linux-kernel - Re: signalfd API issues (was Re: [PATCH/RFC] signal races/bugs, losing TIF

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Date:	Thu, 07 Jun 2007 13:29:23 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Jeff Dike <jdike@...toit.com>
Cc:	Paul Mackerras <paulus@...ba.org>,
	Nicholas Miell <nmiell@...cast.net>,
	Davide Libenzi <davidel@...ilserver.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: signalfd API issues (was Re: [PATCH/RFC] signal races/bugs,
	losing TIF_SIGPENDING and other woes)

On Wed, 2007-06-06 at 22:20 -0400, Jeff Dike wrote:
> On Thu, Jun 07, 2007 at 08:43:42AM +1000, Paul Mackerras wrote:
> > What Ben was talking about was stealing a synchronous SEGV from a task
> > without stopping it, and as Ben says that makes no sense.
> > Intercepting a signal and stopping the task is reasonable, and that is
> > what ptrace does, and I assume also UML.
> 
> It is, but I can also see UML stealing the SEGV from the child.  The
> UML skas does this - a ptrace extension, PTRACE_FAULTINFO, is used to
> extract page fault information from the child, and other pieces of the
> patch are used to fix the fault without the child continuing until
> it's fixed.  So, in this case, the child never sees the SEGV.

But you use ptrace and don't steal signals with dequeue_signal() on a
live other task, which is ok.

Ben.


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