On Sun, Jul 11, 2010 at 3:35 PM, Garrett Cooper <yaneg...@gmail.com> wrote:
> 2010/7/11 Kostik Belousov <kostik...@gmail.com>:
>> On Sun, Jul 11, 2010 at 02:30:01PM -0700, Garrett Cooper wrote:
>>> On Sun, Jul 11, 2010 at 2:08 PM, Kostik Belousov <kostik...@gmail.com>
>>> wrote:
>>> > On Sun, Jul 11, 2010 at 12:39:39PM -0700, Garrett Cooper wrote:
>>> >> So, long story short... I've basically ported the open posix testsuite
>>> >> to FreeBSD, and one of the tests tests out sigpause. Unfortunately the
>>> >> sucker hangs on my dev box at home.
>>> >>
>>> >> I've written a short testcase that demonstrates this. It prints out:
>>> >>
>>> >> $ ~/test_sigpause
>>> >> 0
>>> >>
>>> >> And proceeds to be unresponsive to signals (except SIGSTOP / SIGKILL,
>>> >> as expected).
>>> >>
>>> >> When I monkey around with libc's compat4.3 stuff a bit, this is what
>>> >> comes up:
>>> >>
>>> >> $ env LD_LIBRARY_PATH=$PWD:/usr/src/lib/libc/../libthr ~/test_sigpause
>>> >> 0
>>> >> before sigemptyset
>>> >> before _sigsuspend
>>> >>
>>> >> So it's getting stuck after calling _sigsuspend.
>>> >>
>>> >> I tried the same thing on a i386 8-STABLE VM and it hangs as well.
>>> >>
>>> >> I tried applying similar printfs in libthr but it's not hitting that
>>> >> code at all (it's now responding to SIGTERM though, which is
>>> >> interesting, but not too interesting to me).
>>> >>
>>> >> I also wrote similar code that exercised the functionality in
>>> >> sigsuspend, by calling sigprocmask beforehand, and it works.
>>> >>
>>> >> Thoughts?
>>> >>
>>> >> -Garrett
>>> >>
>>> >> Dev machine:
>>> >> FreeBSD bayonetta.local 9.0-CURRENT FreeBSD 9.0-CURRENT #1
>>> >> r206173:209901M: Sun Jul 11 04:18:42 PDT 2010
>>> >> root@:/usr/obj/usr/src/sys/BAYONETTA amd64
>>> >> VM:
>>> >> FreeBSD starr-bastion.localdomain 8.0-STABLE FreeBSD 8.0-STABLE #0
>>> >> r207913: Tue May 11 06:21:57 UTC 2010
>>> >> r...@starr-bastion.localdomain:/usr/obj/usr/src/sys/GENERIC i386
>>> >>
>>> >> Index: compat-43/sigcompat.c
>>> >> ===================================================================
>>> >> --- compat-43/sigcompat.c (revision 206173)
>>> >> +++ compat-43/sigcompat.c (working copy)
>>> >> @@ -36,6 +36,7 @@
>>> >> #include "namespace.h"
>>> >> #include <sys/param.h>
>>> >> #include <signal.h>
>>> >> +#include <stdio.h>
>>> >> #include <string.h>
>>> >> #include "un-namespace.h"
>>> >> #include "libc_private.h"
>>> >> @@ -102,7 +103,9 @@
>>> >> {
>>> >> sigset_t set;
>>> >>
>>> >> + printf("before sigemptyset\n");
>>> >> sigemptyset(&set);
>>> >> + printf("before _sigsuspend\n");
>>> >> set.__bits[0] = mask;
>>> >> return (_sigsuspend(&set));
>>> >> }
>>> >> @@ -111,10 +114,16 @@
>>> >> xsi_sigpause(int sig)
>>> >> {
>>> >> sigset_t set;
>>> >> + int rc;
>>> >>
>>> >> + printf("before sigemptyset\n");
>>> >> sigemptyset(&set);
>>> >> + printf("before sigaddset\n");
