Commit 2376dd7c authored Sep 06, 2017 by Andrea Arcangeli Committed by Linus Torvalds Sep 06, 2017

userfaultfd: call userfaultfd_unmap_prep only if __split_vma succeeds

A __split_vma is not a worthy event to report, and it's definitely not a
unmap so it would be incorrect to report unmap for the whole region to
the userfaultfd manager if a __split_vma fails.

So only call userfaultfd_unmap_prep after the __vma_splitting is over
and do_munmap cannot fail anymore.

Also add unlikely because it's better to optimize for the vast majority
of apps that aren't using userfaultfd in a non cooperative way.  Ideally
we should also find a way to eliminate the branch entirely if
CONFIG_USERFAULTFD=n, but it would complicate things so stick to
unlikely for now.

Link: http://lkml.kernel.org/r/20170802165145.22628-5-aarcange@redhat.com


Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Alexey Perevalov <a.perevalov@samsung.com>
Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent d312cb1e

mm/mmap.c

+15 −7

Original line number	Diff line number	Diff line
		@@ -2639,13 +2639,6 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
		if (vma->vm_start >= end)
		return 0;

		if (uf) {
		int error = userfaultfd_unmap_prep(vma, start, end, uf);

		if (error)
		return error;
		}

		/*
		* If we need to split any vma, do it now to save pain later.
		*
		@@ -2679,6 +2672,21 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
		}
		vma = prev ? prev->vm_next : mm->mmap;

		if (unlikely(uf)) {
		/*
		* If userfaultfd_unmap_prep returns an error the vmas
		* will remain splitted, but userland will get a
		* highly unexpected error anyway. This is no
		* different than the case where the first of the two
		* __split_vma fails, but we don't undo the first
		* split, despite we could. This is unlikely enough
		* failure that it's not worth optimizing it for.
		*/
		int error = userfaultfd_unmap_prep(vma, start, end, uf);
		if (error)
		return error;
		}

		/*
		* unlock any mlock()ed ranges before detaching vmas
		*/