2.6.17-mm3: swsusp fails when process is debugged by ptrace

2.6.17-mm3: swsusp fails when process is debugged by ptrace

[Jeremy Fitzhardinge]

If I try to suspend the machine while a process debug-stopped by ptrace, 
suspend fails:

PM: Preparing system for mem sleep
Freezing cpus ...
Breaking affinity for irq 0
Breaking affinity for irq 1
Breaking affinity for irq 12
Breaking affinity for irq 23
CPU 1 is now offline
SMP alternatives: switching to UP code
CPU1 is down
Stopping tasks: ==========================================================================================================================================================
 stopping tasks timed out after 20 seconds (13 tasks remaining):
  khubd
  kseriod
  pdflush
  pdflush
  kswapd0
  kprefetchd
  pccardd
  kirqd
  kjournald
  kauditd
  knodemgrd_0
  kjournald
  test-vsnprintf
Restarting tasks...<6> Strange, khubd not stopped
 Strange, kseriod not stopped
 Strange, pdflush not stopped
 Strange, pdflush not stopped
 Strange, kswapd0 not stopped
 Strange, kprefetchd not stopped
 Strange, pccardd not stopped
 Strange, kirqd not stopped
 Strange, kjournald not stopped
 Strange, kauditd not stopped
 Strange, knodemgrd_0 not stopped
 Strange, kjournald not stopped
 Strange, test-vsnprintf not stopped
 done
Thawing cpus ...

In this case, test-vsnprintf is stopped in a breakpoint in gdb.  If I 
quit it, then suspend works as expected.

    J

Re: 2.6.17-mm3: swsusp fails when process is debugged by ptrace

[Pavel Machek]

Hi!

> If I try to suspend the machine while a process debug-stopped by ptrace, 
> suspend fails:
> 
> PM: Preparing system for mem sleep
> Freezing cpus ...
> Breaking affinity for irq 0
> Breaking affinity for irq 1
> Breaking affinity for irq 12
> Breaking affinity for irq 23
> CPU 1 is now offline
> SMP alternatives: switching to UP code
> CPU1 is down
> Stopping tasks: 
> ==========================================================================================================================================================
> stopping tasks timed out after 20 seconds (13 tasks remaining):
>  khubd
>  kseriod
>  pdflush
>  pdflush
>  kswapd0
>  kprefetchd
>  pccardd
>  kirqd
>  kjournald
>  kauditd
>  knodemgrd_0
>  kjournald
>  test-vsnprintf
> Restarting tasks...<6> Strange, khubd not stopped
> Strange, kseriod not stopped
> Strange, pdflush not stopped
> Strange, pdflush not stopped
> Strange, kswapd0 not stopped
> Strange, kprefetchd not stopped
> Strange, pccardd not stopped
> Strange, kirqd not stopped
> Strange, kjournald not stopped
> Strange, kauditd not stopped
> Strange, knodemgrd_0 not stopped
> Strange, kjournald not stopped
> Strange, test-vsnprintf not stopped
> done
> Thawing cpus ...
> 
> In this case, test-vsnprintf is stopped in a breakpoint in gdb.  If I 
> quit it, then suspend works as expected.

Does it also happen when you do strace? ...I remember trying to solve
that, but 2.6.17-mm3 is very recent...?
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: 2.6.17-mm3: swsusp fails when process is debugged by ptrace

[Jeremy Fitzhardinge]

Pavel Machek wrote:
> Does it also happen when you do strace? ...I remember trying to solve
> that, but 2.6.17-mm3 is very recent...?

I could suspend while running "strace sleep 100" without any problem.

I think the issue is when the process is blocked in T state,
freeze_process() tries to kick the process with signal_wake_up(p, /*
resume=0 */ 0), but with resume=0 it will only wake processes in
TASK_INTERRUPTIBLE state.  With resume=1, it will also kick STOPPED and
TRACED processes.  I also tried suspending while I had a process in T
state caused by kill -STOP, and that worked, so some part of the puzzle
is still missing.

I noticed that when I ran sleep 100 under strace over the suspend/resume
cycle, its nanosleep() syscall was interrupted and not restarted.

    J

Re: 2.6.17-mm3: swsusp fails when process is debugged by ptrace

[Pavel Machek]

Hi!

> >Does it also happen when you do strace? ...I remember trying to solve
> >that, but 2.6.17-mm3 is very recent...?
> 
> I could suspend while running "strace sleep 100" without any problem.
> 
> I think the issue is when the process is blocked in T state,
> freeze_process() tries to kick the process with signal_wake_up(p, /*
> resume=0 */ 0), but with resume=0 it will only wake processes in
> TASK_INTERRUPTIBLE state.  With resume=1, it will also kick STOPPED and
> TRACED processes.  I also tried suspending while I had a process in T
> state caused by kill -STOP, and that worked, so some part of the puzzle
> is still missing.

So... does signal_wake_up(p, 1) fix it?

> I noticed that when I ran sleep 100 under strace over the suspend/resume
> cycle, its nanosleep() syscall was interrupted and not restarted.

I'm afraid there may be more problems lurking in the refrigerator.

(If this is going to take more than few mail iterations... perhaps you
should start bug at bugzilla.kernel.org?)
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: 2.6.17-mm3: swsusp fails when process is debugged by ptrace

[Jeremy Fitzhardinge]

Pavel Machek wrote:
> So... does signal_wake_up(p, 1) fix it?
>   

I'll try it out.

> I'm afraid there may be more problems lurking in the refrigerator.
>
> (If this is going to take more than few mail iterations... perhaps you
> should start bug at bugzilla.kernel.org?)
>   
http://bugzilla.kernel.org/show_bug.cgi?id=6787

    J