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 15:57:23 +0500
From:   stsp <stsp2@...dex.ru>
To:     Jeff Layton <jlayton@...nel.org>, 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

Hello,

20.06.2023 15:51, Jeff Layton пишет:
> 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.

But fd is owned by a process.
PID has a meaning, you can send SIGKILL
to the returned PID, and the lock is clear.
Was there any reason to hide the PID at
a first place?


> 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.
OK if you insist I can drop this one and
search the PID by some other means.
Just a bit unsure what makes it so important
to overwrite the potentially useful info
with -1.

So in case you insist on that, then should
I send a v2 or can you just drop the patch
yourself?