[Cc Ingo and Chanho Min - the thread starts here http://lkml.kernel.org/r/0000000000004cdec6058485b2ce@xxxxxxxxxx] On Wed 20-03-19 16:00:54, Oleg Nesterov wrote: > On 03/20, Michal Hocko wrote: > > > > On Wed 20-03-19 14:24:11, Oleg Nesterov wrote: > > > On 03/20, Michal Hocko wrote: > > > > > > > > Yes we do hold the cgred mutex while calling freezable_schedule but why > > > > are we getting a warning is not really clear to me. The task should be > > > > hidden from the freezer so why do we warn at all? > > > > > > try_to_freeze() calls debug_check_no_locks_held() and this makes sense. > > > > Yes it does. But it already ignores PF_NOFREEZE tasks and I fail to see > > why is PF_FREEZER_SKIP any different. > > But they differ. PF_NOFREEZE is a "sticky" flag for kthreads. Set by default, > cleared by set_freezable() if you want a freezable kthread. > > PF_FREEZER_SKIP means that a sleeping freezable task will call try_to_freeze() > right after schedule() returns, so try_to_freeze_tasks() can safely count it as > "already frozen". But the fundamental semantic is the same right? Both might be sitting on locks that might interfere with other tasks and we should be _extra_ careful when using them. In an ideal world, none of them is really needed. So my question remains. Can we drop the warning for PF_FREEZER_SKIP tasks as well? > > it seems that skipping the task was the only viable option > > to fix suspend issues > > Yes, de_thread() should use freezable_schedule(), iow I hope we will reconsider > this (reverted) patch. As long as we do not have a better solution for the original problem then revert just because of a pointless warning is not really ideal. I am wondering why I do not see any of people acking the patch is in CC of the revert. > > as removing the cgred is way way too complicated. > > We need to do this anyway, this leads to other more serious problems... Yes but this is far away and it doesn't really seem like a stable tree material either and I am pretty sure that people on older kernels would like to not see suspend failures. Those are annoying as hell. -- Michal Hocko SUSE Labs