>>> >> sigaddset(&set, sig);
>>> >> - return (_sigsuspend(&set));
>>> >> + printf("before _sigsuspend\n");
>>> >> + rc = (_sigsuspend(&set));
>>> >> + printf("after _sigsuspend\n");
>>> >> + return rc;
>>> >> }
>>> >>
>>> >> int
>>> >>
>>> >> $ cat ~/test_sigpause.c
>>> >> #include <signal.h>
>>> >> #include <stdio.h>
>>> >>
>>> >> int
>>> >> main (void)
>>> >> {
>>> >> printf("0\n");
>>> >> fflush(stdout);
>>> >> (void) sigpause(1);
>>> >> return 0;
>>> >> }
>>> >> $ cat ~/test_sigsuspend.c
>>> >> #include <err.h>
>>> >> #include <signal.h>
>>> >>
>>> >> int
>>> >> main (void)
>>> >> {
>>> >> sigset_t oset;
>>> >> sigset_t nset;
>>> >> if (sigprocmask(1, &nset, &oset) == -1)
>>> >> err(1, "sigprocmask(-1, &nset, &oset)");
>>> >> if (sigprocmask(-1, &nset, &oset) == -1)
>>> >> err(1, "sigprocmask(-1, &nset, &oset)");
>>> >> return (sigsuspend(&nset));
>>> >> }
>>> >
>>> > It seems I got a sigmask for sigpause inside the xsi_sigpause() backward.
>>> > On the other hand, I do not understand what is your issue with sigpause().
>>>
>>> The negative testcase from the open posix testsuite was setup so that
>>> setting sigpause(-1) would return -1 with EINVAL, according to the
>>> sig* manpages (-1 is an invalid signal of course). That isn't being
>>> triggered with either function today.
>>>
>>> 0 seems a bit wonky too (it's an invalid signal number).
>>>
>>> My bet is that values greater than SIGRTMAX aren't interpreted properly
>>> either.
>>
>> I will add these checks, thanks.
>
> Much obliged :)... FWIW sigprocmask fails to do the right thing in
> detecting the signal number:
>
> $ ~/test_sigprocmask
> signo = -1 result not sane (0 != -1, errno: 0 != EINVAL)
> signo = 0 result not sane (0 != -1, errno: 0 != EINVAL)
> signo = 1 result sane
> signo = 9 result sane
> signo = 17 result sane
> signo = 65 result sane
> signo = 64 result sane
> signo = 66 result not sane (0 != -1, errno: 0 != EINVAL)
>
> Would this fix that?
>
> Index: sys/kern/kern_sig.c
> ===================================================================
> --- sys/kern/kern_sig.c (revision 206173)
> +++ sys/kern/kern_sig.c (working copy)
> @@ -988,6 +988,9 @@
> struct proc *p;
> int error;
>
> + if (!_SIG_VALID(how))
> + return (-EINVAL);
> +
> p = td->td_proc;
> if (!(flags & SIGPROCMASK_PROC_LOCKED))
> PROC_LOCK(p);
*snickers* no, that definitely doesn't fix the problem:
$ ~/test_sigprocmask
signo = -1 result not sane (-1 != -1, errno: -22 != EINVAL)
signo = 0 result not sane (-1 != -1, errno: -22 != EINVAL)
signo = 1 result not sane (-1 != 0, errno: -22)
signo = 9 result not sane (-1 != 0, errno: -22)
signo = 17 result not sane (-1 != 0, errno: -22)
signo = 65 result not sane (-1 != 0, errno: -22)
signo = 64 result not sane (-1 != 0, errno: -22)
signo = 66 result not sane (-1 != -1, errno: -22 != EINVAL)
> I'll look for more low-hanging fruit.
