Date: Sun, 11 Jul 2010 14:30:01 -0700 From: Garrett Cooper <yanegomi@gmail.com> To: Kostik Belousov <kostikbel@gmail.com> Cc: hackers@freebsd.org Subject: Re: *sigpause hanging on 8.x+ Message-ID: <AANLkTimjk7oJKlB7YCrZimMsTQtvKIxipZtfBfpIdSz3@mail.gmail.com> In-Reply-To: <20100711210843.GQ2408@deviant.kiev.zoral.com.ua> References: <AANLkTikfxu3BjQE4nnNJ-VeNSDy9vhfXEhY1XQ4jWtY4@mail.gmail.com> <20100711210843.GQ2408@deviant.kiev.zoral.com.ua>
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On Sun, Jul 11, 2010 at 2:08 PM, Kostik Belousov <kostikbel@gmail.com> wrot=
e:
> 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 com=
es up:
>>
>> $ env LD_LIBRARY_PATH=3D$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 =A0amd64
>> VM:
>> FreeBSD starr-bastion.localdomain 8.0-STABLE FreeBSD 8.0-STABLE #0
>> r207913: Tue May 11 06:21:57 UTC 2010
>> root@starr-bastion.localdomain:/usr/obj/usr/src/sys/GENERIC =A0i386
>>
>> Index: compat-43/sigcompat.c
>> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>> --- compat-43/sigcompat.c =A0 =A0 (revision 206173)
>> +++ compat-43/sigcompat.c =A0 =A0 (working copy)
>> @@ -36,6 +36,7 @@
>> =A0#include "namespace.h"
>> =A0#include <sys/param.h>
>> =A0#include <signal.h>
>> +#include <stdio.h>
>> =A0#include <string.h>
>> =A0#include "un-namespace.h"
>> =A0#include "libc_private.h"
>> @@ -102,7 +103,9 @@
>> =A0{
>> =A0 =A0 =A0 sigset_t set;
>>
>> + =A0 =A0 printf("before sigemptyset\n");
>> =A0 =A0 =A0 sigemptyset(&set);
>> + =A0 =A0 printf("before _sigsuspend\n");
>> =A0 =A0 =A0 set.__bits[0] =3D mask;
>> =A0 =A0 =A0 return (_sigsuspend(&set));
>> =A0}
>> @@ -111,10 +114,16 @@
>> =A0xsi_sigpause(int sig)
>> =A0{
>> =A0 =A0 =A0 sigset_t set;
>> + =A0 =A0 int rc;
>>
>> + =A0 =A0 printf("before sigemptyset\n");
>> =A0 =A0 =A0 sigemptyset(&set);
>> + =A0 =A0 printf("before sigaddset\n");
>> =A0 =A0 =A0 sigaddset(&set, sig);
>> - =A0 =A0 return (_sigsuspend(&set));
>> + =A0 =A0 printf("before _sigsuspend\n");
>> + =A0 =A0 rc =3D (_sigsuspend(&set));
>> + =A0 =A0 printf("after _sigsuspend\n");
>> + =A0 =A0 return rc;
>> =A0}
>>
>> =A0int
>>
>> $ cat ~/test_sigpause.c
>> #include <signal.h>
>> #include <stdio.h>
>>
>> int
>> main (void)
>> {
>> =A0 =A0 =A0 =A0 printf("0\n");
>> =A0 =A0 =A0 =A0 fflush(stdout);
>> =A0 =A0 =A0 =A0 (void) sigpause(1);
>> =A0 =A0 =A0 =A0 return 0;
>> }
>> $ cat ~/test_sigsuspend.c
>> #include <err.h>
>> #include <signal.h>
>>
>> int
>> main (void)
>> {
>> =A0 =A0 =A0 =A0 sigset_t oset;
>> =A0 =A0 =A0 =A0 sigset_t nset;
>> =A0 =A0 =A0 =A0 if (sigprocmask(1, &nset, &oset) =3D=3D -1)
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 err(1, "sigprocmask(-1, &nset, &oset)");
>> =A0 =A0 =A0 =A0 if (sigprocmask(-1, &nset, &oset) =3D=3D -1)
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 err(1, "sigprocmask(-1, &nset, &oset)");
>> =A0 =A0 =A0 =A0 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 eit=
her.
> diff --git a/lib/libc/compat-43/sigcompat.c b/lib/libc/compat-43/sigcompa=
t.c
> index c3ba30a..bab9d5c 100644
> --- a/lib/libc/compat-43/sigcompat.c
> +++ b/lib/libc/compat-43/sigcompat.c
> @@ -111,9 +111,12 @@ int
> =A0xsi_sigpause(int sig)
> =A0{
> =A0 =A0 =A0 =A0sigset_t set;
> + =A0 =A0 =A0 int error;
>
> - =A0 =A0 =A0 sigemptyset(&set);
> - =A0 =A0 =A0 sigaddset(&set, sig);
> + =A0 =A0 =A0 error =3D _sigprocmask(SIG_BLOCK, NULL, &set);
> + =A0 =A0 =A0 if (error !=3D 0)
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 return (error);
> + =A0 =A0 =A0 sigdelset(&set, sig);
> =A0 =A0 =A0 =A0return (_sigsuspend(&set));
> =A0}
Doesn't this violate the restore clause noted in the manpage?
The xsi_sigpause() function removes sig from the signal mask of the ca=
ll-
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.
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.
Thanks!
-Garrett
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