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SubjectRe: RT signal queue overflow (Was: Q: SEGSEGV && uc_mcontext->ip (Was: Signal delivery order))


On Wed, 18 Mar 2009, Gábor 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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