns_ the lock.
>
> > You may want to review this article. They're called "File-private" locks
> > here, but the name was later changed to "Open file description" (OFD)
> > locks:
> >
> > https://lwn.net/Articles/586904/
> >
> > The rationale for why -1 is reported is noted there.
> Well, they point to fork() and SCM_RIGHTS.
> Yes, these 2 beasts can make the same lock
> owned by more than one process.
> Yet l_pid returned, is going to be always valid:
> it will still represent one of the valid owners.
No, it won't. The l_pid field is populated from the file_lock->fl_pid.
That field is set when the lock is set, and never updated. So it's quite
possible for F_GETLK to return the pid of a process that no longer
exists.
In principle, we could try to address that by changing how we track lock
ownership, but that's a fairly major overhaul, and I'm not clear on any
use-cases where that matters.
> So my call is to be brave and just re-consider
> the conclusion of that article, made 10 years
> ago! :)
>
I think my foot has too many bullet wounds for that sort of bravery.
> Of course if returning just 1 of possibly multiple
> owners is a problem, then oh well, I'll drop
> this patch.
--
Jeff Layton <jlayton@kernel.org>
next prev parent reply other threads:[~2023-06-20 13:58 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-20 9:55 [PATCH 0/3] RFC: F_OFD_GETLK should provide more info Stas Sergeev
2023-06-20 9:55 ` [PATCH 1/3] fs/locks: F_UNLCK extension for F_OFD_GETLK Stas Sergeev
2023-06-20 10:46 ` Jeff Layton
2023-06-20 11:00 ` stsp
2023-06-20 11:15 ` Jeff Layton
2023-06-21 15:24 ` stsp
2023-06-20 9:55 ` [PATCH 2/3] fd/locks: allow get the lock owner by F_OFD_GETLK Stas Sergeev
2023-06-20 10:51 ` Jeff Layton
2023-06-20 10:57 ` stsp
2023-06-20 11:12 ` Jeff Layton
2023-06-20 11:45 ` stsp
2023-06-20 12:02 ` Jeff Layton
2023-06-20 12:34 ` stsp
2023-06-20 13:19 ` Jeff Layton
2023-06-20 13:39 ` stsp
2023-06-20 13:46 ` Matthew Wilcox
2023-06-20 13:47 ` stsp
2023-06-20 14:36 ` Matthew Wilcox
2023-06-20 15:45 ` stsp
2023-06-20 17:05 ` Matthew Wilcox
2023-06-21 2:54 ` stsp
2023-06-23 13:10 ` David Laight
2023-06-20 13:58 ` Jeff Layton [this message]
2023-06-21 6:57 ` stsp
2023-06-21 10:35 ` Jeff Layton
2023-06-21 10:42 ` stsp
2023-06-21 11:05 ` Jeff Layton
2023-06-21 11:22 ` stsp
2023-06-21 11:26 ` stsp
2023-06-23 15:25 ` Christian Brauner
2023-06-23 17:18 ` stsp
2023-06-27 16:00 ` Jeff Layton
2023-06-27 16:20 ` stsp
2023-06-20 9:55 ` [PATCH 3/3] selftests: add OFD lock tests Stas Sergeev
2023-06-20 11:06 ` Jeff Layton
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