On Mon, 28 May 2007 11:32:00 +0900 Satoru Takeuchi <[email protected]> wrote:
> Hi,
>
> I found a bug on signal subsystem. If there is some multithread program
> and one of the thread is blocking on the system call, it returns with
> wrong errno on receiving SIGSTOP and following SIGCONT.
>
> Arch dependency
> ===============
>
> succeed to reproduce: i386, ia64
> Unknown: any other arch
>
> # I suspect that this problem occur on any arch...
>
> How to reproduce
> ================
>
> This process needs 2 terminals, term A and term B.
>
> 1. issue the test program (attached on this mail) from term A.
>
> $ ./mt-wrong-errno
>
> 2. send SIGSTOP to test program from term B.
>
> $ ps a
> ...
> 9685 pts/3 Sl+ 0:00 ./mt-wrong-errno
> 9688 pts/4 R+ 0:00 ps a
> $ kill -STOP 9685
>
> 3. send SIGCONT to test program from term B.
>
> $ kill -CONT 9685
>
> Expected Result
> ===============
>
> `./mt-wrong-errno' restarts read syscall (and stop again by receiving
> SIGTTIN).
>
> Actual Result
> =============
>
> `./mt-wrong-errno' returns with wrong errno 512 means ERESTARTSYS.
> The comment on include/linux/errno.h says "this errno should never be
> seen by user program." So it's definitely a bug.
>
> output of term A
> ----------------
>
> $ ./mt-wrong-errno
>
> [1]+ Stopped ./mt-wrong-errno
> $ errno = 512
>
> output of term B
> ----------------
>
> $ ps a
> ...
> 9685 pts/3 Sl+ 0:00 ./mt-wrong-errno
> 9688 pts/4 R+ 0:00 ps a
> $ kill -STOP 9685
> $ kill -CONT 9685
>
>
> This problem can always reproduce, so it's no timing issue. I suspect
> that group_stop_count counting mechanism has something wrong and
> signal handling is canceled erroneously.
>
> Any hints or patch itself are welcome.
>
> Thanks,
>
> Satoru
>
> -------------------------------------------------------------------------------
> /*
> * mt-wrong-errno.c
> *
> * Copyright 2007 Satoru Takeuchi <[email protected]>
> *
> * This software may be used and distributed according to the terms
> * of the GNU General Public License, incorporated herein by reference.
> *
> */
>
> #include <sys/types.h>
> #include <pthread.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <err.h>
> #include <unistd.h>
> #include <stdio.h>
> #include <errno.h>
>
> void *thread_fn(void *arg)
> {
> char c;
> int ret;
>
> ret = read(STDIN_FILENO, &c, 1);
> if (ret < 0)
> printf("errno = %d\n", errno);
>
> return NULL;
> }
>
> int main(int argc, char *argv[])
> {
> pthread_t t;
>
> if (pthread_create(&t, NULL, thread_fn, NULL))
> err(EXIT_FAILURE, "pthread_create() failed\n");
>
> if (pthread_join(t, NULL))
> warn("pthread_join() failed\n");
> }
What kernel versions is this occurring on?
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