thp: avoid breaking huge pmd invariants in case of vma_adjust failures

An huge pmd can only be mapped if the corresponding 2M virtual range is
fully contained in the vma.  At times the VM calls split_vma twice, if the
first split_vma succeeds and the second fail, the first split_vma remains
in effect and it's not rolled back.  For split_vma or vma_adjust to fail
an allocation failure is needed so it's a very unlikely event (the out of
memory killer would normally fire before any allocation failure is visible
to kernel and userland and if an out of memory condition happens it's
unlikely to happen exactly here).  Nevertheless it's safer to ensure that
no huge pmd can be left around if the vma is adjusted in a way that can't
fit hugepages anymore at the new vm_start/vm_end address.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 19 insertions, 0 deletions

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index c590b08c6fa6..827595228734 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -104,6 +104,19 @@ extern void __split_huge_page_pmd(struct mm_struct *mm, pmd_t *pmd);
 #error "hugepages can't be allocated by the buddy allocator"
 #endif
 extern int hugepage_madvise(unsigned long *vm_flags);
+extern void __vma_adjust_trans_huge(struct vm_area_struct *vma,
+                                    unsigned long start,
+                                    unsigned long end,
+                                    long adjust_next);
+static inline void vma_adjust_trans_huge(struct vm_area_struct *vma,
+                                         unsigned long start,
+                                         unsigned long end,
+                                         long adjust_next)
+{
+        if (!vma->anon_vma || vma->vm_ops || vma->vm_file)
+                return;
+        __vma_adjust_trans_huge(vma, start, end, adjust_next);
+}
 #else /* CONFIG_TRANSPARENT_HUGEPAGE */
 #define HPAGE_PMD_SHIFT ({ BUG(); 0; })
 #define HPAGE_PMD_MASK ({ BUG(); 0; })
@@ -125,6 +138,12 @@ static inline int hugepage_madvise(unsigned long *vm_flags)
         BUG();
         return 0;
 }
+static inline void vma_adjust_trans_huge(struct vm_area_struct *vma,
+                                         unsigned long start,
+                                         unsigned long end,
+                                         long adjust_next)
+{
+}
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
 #endif /* _LINUX_HUGE_MM_H */