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

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Message-Id: <1182554371.24740.87.camel@localhost.localdomain>
Date:	Sat, 23 Jun 2007 09:19:31 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Oleg Nesterov <oleg@...sign.ru>,
	Davide Libenzi <davidel@...ilserver.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 Sat, 2007-06-23 at 09:16 +1000, Benjamin Herrenschmidt wrote:
> On Fri, 2007-06-22 at 15:47 -0700, Linus Torvalds wrote:
> > Quite frankly, it strikes me that if we want to do this, then we shouldn't 
> > save the _process_ information at all, we should save the "sighand" 
> > instead.
> > 
> > So either we save the process info, or we save the sighand, but saving the 
> > "group_leader" seems totally bogus. Especially as the group leader can 
> > change (by execve()).
> > 
> > One thing that strikes me as I look at that function is that the whole 
> > signalfd thing doesn't seem to do any reference counting. Ie it looks 
> > totally buggy wrt passing the resulting fd off to somebody else, and then 
> > exiting in the original process.
> > 
> > What did I miss? 
> 
> Probably nothing... doesn't look good. What are the lifetime rules of a
> struct sighand tho ?

Ah got it, signalfd_detach() in include/linux/signalfd.h from
exit_signal plus some rcu bits in signalfd lock/unlock.

Ben.


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