On Thu, Mar 06, 2014 at 08:32:48PM -0500, Sasha Levin wrote: > On 03/04/2014 10:53 PM, Sasha Levin wrote: > >On 03/04/2014 10:16 PM, Bob Liu wrote: > >>On Thu, Feb 27, 2014 at 11:03 PM, Kirill A. Shutemov > >><kirill.shutemov@xxxxxxxxxxxxxxx> wrote: > >>>Sasha Levin wrote: > >>>>Hi all, > >>>> > >>>>While fuzzing with trinity inside a KVM tools guest running latest -next kernel I've stumbled on the > >>>>following spew: > >>>> > >>>>[ 1428.146261] kernel BUG at mm/huge_memory.c:2785! > >>> > >>>Hm, interesting. > >>> > >>>It seems we either failed to split huge page on vma split or it > >>>materialized from under us. I don't see how it can happen: > >>> > >>> - it seems we do the right thing with vma_adjust_trans_huge() in > >>> __split_vma(); > >>> - we hold ->mmap_sem all the way from vm_munmap(). At least I don't see > >>> a place where we could drop it; > >>> > >> > >>Enable CONFIG_DEBUG_VM may show some useful information, at least we > >>can confirm weather rwsem_is_locked(&tlb->mm->mmap_sem) before > >>split_huge_page_pmd(). > > > >I have CONFIG_DEBUG_VM enabled and that code you're talking is not triggering, so mmap_sem > >is locked. > > Guess what. I've just hit it. I think this particular traceback is not a real problem: by time of exit_mm() we shouldn't race with anybody for the mm_struct. We probably could drop ->mmap_sem later in mmput() rather then in exit_mm() to fix this false positive. > It's worth keeping in mind that this is the first time I see it. Hm. That's strange exit_mmap() is called without holding ->mmap_sem. -- Kirill A. Shutemov -- 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>