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

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Message-ID: <Pine.LNX.4.64.0706221554420.3880@alien.or.mcafeemobile.com>
Date:	Fri, 22 Jun 2007 16:00:53 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Oleg Nesterov <oleg@...sign.ru>,
	Nicholas Miell <nmiell@...cast.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Fix signalfd interaction with thread-private signals

On Fri, 22 Jun 2007, 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?

We intercept the sighand going out of business, and we do not access it 
anymore after that (by the mean of signalfd_lock() returning zero).
I'd be OK with Oleg patch, although I really prefer signalfd being more 
flexible (that is, with sync signals disabled in signalfd, and with Ben's 
patch reverted). Unless clear point of breakage are shown with such 
approach.



- Davide


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