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

[Richard Weinberger]

On Fri, May 1, 2015 at 8:37 PM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> 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
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