On Tue 13-11-18 17:18:58, Oleg Nesterov wrote: > On 11/13, Michal Hocko wrote: > > > > On Mon 12-11-18 12:54:45, Chanho Min wrote: > > > Suspend fails due to the exec family of functions blocking the freezer. > > > The casue is that de_thread() sleeps in TASK_UNINTERRUPTIBLE waiting for > > > all sub-threads to die, and we have the deadlock if one of them is frozen. > > > This also can occur with the schedule() waiting for the group thread leader > > > to exit if it is frozen. > > > > > > In our machine, it causes freeze timeout as bellows. > > > > > > Freezing of tasks failed after 20.010 seconds (1 tasks refusing to freeze, wq_busy=0): > > > setcpushares-ls D ffffffc00008ed70 0 5817 1483 0x0040000d > > > Call trace: > > > [<ffffffc00008ed70>] __switch_to+0x88/0xa0 > > > [<ffffffc000d1c30c>] __schedule+0x1bc/0x720 > > > [<ffffffc000d1ca90>] schedule+0x40/0xa8 > > > [<ffffffc0001cd784>] flush_old_exec+0xdc/0x640 > > > [<ffffffc000220360>] load_elf_binary+0x2a8/0x1090 > > > [<ffffffc0001ccff4>] search_binary_handler+0x9c/0x240 > > > [<ffffffc00021c584>] load_script+0x20c/0x228 > > > [<ffffffc0001ccff4>] search_binary_handler+0x9c/0x240 > > > [<ffffffc0001ce8e0>] do_execveat_common.isra.14+0x4f8/0x6e8 > > > [<ffffffc0001cedd0>] compat_SyS_execve+0x38/0x48 > > > [<ffffffc00008de30>] el0_svc_naked+0x24/0x28 > > > > > > To fix this, make de_thread() freezable. It looks safe and works fine. > > > > It's been some time since I have looked into this code so bear with me. > > One thing is not really clear to me. Why does it help to exclude this > > particular task from the freezer > > we don't exclude it, > > > when it is not sleeping in the freezer. > > Yes, it is not sleeping in __refrigerator(), but it does > > schedule(); > freezer_count(); > > so it will enter __refrigerator() right after wakeup. If it won't be woken > up we do not care, we can consider it "frozen". Right, but this is just silencing the freezing code to exclude this task, right? > > I can see how other threads need to be zapped and TASK_WAKEKILL doesn't > > do that but shouldn't we fix that instead? > > Not sure I understand, but unlikely we can (or want) to make __refrigerator() > killable. Why would that be a problem. If the kill is fatal then why to keep the killed task in the fridge? > Otherwise, how can we fix that? We can mark all threads PF_NOFREEZE and wake them up. This would require some more changes of course but wouldn't that be a more appropriate solution? Do we want to block exec for ever just because some threads are in the fridge? -- Michal Hocko SUSE Labs
