> One difference in 2.4.x and 2.6.x is the signal blocking
> wrt blocked signals that are _forced_ (ie anything that
> is thread-synchronous, like a SIGSEGV/SIGTRAP/SIGBUS that
> happens as a result of a fault):
>
> - in 2.4.x they will just punch through the block
> - in 2.6.x they will refuse to punch through a blocked
> signal, but since they can't be delivered they will
> cause the process to be killed.
...
> and in 2.4.x this will cause infinte SIGSEGV's (well,
> they'll be caught by the stack size eventually, but you
> see the problem: do a "strace" to see what's going on).
> In 2.6.x the second SIGSEGV will just kill the program
> immediately.
How about making the process sleep in a killable state?
This is as if the blocking was obeyed, but doesn't
burn CPU time. Only a debugger should be able to
tell the difference.
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On Wednesday 26 November 2003 22:53, Albert Cahalan wrote:
[2.4 vs. 2.6 wrt. thread synchronous signals]
> How about making the process sleep in a killable state?
>
> This is as if the blocking was obeyed, but doesn't
> burn CPU time. Only a debugger should be able to
> tell the difference.
This has 2 problems:
1) Servers and PID files or servers and simple monitoring software.
2) Processes spawned from init, which will not respawn.
Regards
Ingo Oeser
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On Thu, 2003-11-27 at 04:11, Ingo Oeser wrote:
> On Wednesday 26 November 2003 22:53, Albert Cahalan wrote:
> [2.4 vs. 2.6 wrt. thread synchronous signals]
> > How about making the process sleep in a killable state?
> >
> > This is as if the blocking was obeyed, but doesn't
> > burn CPU time. Only a debugger should be able to
> > tell the difference.
>
> This has 2 problems:
>
> 1) Servers and PID files or servers and simple monitoring software.
> 2) Processes spawned from init, which will not respawn.
It has benefits:
1. Continuous respawning is no good.
2. If the processes sleeps, you can attach a debugger.
The obviously correct behavior is to go back into
user space, likely to take the signal again. The only
thing wrong with this is that it eats CPU time.
So _pretend_ to do that. Have the process sleep,
ideally with an "R" state as seen in /proc, and maybe
even go back to the crazy loop if someone attaches a
debugger.
The crazy loop is most correct though. It's what the
user asked for. It perfectly handles the case of a
repeating SIGFPE (blocked) followed by some other
thread unmapping a page of instructions or data that
turns the SIGFPE into a SIGSEGV.
On Thu, 27 November 2003 10:45:39 -0500, Albert Cahalan wrote:
>
> It has benefits:
>
> 1. Continuous respawning is no good.
But trivial to notice. :)
> 2. If the processes sleeps, you can attach a debugger.
If aunt Tilly has a core dump, her son can extract it and send it to
some developer. No need for you to drive over to aunt Tilly.
> The obviously correct behavior is to go back into
> user space, likely to take the signal again. The only
> thing wrong with this is that it eats CPU time.
> So _pretend_ to do that. Have the process sleep,
> ideally with an "R" state as seen in /proc, and maybe
> even go back to the crazy loop if someone attaches a
> debugger.
>
> The crazy loop is most correct though. It's what the
> user asked for. It perfectly handles the case of a
> repeating SIGFPE (blocked) followed by some other
> thread unmapping a page of instructions or data that
> turns the SIGFPE into a SIGSEGV.
"It just what you asked for, but not what you wanted."
I am a firm non-believer in the trust-the-programmer paradigm. How
many people actually intend to do NULL-pointer dereferences, etc? To
make this possible "if you really really want to" is ok, but at least
make the bad behaviour hard to trigger by accident.
What Linux did in 2.5.7x is not exacly what I would have done, but it
makes it hard to do the Wrong Thing (tm) by accident, while allowing
it for those who really want it. Good enough for most users.
J?rn
--
Those who come seeking peace without a treaty are plotting.
-- Sun Tzu