Hi,
On Saturday, 9 December 2006 16:35, Rafael J. Wysocki wrote:
> On Saturday, 9 December 2006 00:36, Pavel Machek wrote:
> > Hi!
> >
> > > > > I wonder if we should start a test suite ;-).
> > > > >
> > > > > > This means, however, that with this patch the behavior of a process (gdb)
> > > > > > after the resume may be different to its normal behavior, which is wrong.
> > > > >
> > > > > Yep.
> > >
> > > Okay, I think I know what to do so that it works. The above symptoms are not
> > > present with the appended patch.
> >
> > Looks good to me. Thanks for you work!
>
> Well, there's still a race possible in there, if SIGCONT comes after we have
> forced the SIGSTOP and before we call signal_wake_up().
>
> I think we should force the SIGSTOP and call signal_wake_up() without
> releasing the lock. I'll try to do something along these lines later today.
I think something like the appended patch will do.
Greetings,
Rafael
Signed-off-by: Rafael J. Wysocki <rjw at sisk.pl>
---
include/linux/sched.h | 1 +
kernel/power/process.c | 15 ++++++++-------
kernel/signal.c | 16 +++++++++++++++-
3 files changed, 24 insertions(+), 8 deletions(-)
Index: linux-2.6.19-rc6-mm2/kernel/power/process.c
===================================================================
--- linux-2.6.19-rc6-mm2.orig/kernel/power/process.c 2006-12-08 23:20:35.000000000 +0100
+++ linux-2.6.19-rc6-mm2/kernel/power/process.c 2006-12-10 00:37:24.000000000 +0100
@@ -28,8 +28,7 @@ static inline int freezeable(struct task
if ((p == current) ||
(p->flags & PF_NOFREEZE) ||
(p->exit_state == EXIT_ZOMBIE) ||
- (p->exit_state == EXIT_DEAD) ||
- (p->state == TASK_STOPPED))
+ (p->exit_state == EXIT_DEAD))
return 0;
return 1;
}
@@ -61,9 +60,13 @@ static inline void freeze_process(struct
unsigned long flags;
if (!freezing(p)) {
- freeze(p);
spin_lock_irqsave(&p->sighand->siglock, flags);
- signal_wake_up(p, 0);
+ freeze(p);
+ if (p->state == TASK_STOPPED) {
+ force_sigstop_and_wake_up(p);
+ } else {
+ signal_wake_up(p, 0);
+ }
spin_unlock_irqrestore(&p->sighand->siglock, flags);
}
}
@@ -103,9 +106,7 @@ static unsigned int try_to_freeze_tasks(
if (frozen(p))
continue;
- if (p->state == TASK_TRACED &&
- (frozen(p->parent) ||
- p->parent->state == TASK_STOPPED)) {
+ if (p->state == TASK_TRACED && frozen(p->parent)) {
cancel_freezing(p);
continue;
}
Index: linux-2.6.19-rc6-mm2/kernel/signal.c
===================================================================
--- linux-2.6.19-rc6-mm2.orig/kernel/signal.c 2006-12-08 23:20:35.000000000 +0100
+++ linux-2.6.19-rc6-mm2/kernel/signal.c 2006-12-10 00:43:39.000000000 +0100
@@ -962,6 +962,18 @@ force_sig_specific(int sig, struct task_
}
/*
+ * Force a SIGSTOP and make the task wake up.
+ *
+ * This is needed for the freezing of stopped tasks, because we want them to
+ * enter the refrigerator and be stopped again immediately after leaving it.
+ */
+void force_sigstop_and_wake_up(struct task_struct *t)
+{
+ specific_send_sig_info(SIGSTOP, SEND_SIG_FORCED, t);
+ signal_wake_up(t, 1);
+}
+
+/*
* Test if P wants to take SIG. After we've checked all threads with this,
* it's equivalent to finding no threads not blocking SIG. Any threads not
* blocking SIG were ruled out because they are not running and already
@@ -1829,7 +1841,9 @@ finish_stop(int stop_count)
read_unlock(&tasklist_lock);
}
- schedule();
+ do {
+ schedule();
+ } while (try_to_freeze());
/*
* Now we don't run again until continued.
*/
Index: linux-2.6.19-rc6-mm2/include/linux/sched.h
===================================================================
--- linux-2.6.19-rc6-mm2.orig/include/linux/sched.h 2006-12-10 00:20:07.000000000 +0100
+++ linux-2.6.19-rc6-mm2/include/linux/sched.h 2006-12-10 00:42:44.000000000 +0100
@@ -1350,6 +1350,7 @@ extern int kill_pg_info(int, struct sigi
extern void do_notify_parent(struct task_struct *, int);
extern void force_sig(int, struct task_struct *);
extern void force_sig_specific(int, struct task_struct *);
+extern void force_sigstop_and_wake_up(struct task_struct *t);
extern int send_sig(int, struct task_struct *, int);
extern void zap_other_threads(struct task_struct *p);
extern int kill_pg(pid_t, int, int);
