Commit 4805b02e authored Feb 22, 2013 by Johannes Weiner Committed by Linus Torvalds Feb 23, 2013

mm/mlock.c: document scary-looking stack expansion mlock chain



The fact that mlock calls get_user_pages, and get_user_pages might call
mlock when expanding a stack looks like a potential recursion.

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.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Hugh Dickins <hughd@google.com>
Acked-by: Michel Lespinasse <walken@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent e3790144

mm/mlock.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -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);
		}