linux-kernel - Re: [PATCH] fcntl: make F_GETOWN(EX) return 0 on dead owner task

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Date:   Thu, 4 Feb 2021 01:17:26 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
Cc:     Jeff Layton <jlayton@...chiereds.net>,
        Jeff Layton <jlayton@...nel.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andrei Vagin <avagin@...il.com>
Subject: Re: [PATCH] fcntl: make F_GETOWN(EX) return 0 on dead owner task

On Thu, Feb 04, 2021 at 12:35:42AM +0300, Pavel Tikhomirov wrote:
> 
> AFAICS if pid is held only by 1) fowner refcount and by 2) single process
> (without threads, group and session for simplicity), on process exit we go
> through:
> 
> do_exit
>   exit_notify
>     release_task
>       __exit_signal
>         __unhash_process
>           detach_pid
>             __change_pid
>               free_pid
>                 idr_remove
> 
> So pid is removed from idr, and after that alloc_pid can reuse pid numbers
> even if old pid structure is still alive and is still held by fowner.
...
> Hope this answers your question, Thanks!

Yeah, indeed, thanks! So the change is sane still I'm
a bit worried about backward compatibility, gimme some
time I'll try to refresh my memory first, in a couple
of days or weekend (though here are a number of experienced
developers CC'ed maybe they reply even faster).