linux-kernel - Re: [patch 2/5] signalfd v2

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Message-ID: <Pine.LNX.4.64.0703081459350.4882@alien.or.mcafeemobile.com>
Date:	Thu, 8 Mar 2007 15:05:20 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Oleg Nesterov <oleg@...sign.ru>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Avi Kivity <avi@...o.co.il>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [patch 2/5] signalfd v2 - signalfd core ...

On Fri, 9 Mar 2007, Oleg Nesterov wrote:

> > Logic is, if it's not an RT signal, queue only one, otherwise multiple.
> > The bit on the ->pending mask is clealer only when the queue slot becomes empty.
> 
> Yes, I see what the code does, but I don't undestand why. For example, SIGCHLD was
> delivered to the process _and_ handled several times, then sys_signalfd_dequeue()
> comes and finds only one siginfo. Isn't this strange?

That's the same logic the kernel folows for non-RT signals. 


> > The two trasports can rely on different masks. The signalfd_notify() does 
> > not even go in signalfd_deliver() if no signalfds are attached to the 
> > sighand.
> 
> Sorry, I don't understand. The masks are different, yes, but ->sighand is the
> same? How this can make any difference for "if no signalfds are attached" ?

The list_empty() che would not make you fall inside signalfd_deliver(), 
hence the fast path really lives up to its name ;)


> Also. A malicious user can eat all memory, signalfd_deliver()->kmem_cache_alloc()
> doesn't check any limits.

I'll make that use the std dequeu_signal, so everything is handled in there.



- Davide


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