Hi,
the following patch fixes the IMHO incorrect behavior to silently ignore attempts to set SIG_IGN on blocked signals (i.e. while running in a signal handler). See below for further explanation.
Tobias
--- kernel/signal.c.orig 2005-03-06 18:12:26.000000000 +0100
+++ kernel/signal.c 2005-03-06 18:13:08.000000000 +0100
@@ -163,14 +163,6 @@
if (t->ptrace & PT_PTRACED)
return 0;- /*
- * Blocked signals are never ignored, since the
- * signal handler may change by the time it is
- * unblocked.
- */
- if (sigismember(&t->blocked, sig))
- return 0;
-
/* Is it explicitly or implicitly ignored? */
handler = t->sighand->action[sig-1].sa.sa_handler;
return handler == SIG_IGN ||
-------- Original Message -------- Subject: PROBLEM: Ignoring blocked signals in 2.6 / 2.4 not possible Date: Sat, 26 Feb 2005 11:10:01 +0100 From: <[EMAIL PROTECTED]> To: <[email protected]> CC: <[EMAIL PROTECTED]>
Hi,
I have a question regarding blocked signals:
Is the current implementation to ignore attempts to set SIG_IGN on
blocked signals correct? The following code will go into an endless loop on kernels 2.6.10 and
2.4.25, which is IMHO not the behaviour one would expect.
-------------------- #include <signal.h> #include <sys/types.h> #include <unistd.h>
volatile int sig_received = 0;
void sigio_handler_ex (int signum, siginfo_t * siginfo, void * ucontext)
{
struct sigaction sigio_action; sig_received++;
printf("handler %d\n",sig_received); sigio_action.sa_handler = SIG_IGN;
sigio_action.sa_flags = 0;
sigemptyset(&sigio_action.sa_mask);
sigaction (SIGIO, &sigio_action, 0);kill(getpid(),SIGIO);
sigio_action.sa_sigaction = sigio_handler_ex;
sigio_action.sa_flags = SA_SIGINFO;
sigemptyset(&sigio_action.sa_mask);
sigaction (SIGIO, &sigio_action, 0);
}int main(int argc, char **argv) {
struct sigaction sigio_action;
sigio_action.sa_sigaction = sigio_handler_ex;
sigio_action.sa_flags = SA_SIGINFO;
sigemptyset(&sigio_action.sa_mask);sigaction (SIGIO, &sigio_action, 0);
kill(getpid(),SIGIO);
while (! sig_received) {
printf("waiting for signal\n");
sleep(1);
}kill(getpid(),SIGIO);
printf("%d signals handled\n",sig_received);
}--------------------
In kernel 2.6.10/kernel/signal.c sig_ignored() I found this comment: ... /* * Blocked signals are never ignored, since the * signal handler may change by the time it is * unblocked. */
if (sigismember(&t->blocked, sig))
return 0;
...so it seems this behaviour is intentional, but I don't understand it. Why should it matter if a signal handler may change while blocked, if it is ignored also, which is a user request?
The machine im writing this mail on runs with the above lines commented out without any problems so far...
All this resulted from problems a customer had with implementing a whole protocol-stack to a serially attached device in a signal-handler. After the handler ran (with SIG_IGN) there was always an extra SIGIO which triggered the handler again. Of course the real fix was to move the protocol-stack out of the handler but still it should have worked since it was a controlled environment (so there wasn't even a race between entering the handler and setting SIG_IGN). Oh and it worked for years under some realtime variant of hp-unix.
Please be so kind to CC any answer to me directly since I'm currently not subscribed to lkml.
Yours Tobias Grundmann
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