On Fri 08-04-22 23:41:11, Thomas Gleixner wrote: [...] > Coming back to your original question. > > What's the difference between a process shared and a process private > futex in the context of a multi threaded process? > > - The process shared must obviously have a shared mapping > > - The process private has no need for a shared mapping because > all threads share the same address space. > > What do they have in common? > > - All of them are threads in the kernel POV > > - All of them care about the unexpected exit/death of some other > thread vs. locking > > So why would a process private robust mutex be any different from a > process shared one? Purely from the OOM POV they are slightly different because the OOM killer always kills all threads which share the mm with the selected victim (with an exception of the global init - see __oom_kill_process). Note that this is including those threads which are not sharing signals handling. So clobbering private locks shouldn't be observable to an alive thread unless I am missing something. On the other hand I do agree that delayed oom_reaper execution is a reasonable workaround and the most simplistic one. If I understand your example code then we would need to evaluate the whole robust list and that is simply not feasible because that would require a #PF in general case. HTH -- Michal Hocko SUSE Labs
