On 1/29/19 4:58 AM, Arnd Bergmann wrote:
> On Tue, Jan 29, 2019 at 7:30 AM Christoph Hellwig <hch@xxxxxx> wrote:
>>
>> On Mon, Jan 28, 2019 at 11:25:12AM -0700, Jens Axboe wrote:
>>>> Especially with poll support now in the series, don't we need a ѕigmask
>>>> argument similar to pselect/ppoll/io_pgetevents now to deal with signal
>>>> blocking during waiting for events?
>>>
>>> Is there any way to avoid passing in the sigset_t size? If it's just a
>>> 32-bit/64-bit thing, surely the in_compat_syscall() could cover it? Or
>>> are there other cases that need to be catered to?
>>
>> As far as I can tell we never look at it, never looked at it and don't
>> have any plans to look at it anytime soon. But when I tried to omit
>> it for io_pgetevents I got stong pushback and thus had to add the
>> crazy double indirection calling convention.
>
> Deepa has recently reworked the handling for the sigset_t handling
> to be more consistent. As I understand it, we only ever check the
> size argument to ensure that user and kernel space agree on
> the size, as it there had been some historic differences.
>
> If you pass a signal mask to a syscall, you should now just use the
> set_user_sigmask()/set_compat_user_sigmask()/restore_user_sigmask()
> helpers. The compat version is required for the incompatible bit order
> between 32-bit and 64-bit big-endian architectures (on little-endian, compat
> and native signal masks are compatible), and to deal with the one
> architecture that has an _NSIG defined to something other than 64:
> MIPS uses 128 because of a historic accident.
>
> I think Deepa originally suggested combining set_user_sigmask()
> and set_compat_user_sigmask(), using an in_compat_syscall()
> check. This would let us simplify a number of compat syscalls
> (ppoll, ppoll_time32, pselect6, pselect6_time32, epoll_pwait()
> io_pgetevents_time64, io_pgetevents_time32). I advised against
> changing it at the time for consistency with other compat syscalls,
> but it's something we can still do now.
That's good info. I am currently using set_user_sigmask() for it.
I'd really like to avoid having to pass in a sigset_t size for the
system call, however. What's the best way of achieving that? Can I get
away with doing something like this:
if (in_compat_syscall()) {
const compat_sigset_t __user *compat_sig;
compat_sig = (const compat_sigset_t __user *) sig;
ret = set_compat_user_sigmask(compat_sig, &ksigmask,
&sigsaved, _NSIG_WORDS);
} else {
ret = set_user_sigmask(sig, &ksigmask, &sigsaved,
_NSIG_WORDS);
}
--
Jens Axboe
