On 3/25/21 6:11 AM, Stefan Metzmacher wrote: > > Am 25.03.21 um 13:04 schrieb Eric W. Biederman: >> Stefan Metzmacher <metze@xxxxxxxxx> writes: >> >>> Am 25.03.21 um 12:24 schrieb Sasha Levin: >>>> From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> >>>> >>>> [ Upstream commit 4db4b1a0d1779dc159f7b87feb97030ec0b12597 ] >>>> >>>> Just like we don't allow normal signals to IO threads, don't deliver a >>>> STOP to a task that has PF_IO_WORKER set. The IO threads don't take >>>> signals in general, and have no means of flushing out a stop either. >>>> >>>> Longer term, we may want to look into allowing stop of these threads, >>>> as it relates to eg process freezing. For now, this prevents a spin >>>> issue if a SIGSTOP is delivered to the parent task. >>>> >>>> Reported-by: Stefan Metzmacher <metze@xxxxxxxxx> >>>> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> >>>> Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> >>>> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> >>>> --- >>>> kernel/signal.c | 3 ++- >>>> 1 file changed, 2 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/kernel/signal.c b/kernel/signal.c >>>> index 55526b941011..00a3840f6037 100644 >>>> --- a/kernel/signal.c >>>> +++ b/kernel/signal.c >>>> @@ -288,7 +288,8 @@ bool task_set_jobctl_pending(struct task_struct *task, unsigned long mask) >>>> JOBCTL_STOP_SIGMASK | JOBCTL_TRAPPING)); >>>> BUG_ON((mask & JOBCTL_TRAPPING) && !(mask & JOBCTL_PENDING_MASK)); >>>> >>>> - if (unlikely(fatal_signal_pending(task) || (task->flags & PF_EXITING))) >>>> + if (unlikely(fatal_signal_pending(task) || >>>> + (task->flags & (PF_EXITING | PF_IO_WORKER)))) >>>> return false; >>>> >>>> if (mask & JOBCTL_STOP_SIGMASK) >>>> >>> >>> Again, why is this proposed for 5.11 and 5.10 already? >> >> Has the bit about the io worker kthreads been backported? >> If so this isn't horrible. If not this is nonsense. No not yet - my plan is to do that, but not until we're 100% satisfied with it. > I don't know, I hope not... > > But I just tested v5.12-rc4 and attaching to > an application with iothreads with gdb is still not possible, > it still loops forever trying to attach to the iothreads. I do see the looping, gdb apparently doesn't give up when it gets -EPERM trying to attach to the threads. Which isn't really a kernel thing, but: > And I tested 'kill -9 $pidofiothread', and it feezed the whole > machine... that sounds very strange, I haven't seen anything like that running the exact same scenario. > So there's still work to do in order to get 5.12 stable. > > I'm short on time currently, but I hope to send more details soon. Thanks! I'll play with it this morning and see if I can provoke something odd related to STOP/attach. -- Jens Axboe
