linux-kernel - Re: [PATCH 1/3] signals: sigqueue_free: don't free sigqueue if it is queued

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Date:	Thu, 22 May 2008 18:41:35 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Austin Clements <amdragon+kernelbugzilla@....edu>,
	Ingo Molnar <mingo@...e.hu>, john stultz <johnstul@...ibm.com>,
	Michael Kerrisk <mtk.manpages@...glemail.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] signals: sigqueue_free: don't free sigqueue if it is queued

> So. Let's suppose that (say) SIGHUP is pending, and the posix timer
> sends SIGHUP too. In that case the new SIGHUP is added, and if the
> previous one was infoless the new one "hides" it: collect_signal()
> won't see 2 distinct signals, it will find only 1 signal and clear
> the bit in sigpending->signal.

That is correct behavior.  Signals < SIGRTMIN do not queue.  (POSIX says
it's implementation-defined whether they do, and in Linux they don't.)
When a signal does not queue, it's unspecified whether the the one that
is ever actually seen is the first one or the last one (or any in between),
so the siginfo_t details showing the second one in your example is fine.


Thanks,
Roland
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