linux-kernel - Re: Fix signalfd interaction with thread-private signals

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Message-ID: <20070619200818.GA122@tv-sign.ru>
Date:	Wed, 20 Jun 2007 00:08:18 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Nicholas Miell <nmiell@...cast.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Fix signalfd interaction with thread-private signals

On 06/19, Davide Libenzi wrote:
>
> On Tue, 19 Jun 2007, Oleg Nesterov wrote:
> 
> > On 06/19, Benjamin Herrenschmidt wrote:
> > >
> > > On Tue, 2007-06-19 at 13:14 +0400, Oleg Nesterov wrote:
> > > 
> > > > The commited "Fix signalfd interaction with thread-private signals"
> > > > (commit caec4e8dc85e0644ec24aeb36285e1ba02da58cc) doesn't implement
> > > > this.
> > > 
> > > Indeed, if you want what Davide described, you need to also change
> > > signalfd side. The patch I did merely prevents another thread from
> > > dequeuing somebody else private signals.
> > 
> > Yes I see, but why do we need this change? Yes, we can dequeue SIGSEGV
> > from another thread. Just don't do it if you have a handler for SIGSEGV?
> 
> I believe it can be confusing to have private signals dequeued from 
> another thread. The kernel expect those to be dequeued by the target 
> thread.

Well, I think the kernel doesn't make any assumptions on that. It can't
guarantee the signal will be actually dequeued, to begin with.

(That said, I probably missed something, in that case I'd like to be
 educated. This is the real reason why I am making the noise :)

Oleg.

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