Date: Wed, 18 Mar 2009 07:52:23 -0700 (PDT)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: =?ISO-8859-15?Q?G=E1bor_Melis?= <mega@retes.hu>
cc: Roland McGrath <roland@redhat.com>, Oleg Nesterov <oleg@redhat.com>,
       Davide Libenzi <davidel@xmailserver.org>, Ingo Molnar <mingo@elte.hu>,
       Andrew Morton <akpm@linux-foundation.org>,
       Chris Friesen <cfriesen@nortel.com>, linux-kernel@vger.kernel.org
Subject: Re: RT signal queue overflow (Was: Q: SEGSEGV && uc_mcontext->ip
 (Was: Signal delivery order))
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On Wed, 18 Mar 2009, G?bor Melis wrote:
> 
> It was just a month or so ago when I finally made to change to use a 
> non-real-time signal for signalling stop-for-gc.

Ahh, and that is when you noticed the issue with SIGSEGV?

One thing you might try is to still use a non-real-time signal, but simply 
depend on the fact that signals are basically peeled off the signal 
bitmask in a signal number order (with the exception that fatal signals 
are handled specially).

IOW, on x86, just about the _only_ normal user-generated signal that can 
happen before SIGSEGV is SIGUSR1, because SIGSEGV is 11, and SIGUSR1 is 
10.

If you were to use SIGUSR2 (signal #12) you'd probably never see this.

Of course, there are other signals with numbers < 11, but they are 
generally meant for other synchronous traps (ie signals like 
SIGTRAP/AIGABRT/SIGFPE/SIGBUS), or for killing the process (signals
SIGHUP/SIGINT/SIGQUIT).

So maybe you'd be happy with just picking another signal? It's not a 
_pretty_ solution, but it should work across most kernel versions.

			Linus
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