mm/nommu: share the i_mmap_rwsem

Shrinking/truncate logic can call nommu_shrink_inode_mappings() to verify
that any shared mappings of the inode in question aren't broken (dead
zone).  afaict the only user being ramfs to handle the size change
attribute.

Pretty much a no-brainer to share the lock.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: "Kirill A. Shutemov" <kirill@shutemov.name>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 5 deletions

diff --git a/mm/nommu.c b/mm/nommu.c
index 52a576553581..cd519e1cd8a7 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -2094,14 +2094,14 @@ int nommu_shrink_inode_mappings(struct inode *inode, size_t size,
         high = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 
         down_write(&nommu_region_sem);
-        i_mmap_lock_write(inode->i_mapping);
+        i_mmap_lock_read(inode->i_mapping);
 
         /* search for VMAs that fall within the dead zone */
         vma_interval_tree_foreach(vma, &inode->i_mapping->i_mmap, low, high) {
                 /* found one - only interested if it's shared out of the page
                  * cache */
                 if (vma->vm_flags & VM_SHARED) {
-                        i_mmap_unlock_write(inode->i_mapping);
+                        i_mmap_unlock_read(inode->i_mapping);
                         up_write(&nommu_region_sem);
                         return -ETXTBSY; /* not quite true, but near enough */
                 }
@@ -2113,8 +2113,7 @@ int nommu_shrink_inode_mappings(struct inode *inode, size_t size,
          * we don't check for any regions that start beyond the EOF as there
          * shouldn't be any
          */
-        vma_interval_tree_foreach(vma, &inode->i_mapping->i_mmap,
-                                  0, ULONG_MAX) {
+        vma_interval_tree_foreach(vma, &inode->i_mapping->i_mmap, 0, ULONG_MAX) {
                 if (!(vma->vm_flags & VM_SHARED))
                         continue;
 
@@ -2129,7 +2128,7 @@ int nommu_shrink_inode_mappings(struct inode *inode, size_t size,
                 }
         }
 
-        i_mmap_unlock_write(inode->i_mapping);
+        i_mmap_unlock_read(inode->i_mapping);
         up_write(&nommu_region_sem);
         return 0;
 }