linux-kernel - Re: [PATCH 2/3] fd/locks: allow get the lock owner by F_OFD

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Date:   Tue, 20 Jun 2023 06:51:41 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     Stas Sergeev <stsp2@...dex.ru>, linux-kernel@...r.kernel.org
Cc:     Chuck Lever <chuck.lever@...cle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 2/3] fd/locks: allow get the lock owner by F_OFD_GETLK

On Tue, 2023-06-20 at 14:55 +0500, Stas Sergeev wrote:
> Currently F_OFD_GETLK sets the pid of the lock owner to -1.
> Remove such behavior to allow getting the proper owner's pid.
> This may be helpful when you want to send some message (like SIGKILL)
> to the offending locker.
> 
> Signed-off-by: Stas Sergeev <stsp2@...dex.ru>
> 
> CC: Jeff Layton <jlayton@...nel.org>
> CC: Chuck Lever <chuck.lever@...cle.com>
> CC: Alexander Viro <viro@...iv.linux.org.uk>
> CC: Christian Brauner <brauner@...nel.org>
> CC: linux-fsdevel@...r.kernel.org
> CC: linux-kernel@...r.kernel.org
> 
> ---
>  fs/locks.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/fs/locks.c b/fs/locks.c
> index 210766007e63..ee265e166542 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -2158,8 +2158,6 @@ static pid_t locks_translate_pid(struct file_lock *fl, struct pid_namespace *ns)
>  	pid_t vnr;
>  	struct pid *pid;
>  
> -	if (IS_OFDLCK(fl))
> -		return -1;
>  	if (IS_REMOTELCK(fl))
>  		return fl->fl_pid;
>  	/*

NACK on this one.

OFD locks are not owned by processes. They are owned by the file
description (hence the name). Because of this, returning a pid here is
wrong.

This precedent comes from BSD, where flock() and POSIX locks can
conflict. BSD returns -1 for the pid if you call F_GETLK on a file
locked with flock(). Since OFD locks have similar ownership semantics to
flock() locks, we use the same convention here.

Cheers, 
-- 
Jeff Layton <jlayton@...nel.org>