Messages in this thread | | | Subject | Re: mm: NULL ptr deref in unlink_file_vma | From | Davidlohr Bueso <> | Date | Mon, 22 Dec 2014 11:04:32 -0800 |
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On Mon, 2014-12-22 at 20:04 +0200, Kirill A. Shutemov wrote: > [ fixed Davidlohr's address. ] > > On Mon, Dec 22, 2014 at 08:01:02PM +0200, Kirill A. Shutemov wrote: > > On Mon, Dec 22, 2014 at 10:04:02AM -0500, Sasha Levin wrote: > > > Hi all, > > > > > > While fuzzing with trinity inside a KVM tools guest running the latest -next > > > kernel, I've stumbled on the following spew: > > > > > > [ 432.376425] BUG: unable to handle kernel NULL pointer dereference at 0000000000000038 > > > [ 432.378876] IP: down_write (./arch/x86/include/asm/rwsem.h:105 ./arch/x86/include/asm/rwsem.h:121 kernel/locking/rwsem.c:71) > > > > Looks like vma->vm_file->mapping is NULL. Somebody freed ->vm_file from > > under us? > > > > I suspect Davidlohr's patchset on i_mmap_lock, but I cannot find any code > > path which could lead to the crash.
Sasha, does this still occur if you revert c8475d144abb?
> > I've noticed one strange code path, which probably is not related to the > > issue: > > > > unmap_mapping_range() > > i_mmap_lock_read(mapping); > > unmap_mapping_range_tree() > > unmap_mapping_range_vma() > > zap_page_range_single() > > unmap_single_vma() > > if (unlikely(is_vm_hugetlb_page(vma))) { > > i_mmap_lock_write(vma->vm_file->f_mapping);
Right, this is would be completely bogus. But the deadlock cannot happen in reality as hugetlb uses its own handlers and thus never calls unmap_mapping_range.
Thanks, Davidlohr
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