[CFR][PATCH] Call proper signal handler from libthr for non-SA_SIGINFO case

[Eygene Ryabinkin]

Thu, Nov 27, 2014 at 12:14:06PM +0200, Konstantin Belousov wrote:
> On Thu, Nov 27, 2014 at 07:21:14AM +0300, Eygene Ryabinkin wrote:
> > "PROC_LOCK_ASSERT(td->td_proc, MA_OWNED);" be also present single
> > kern_sigprocmask() is called with SIGPROCMASK_PROC_LOCKED?
>
> This is what I suggested in my earlier mail. When I started looking into
> details, I decided not to do it. The reasoning is that the function
> itself touches no process state protected by the proc lock. It is
> kern_sigprocmask which works with process lock-protected data. On the
> other hand, the function works with p_sigacts, which is covered by
> ps_mtx, and I asserted it.

But sendsig_done() calls kern_sigprocmask with
(SIGPROCMASK_PROC_LOCKED | SIGPROCMASK_PS_LOCKED) thus guaranteeing
some set of locks, so its better to have some ways to support this
assertion.  I understand that the current implementation of
kern_sigprocmask() will test such an assertion, but things may change
with time.

Moreover, having all asserts at the beginning of a function makes
at least myself to immediately recognise which lock(s) should be taken
before this function is to be called, so it is a kind of a documentation.

> I believe that the following patch is due.  It is better way to ensure
> the invariants, instead of adding assert to postsig_done().

These are good, but, probably, you can do something like
{{{
PROC_LOCK_ASSERT(p, (flags & SIGPROCMASK_PROC_LOCKED) ? MA_OWNED : MA_NOTOWNED)
}}}
inside kern_sigprocmask to have a bit stronger assertion that covers
unlocked case.

> diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
> index 15638e0..502f334 100644
> --- a/sys/kern/kern_sig.c
> +++ b/sys/kern/kern_sig.c
> @@ -998,8 +998,12 @@ kern_sigprocmask(struct thread *td, int how, sigset_t *set, sigset_t *oset,
>  	int error;
>  
>  	p = td->td_proc;
> -	if (!(flags & SIGPROCMASK_PROC_LOCKED))
> +	if ((flags & SIGPROCMASK_PROC_LOCKED) != 0)
> +		PROC_LOCK_ASSERT(p, MA_OWNED);
> +	else
>  		PROC_LOCK(p);
> +	mtx_assert(&p->p_sigacts->ps_mtx, (flags & SIGPROCMASK_PS_LOCKED) != 0
> +	    ? MA_OWNED : MA_NOTOWNED);
>  	if (oset != NULL)
>  		*oset = td->td_sigmask;
>  
> @@ -2510,9 +2514,11 @@ reschedule_signals(struct proc *p, sigset_t block, int flags)
>  	int sig;
>  
>  	PROC_LOCK_ASSERT(p, MA_OWNED);
> +	ps = p->p_sigacts;
> +	mtx_assert(&ps->ps_mtx, (flags & SIGPROCMASK_PS_LOCKED) != 0 ?
> +	    MA_OWNED : MA_NOTOWNED);
>  	if (SIGISEMPTY(p->p_siglist))
>  		return;
> -	ps = p->p_sigacts;
>  	SIGSETAND(block, p->p_siglist);
>  	while ((sig = sig_ffs(&block)) != 0) {
>  		SIGDELSET(block, sig);
> 

And, being in the nit-picking mode, I'd apply the following patch
{{{
Index: sys/kern/kern_sig.c
===================================================================
--- sys/kern/kern_sig.c	(revision 275189)
+++ sys/kern/kern_sig.c	(working copy)
@@ -1043,7 +1043,7 @@
 		 * signal, possibly waking it up.
 		 */
 		if (p->p_numthreads != 1)
-			reschedule_signals(p, new_block, flags);
+			reschedule_signals(p, new_block, flags & SIGPROCMASK_PS_LOCKED);
 	}
 
 out:
}}}
because reschedule_signals() is interested only in SIGPROCMASK_PS_LOCKED,
so there is no reason to pass other bits, since it may lead to some
confusion.
-- 
Eygene Ryabinkin                                        ,,,^..^,,,
[ Life's unfair - but root password helps!           | codelabs.ru ]
[ 82FE 06BC D497 C0DE 49EC  4FF0 16AF 9EAE 8152 ECFB | freebsd.org ]
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 343 bytes
Desc: not available
URL: <http://lists.freebsd.org/pipermail/freebsd-threads/attachments/20141127/c4f67846/attachment.sig>