Messages in this thread | | | Date | Wed, 20 Feb 2013 20:51:27 +0800 | From | Ric Mason <> | Subject | Re: [patch] mm: mlock: document scary-looking stack expansion mlock chain |
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On 02/01/2013 02:10 PM, Johannes Weiner wrote: > The fact that mlock calls get_user_pages, and get_user_pages might > call mlock when expanding a stack looks like a potential recursion.
Why expand stack need call mlock? I can't find it in the codes, could you point out to me?
> > However, mlock makes sure the requested range is already contained > within a vma, so no stack expansion will actually happen from mlock. > > Should this ever change: the stack expansion mlocks only the newly > expanded range and so will not result in recursive expansion. > > Reported-by: Al Viro <viro@ZenIV.linux.org.uk> > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> > --- > mm/mlock.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/mm/mlock.c b/mm/mlock.c > index b1647fb..78c4924 100644 > --- a/mm/mlock.c > +++ b/mm/mlock.c > @@ -185,6 +185,10 @@ long __mlock_vma_pages_range(struct vm_area_struct *vma, > if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)) > gup_flags |= FOLL_FORCE; > > + /* > + * We made sure addr is within a VMA, so the following will > + * not result in a stack expansion that recurses back here. > + */ > return __get_user_pages(current, mm, addr, nr_pages, gup_flags, > NULL, NULL, nonblocking); > }
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