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

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Date:   Mon, 8 Feb 2021 10:39:49 +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 Wed, Feb 03, 2021 at 03:41:56PM +0300, Pavel Tikhomirov wrote:
> Currently there is no way to differentiate the file with alive owner
> from the file with dead owner but pid of the owner reused. That's why
> CRIU can't actually know if it needs to restore file owner or not,
> because if it restores owner but actual owner was dead, this can
> introduce unexpected signals to the "false"-owner (which reused the
> pid).
> 
> Let's change the api, so that F_GETOWN(EX) returns 0 in case actual
> owner is dead already.
> 
> Cc: Jeff Layton <jlayton@...nel.org>
> Cc: "J. Bruce Fields" <bfields@...ldses.org>
> Cc: Alexander Viro <viro@...iv.linux.org.uk>
> Cc: linux-fsdevel@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Cc: Cyrill Gorcunov <gorcunov@...il.com>
> Cc: Andrei Vagin <avagin@...il.com>
> Signed-off-by: Pavel Tikhomirov <ptikhomirov@...tuozzo.com>

I can't imagine a scenario where we could break some backward
compatibility with this change, so

Reviewed-by: Cyrill Gorcunov <gorcunov@...il.com>