mm: take i_mmap_lock in unmap_mapping_range() for DAX

DAX is not so special: we need i_mmap_lock to protect mapping->i_mmap.

__dax_pmd_fault() uses unmap_mapping_range() shoot out zero page from
all mappings.  We need to drop i_mmap_lock there to avoid lock deadlock.

Re-aquiring the lock should be fine since we check i_size after the
point.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 19 insertions, 16 deletions

diff --git a/fs/dax.c b/fs/dax.c
index 9ef9b80cc132..ed54efedade6 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -554,6 +554,25 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
         if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE)
                 goto fallback;
 
+        if (buffer_unwritten(&bh) || buffer_new(&bh)) {
+                int i;
+                for (i = 0; i < PTRS_PER_PMD; i++)
+                        clear_page(kaddr + i * PAGE_SIZE);
+                count_vm_event(PGMAJFAULT);
+                mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
+                result |= VM_FAULT_MAJOR;
+        }
+
+        /*
+         * If we allocated new storage, make sure no process has any
+         * zero pages covering this hole
+         */
+        if (buffer_new(&bh)) {
+                i_mmap_unlock_write(mapping);
+                unmap_mapping_range(mapping, pgoff << PAGE_SHIFT, PMD_SIZE, 0);
+                i_mmap_lock_write(mapping);
+        }
+
         /*
          * If a truncate happened while we were allocating blocks, we may
          * leave blocks allocated to the file that are beyond EOF.  We can't
@@ -568,13 +587,6 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
         if ((pgoff | PG_PMD_COLOUR) >= size)
                 goto fallback;
 
-        /*
-         * If we allocated new storage, make sure no process has any
-         * zero pages covering this hole
-         */
-        if (buffer_new(&bh))
-                unmap_mapping_range(mapping, pgoff << PAGE_SHIFT, PMD_SIZE, 0);
-
         if (!write && !buffer_mapped(&bh) && buffer_uptodate(&bh)) {
                 spinlock_t *ptl;
                 pmd_t entry;
@@ -605,15 +617,6 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
                 if ((length < PMD_SIZE) || (pfn & PG_PMD_COLOUR))
                         goto fallback;
 
-                if (buffer_unwritten(&bh) || buffer_new(&bh)) {
-                        int i;
-                        for (i = 0; i < PTRS_PER_PMD; i++)
-                                clear_page(kaddr + i * PAGE_SIZE);
-                        count_vm_event(PGMAJFAULT);
-                        mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
-                        result |= VM_FAULT_MAJOR;
-                }
-
                 result |= vmf_insert_pfn_pmd(vma, address, pmd, pfn, write);
         }