>
>>> > diff --git a/lib/libc/compat-43/sigcompat.c
>>> > b/lib/libc/compat-43/sigcompat.c
>>> > index c3ba30a..bab9d5c 100644
>>> > --- a/lib/libc/compat-43/sigcompat.c
>>> > +++ b/lib/libc/compat-43/sigcompat.c
>>> > @@ -111,9 +111,12 @@ int
>>> > xsi_sigpause(int sig)
>>> > {
>>> > sigset_t set;
>>> > + int error;
>>> >
>>> > - sigemptyset(&set);
>>> > - sigaddset(&set, sig);
>>> > + error = _sigprocmask(SIG_BLOCK, NULL, &set);
>>> > + if (error != 0)
>>> > + return (error);
>>> > + sigdelset(&set, sig);
>>> > return (_sigsuspend(&set));
>>> > }
>>>
>>> Doesn't this violate the restore clause noted in the manpage?
>>>
>>> The xsi_sigpause() function removes sig from the signal mask of the
>>> call-
>>> ing process and suspend the calling process until a signal is received.
>>> The xsi_sigpause() function restores the signal mask of the process to
>>> its original state before returning.
>>>
>>> So if I had a sigset defined above with sig, then redefined it, I
>>> would be whacking the previous handler by passing in NULL to
>>> _sigprocmask, correct? If so, sigpause has issues too in its
>>> implementation.
>> No, not correct. Read the description of sigsuspend.
>
> Yeah, I was wrong here:
>
> The sigsuspend() system call temporarily changes the blocked signal mask
> to the set to which sigmask points, and then waits for a signal to
> arrive; on return the previous set of masked signals is restored. The
> signal mask set is usually empty to indicate that all signals are to be
> unblocked for the duration of the call.
>
>> Also note that the sigprocmask call does not change process mask.
>
> Not so sure about this though:
>
> The sigprocmask() system call examines and/or changes the current signal
> mask (those signals that are blocked from delivery). Signals are blocked
> if they are members of the current signal mask set.
>
>>> There's also some interesting SIGDELSET action going on in libthr's
>>> copy of _sigsuspend's with SIGCANCEL (apparently that's the unofficial
>>> alias for SIGRTMIN as defined by libthr), but that's a sidenote for
>>> the actual issue seen here.
>
> Here's the test app I wrote and executed above, just for future reference:
> Thanks!
> -Garrett
>
> $ cat ~/test_sigprocmask.c
> #include <errno.h>
> #include <signal.h>
> #include <stdio.h>
> #include <stdlib.h>
>
> #define TEST_SIGPROCMASK_POS(signo) do { \
> printf("signo = %d ", signo); \
> rc = sigprocmask(-1, NULL, &oset); \
> if (rc != 0) { \
> printf("result not sane (%d != 0, errno: %d)\n", \
> rc, errno); \
> } else \
> printf("result sane\n"); \
> } while (0)
>
> #define TEST_SIGPROCMASK_NEG(signo) do { \
> printf("signo = %d ", signo); \
> rc = sigprocmask(-1, NULL, &oset); \
> if (rc != -1 || errno != EINVAL) { \
> printf("result not sane (%d != -1, " \
> "errno: %d != EINVAL)\n", \
> rc, errno); \
> } else \
> printf("result sane\n"); \
> } while (0)
>
> int
> main(void)
> {
> sigset_t oset;
> int rc;
>
> TEST_SIGPROCMASK_NEG(-1);
> TEST_SIGPROCMASK_NEG(0);
> TEST_SIGPROCMASK_POS(SIGHUP);
> /* The system quietly disallows SIGKILL or SIGSTOP to be blocked. */
> TEST_SIGPROCMASK_POS(SIGKILL);
> TEST_SIGPROCMASK_POS(SIGSTOP);
> TEST_SIGPROCMASK_POS(SIGRTMIN);
> TEST_SIGPROCMASK_POS(SIGRTMIN-1);
> TEST_SIGPROCMASK_NEG(SIGRTMIN+1);
>
> return (0);
>
> }
>
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