linux-kernel - Re: [GIT PULL] VFIO fixes for v4.1-rc2

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Message-ID: <CAFLxGvwrH1OONi2stxuiqArDcijBmbtRBY+b6386Xmni9YUobg@mail.gmail.com>
Date:	Fri, 1 May 2015 23:09:04 +0200
From:	Richard Weinberger <richard.weinberger@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Alex Williamson <alex.williamson@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	kvm <kvm@...r.kernel.org>
Subject: Re: [GIT PULL] VFIO fixes for v4.1-rc2

...of course I meant t-> and not current->



On 5/1/15, Richard Weinberger <richard.weinberger@...il.com> wrote:
> On Fri, May 1, 2015 at 8:37 PM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
>> "flush_signals()" is only for kernel threads, where it's a hacky
>> alternative to actually handling them (since kernel threads never
>> rreturn to user space and cannot really "handle" a signal). But you're
>> doing it in the ->remove handler for the device, which can be called
>> by arbitrary system processes. This is not a kernel thread thing, as
>> far as I can see.
>>
>> If you cannot handle signals, you damn well shouldn't be using
>> "wait_event_interruptible_timeout()" to begin with. Get rid of the
>> "interruptible", since it apparently *isn't* interruptible.
>>
>> So I'm not pulling this.
>>
>> Now I'm worried that other drivers do insane things like this. I
>> wonder if we should add some sanity test to flush_signals() to make
>> sure that it can only ever get called from a kernel thread.
>
> Hmm, a quick grep exposes some questionable users.
> At least w1 looks fishy.
> drivers/w1/w1_family.c:w1_unregister_family
> drivers/w1/w1_int.c:__w1_remove_master_device
>
> What do you think about a WARN_ON like:
>
> diff --git a/kernel/signal.c b/kernel/signal.c
> index d51c5dd..b4079c3 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -427,6 +427,8 @@ void flush_signals(struct task_struct *t)
>  {
>         unsigned long flags;
>
> +       WARN_ON((current->flags & PF_KTHREAD) == 0);
> +
>         spin_lock_irqsave(&t->sighand->siglock, flags);
>         __flush_signals(t);
>         spin_unlock_irqrestore(&t->sighand->siglock, flags);
>
> --
> Thanks,
> //richard
>


-- 
Thanks,
//richard
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