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SubjectRe: [BUG] signal: multithread program returns with wrong errno on receiving SIGSTOP
Satoru Takeuchi wrote:
>
> 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.

It doesn't matter in this particular case, but in general it is good to
report the kernel version as well.

> 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.

Wild guess,

drivers/char/n_tty.c:job_control()

kill_pgrp(task_pgrp(current), SIGTTIN, 1);
return -ERESTARTSYS;

This is wrong. kill_pgrp()->__group_send_sig_info() sends SIGTTIN
to the thread group, but can choose any sub-thread as a target for
signal_wake_up().

This means we return ERESTARTSYS, but signal_pending() != true, bug.

Satoru, could you re-test with the untested patch below?

Oleg.

--- t/drivers/char/n_tty.c~ 2007-04-05 12:18:26.000000000 +0400
+++ t/drivers/char/n_tty.c 2007-05-28 10:57:58.000000000 +0400
@@ -1191,6 +1191,7 @@ static int job_control(struct tty_struct
is_current_pgrp_orphaned())
return -EIO;
kill_pgrp(task_pgrp(current), SIGTTIN, 1);
+ set_thread_flag(TIF_SIGPENDING);
return -ERESTARTSYS;
}
}
-
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