On Tue, 11 Mar 2014 13:07:33 -0700 Davidlohr Bueso <davidlohr@xxxxxx> wrote:
> On Tue, 2014-03-11 at 15:39 -0400, Sasha Levin wrote:
> > Hi all,
> >
> > I've ended up deleting the log file by mistake, but this bug does seem to be important
> > so I'd rather not wait before the same issue is triggered again.
> >
> > The call chain is:
> >
> > mlock (mm/mlock.c:745)
> > __mm_populate (mm/mlock.c:700)
> > __mlock_vma_pages_range (mm/mlock.c:229)
> > VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
>
> So __mm_populate() is only called by mlock(2) and this VM_BUG_ON seems
> wrong as we call it without the lock held:
>
> up_write(¤t->mm->mmap_sem);
> if (!error)
> error = __mm_populate(start, len, 0);
> return error;
> }
__mm_populate() pretty clearly calls __mlock_vma_pages_range() under
down_read(mm->mmap_sem).
I worry about what happens if __get_user_pages decides to do
if (ret & VM_FAULT_RETRY) {
if (nonblocking)
*nonblocking = 0;
return i;
}
uh-oh, that just cleared __mm_populate()'s `locked' variable and we'll
forget to undo mmap_sem. That won't explain this result, but it's a
potential problem.
All I can think is that find_vma() went and returned a vma from a
different mm, which would be odd. How about I toss this in there?
--- a/mm/vmacache.c~a
+++ a/mm/vmacache.c
@@ -72,8 +72,10 @@ struct vm_area_struct *vmacache_find(str
for (i = 0; i < VMACACHE_SIZE; i++) {
struct vm_area_struct *vma = current->vmacache[i];
- if (vma && vma->vm_start <= addr && vma->vm_end > addr)
+ if (vma && vma->vm_start <= addr && vma->vm_end > addr) {
+ BUG_ON(vma->vm_mm != mm);
return vma;
+ }
}
return NULL;
_
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