linux-kernel - Re: [PATCH v3] /dev/mem: Bail out upon SIGKILL.

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Message-ID: <20190826132916.GB12281@kroah.com>
Date:   Mon, 26 Aug 2019 15:29:16 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        syzbot <syzbot+8ab2d0f39fb79fe6ca40@...kaller.appspotmail.com>
Subject: Re: [PATCH v3] /dev/mem: Bail out upon SIGKILL.

On Mon, Aug 26, 2019 at 10:13:25PM +0900, Tetsuo Handa wrote:
> syzbot found that a thread can stall for minutes inside read_mem() or
> write_mem() after that thread was killed by SIGKILL [1]. Reading from
> iomem areas of /dev/mem can be slow, depending on the hardware.
> While reading 2GB at one read() is legal, delaying termination of killed
> thread for minutes is bad. Thus, allow reading/writing /dev/mem and
> /dev/kmem to be preemptible and killable.
> 
>   [ 1335.912419][T20577] read_mem: sz=4096 count=2134565632
>   [ 1335.943194][T20577] read_mem: sz=4096 count=2134561536
>   [ 1335.978280][T20577] read_mem: sz=4096 count=2134557440
>   [ 1336.011147][T20577] read_mem: sz=4096 count=2134553344
>   [ 1336.041897][T20577] read_mem: sz=4096 count=2134549248
> 
> Theoretically, reading/writing /dev/mem and /dev/kmem can become
> "interruptible". But this patch chose "killable". Future patch will make
> them "interruptible" so that we can revert to "killable" if some program
> regressed.
> 
> [1] https://syzkaller.appspot.com/bug?id=a0e3436829698d5824231251fad9d8e998f94f5e
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Reported-by: syzbot <syzbot+8ab2d0f39fb79fe6ca40@...kaller.appspotmail.com>
> ---
>  drivers/char/mem.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)

What changed from previous versions?

That goes below the --- line at the very least.

thanks,

greg k-h