Am 25.03.21 um 14:38 schrieb Jens Axboe: > 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. Do you understand why the patches where autoselected for 5.11 and 5.10? >> 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: Maybe we need to remove the iothreads from /proc/pid/tasks/ >> 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. Thanks! Somehow I have the impression that your same_thread_group_account patch may fix a lot of things... metze
