* Stas Sergeev <[email protected]> [2016-03-01 00:29:03 +0300]:
> The following patches make it possible to use swapcontext()
> in a sighandler that works on sigaltstack.
i don't think that's possible, the (obsolete) userspace
*context functions cannot operate on kernel provided
ucontext_t structs, so they are not usable in signal
handlers.
at least not on most target archs.
so i don't understand how the tests can work portably.
> The approach is inspired by Andy Lutomirski's suggestion that
> sigaltstack should disarm itself after saving into uc_stack:
> https://lkml.org/lkml/2016/2/1/594
>
> I add the SS_AUTODISARM flag that does exactly that.
> On sighandler exit, the sigaltstack is restored from uc_stack.
> Another possible name could be SS_ONESHOT, but, since it gets
> always re-enabled, I choose SS_AUTODISARM.
>
> [PATCH 1/2] sigaltstack: implement SS_AUTODISARM flag
> This patch implements SS_AUTODISARM flag
> [PATCH 2/2] selftests: Add test for sigaltstack(SS_AUTODISARM)
> This patch adds the selftest code for new functionality
>
> CC: [email protected]
> CC: [email protected]
> CC: Andy Lutomirski <[email protected]>
> CC: Oleg Nesterov <[email protected]>
> CC: Shuah Khan <[email protected]>
>
> Diffstat:
> include/linux/sched.h | 8 +
> include/linux/signal.h | 4
> include/uapi/linux/signal.h | 3
> kernel/fork.c | 2
> kernel/signal.c | 23 ++--
> tools/testing/selftests/Makefile | 1
> tools/testing/selftests/sigaltstack/Makefile | 8 +
> tools/testing/selftests/sigaltstack/sas.c | 151 +++++++++++++++++++++++++++
> 8 files changed, 187 insertions(+), 13 deletions(-)
>
> --
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06.03.2016 23:02, Szabolcs Nagy пишет:
> * Stas Sergeev <[email protected]> [2016-03-01 00:29:03 +0300]:
>> The following patches make it possible to use swapcontext()
>> in a sighandler that works on sigaltstack.
> i don't think that's possible, the (obsolete) userspace
> *context functions cannot operate on kernel provided
> ucontext_t structs,
It doesn't have to.
It does the normal getcontext()/swapcontext() sequences,
as if it would be switching from any casual code place.
Kernel-provided context structs are completely irrelevant.
For more details please see the test-case I posted in that patch series.
It shows what can be done and how.
> so they are not usable in signal
> handlers.
Please note the fact that swapcontext() also replaces the
signal mask as part of the context switching. This is a very
strong hint that it was intended to work with signal handlers.
And in fact it perfectly does.
What I want is only to make it friendly to sigaltstack.
I am not making it friendly to signal handlers in general,
because it already is.
> at least not on most target archs.
>
> so i don't understand how the tests can work portably.
If you apply my patch series, you can immediately test
it on any arch you want, thanks to the test-case my patch
adds to the kernel. Please let me know on what arch it fails.
* Szabolcs Nagy <[email protected]> [2016-03-06 21:02:08 +0100]:
> * Stas Sergeev <[email protected]> [2016-03-01 00:29:03 +0300]:
> > The following patches make it possible to use swapcontext()
> > in a sighandler that works on sigaltstack.
>
> i don't think that's possible, the (obsolete) userspace
> *context functions cannot operate on kernel provided
> ucontext_t structs, so they are not usable in signal
> handlers.
>
> at least not on most target archs.
>
> so i don't understand how the tests can work portably.
>
i see the test does not use the kernel ucontext_t
and only synchronous context switch is done
sorry for the noise.