From: Andrea Arcangeli <aarcange@xxxxxxxxxx> Subject: 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@xxxxxxxxxx Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: "Dr. David Alan Gilbert" <dgilbert@xxxxxxxxxx> Cc: Alexey Perevalov <a.perevalov@xxxxxxxxxxx> Cc: Maxime Coquelin <maxime.coquelin@xxxxxxxxxx> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/mmap.c | 22 +++++++++++++++------- 1 file changed, 15 insertions(+), 7 deletions(-) diff -puN mm/mmap.c~userfaultfd-call-userfaultfd_unmap_prep-only-if-__split_vma-succeeds mm/mmap.c --- a/mm/mmap.c~userfaultfd-call-userfaultfd_unmap_prep-only-if-__split_vma-succeeds +++ a/mm/mmap.c @@ -2639,13 +2639,6 @@ int do_munmap(struct mm_struct *mm, unsi 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, unsi } 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 */ _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
