Hi!
Can you generate small testcase that demonstrates the problem?
> Then what would be the correct way to handle resume process. The other
> way of course is to make all the applications check the errno in case of
> failure. But that seems more more problematic then system call checking.
> What do you say?
Hmm, does that testcase behave correctly over SIGSTOP/SIGCONT? I'm not
saying kernel behaves nicely here, but perhaps fixing the apps to
check errno properly is the right thing to do? :-)
Perhaps the kernel should use ERESTARTNOHAND instead of EINTR?
The current code is more than odd:
- select() and sys_ppoll() both use ERESTARTNOHAND (i.e.:
the functions do not return to user space with SIGSTOP/SIGCONT or freezer())
- sys_poll() uses EINTR (i.e.: SIGSTOP/SIGCONT/freezer() return to user space)
Attached is a patch that switches sys_poll to ERESTARTNOHAND and a poll test
app.
Boot tested with FC6.
What do you think? With ERESTARTNOHAND, poll would only return to user space if
the app has a SIGCONT handler installed.
--
Manfred
--- 2.6/fs/select.c 2007-05-20 09:52:32.000000000 +0200
+++ build-2.6/fs/select.c 2007-07-23 22:10:21.000000000 +0200
@@ -723,7 +723,7 @@
}
err = fdcount;
if (!fdcount && signal_pending(current))
- err = -EINTR;
+ err = -ERESTARTNOHAND;
out_fds:
walk = head;
while(walk!=NULL) {
@@ -794,7 +794,7 @@
ret = do_sys_poll(ufds, nfds, &timeout);
/* We can restart this syscall, usually */
- if (ret == -EINTR) {
+ if (ret == -ERESTARTNOHAND) {
/*
* Don't restore the signal mask yet. Let do_signal() deliver
* the signal on the way back to userspace, before the signal
@@ -805,7 +805,6 @@
sizeof(sigsaved));
set_thread_flag(TIF_RESTORE_SIGMASK);
}
- ret = -ERESTARTNOHAND;
} else if (sigmask)
sigprocmask(SIG_SETMASK, &sigsaved, NULL);
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/poll.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <errno.h>
int main(int argc, char **argv)
{
int delay, ret;
struct pollfd pfd;
int pipesfd[2];
printf("sp <delay>\n");
if (argc != 2)
return 1;
delay = atoi(argv[1]);
printf("delay %d.\n", delay);
if (delay < 0 || delay > 1000)
return 2;
if (pipe(pipesfd) != 0) {
fprintf(stderr, "pipe failed with errno %d.\n", errno);
return 3;
}
pfd.fd = pipesfd[0];
pfd.events = POLLIN;
if (!fork()) {
sleep(delay);
write(pipesfd[1], "", 1);;
return 0;
}
sleep(1);
ret = poll(&pfd, 1, -1);
printf("poll returned %d.\n", ret);
if (pfd.revents)
printf(" events %8xh revents %8xh.\n", pfd.events, pfd.revents);
return 0;
}
