diff options
| author | Andrea Arcangeli | 2017-09-06 16:23:53 -0700 |
|---|---|---|
| committer | Linus Torvalds | 2017-09-06 17:27:29 -0700 |
| commit | 2376dd7ceddae67432db055ff3f2b7f4122a919d (patch) | |
| tree | 4a2eb51d3885c74c8ea3b9869f869884ad130fca /mm/mmap.c | |
| parent | d312cb1e4884c606bafe6499fade2f91ccc2e944 (diff) | |
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>
Diffstat (limited to 'mm/mmap.c')
| -rw-r--r-- | mm/mmap.c | 22 |
1 files changed, 15 insertions, 7 deletions
diff --git a/mm/mmap.c b/mm/mmap.c index 9800e29763f4..52f6c6b18f40 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -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 */ |