linux-kernel - Re: [PATCH 5.1 038/371] signal/cifs: Fix cifs_put_tcp_session to call send_sig instead of force

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Message-ID: <CAH2r5msEhN2SJ+iNGPSqGJHEj4jswQK2xbV9S5xQ51E+wOcjUw@mail.gmail.com>
Date:   Wed, 24 Jul 2019 15:49:54 -0500
From:   Steve French <smfrench@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Stable <stable@...r.kernel.org>,
        Namjae Jeon <namjae.jeon@...sung.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 5.1 038/371] signal/cifs: Fix cifs_put_tcp_session to call
 send_sig instead of force_sig

Note that this patch causes a regression (removing cifs module fails,
due to unmount leaking a thread with this change).

We are testing a workaround to cifs.ko which would be needed if this
patch were to be backported.

On Wed, Jul 24, 2019 at 2:46 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> [ Upstream commit 72abe3bcf0911d69b46c1e8bdb5612675e0ac42c ]
>
> The locking in force_sig_info is not prepared to deal with a task that
> exits or execs (as sighand may change).  The is not a locking problem
> in force_sig as force_sig is only built to handle synchronous
> exceptions.
>
> Further the function force_sig_info changes the signal state if the
> signal is ignored, or blocked or if SIGNAL_UNKILLABLE will prevent the
> delivery of the signal.  The signal SIGKILL can not be ignored and can
> not be blocked and SIGNAL_UNKILLABLE won't prevent it from being
> delivered.
>
> So using force_sig rather than send_sig for SIGKILL is confusing
> and pointless.
>
> Because it won't impact the sending of the signal and and because
> using force_sig is wrong, replace force_sig with send_sig.
>
> Cc: Namjae Jeon <namjae.jeon@...sung.com>
> Cc: Jeff Layton <jlayton@...marydata.com>
> Cc: Steve French <smfrench@...il.com>
> Fixes: a5c3e1c725af ("Revert "cifs: No need to send SIGKILL to demux_thread during umount"")
> Fixes: e7ddee9037e7 ("cifs: disable sharing session and tcon and add new TCP sharing code")
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  fs/cifs/connect.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
> index e9507fba0b36..10851bb74253 100644
> --- a/fs/cifs/connect.c
> +++ b/fs/cifs/connect.c
> @@ -2625,7 +2625,7 @@ cifs_put_tcp_session(struct TCP_Server_Info *server, int from_reconnect)
>
>         task = xchg(&server->tsk, NULL);
>         if (task)
> -               force_sig(SIGKILL, task);
> +               send_sig(SIGKILL, task, 1);
>  }
>
>  static struct TCP_Server_Info *
> --
> 2.20.1
>
>
>


-- 
Thanks,

Steve