On 09/30, Hugh Dickins wrote: > > On Tue, 29 Sep 2015, Oleg Nesterov wrote: > > > "mm->locked_vm += grow" and vm_stat_account() in acct_stack_growth() > > are not safe; multiple threads using the same ->mm can do this at the > > same time trying to expans different vma's under down_read(mmap_sem). > expand > > This means that one of the "locked_vm += grow" changes can be lost > > and we can miss munlock_vma_pages_all() later. > > From the Cc list, I guess you are thinking this might be the fix to > the "Bad state page (mlocked)" issues Andrey and Sasha have reported. Yes, I found this when I tried to explain this problem, but I doubt this change can fix it... Firstly I think it is very unlikely that trinity hits this race. And even if mm->locked_vm is wrongly equal to zero in exit_mmap(), it seems that page_remove_rmap() should do clear_page_mlock(). But I do not understand this code enough. So if this patch can actually help I would really like to know why ;) And of course this can not explain other traces which look like mm->mmap corruption. > Acked-by: Hugh Dickins <hughd@xxxxxxxxxx> Thanks! > with some hesitation. I don't like very much that the preliminary > mm->locked_vm + grow check is still done without complete locking, > so racing threads could get more locked_vm than they're permitted; > but I'm not sure that we care enough to put page_table_lock back > over all of that (and security_vm_enough_memory wants to have final > say on whether to go ahead); even if it was that way years ago. Yes. Plus all these RLIMIT_MEMLOCK/etc and security_* checks assume that we are going to expand current->mm, but this is not necessarily true. Debugger or sys_process_vm_* can expand a foreign vma. Oleg. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>