dax: Remove i_mmap_lock protection

Currently faults are protected against truncate by filesystem specific
i_mmap_sem and page lock in case of hole page. Cow faults are protected
DAX radix tree entry locking. So there's no need for i_mmap_lock in DAX
code. Remove it.

Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>

2 files changed, 5 insertions, 21 deletions

diff --git a/fs/dax.c b/fs/dax.c
index be74635e05a6..6dbe6021cab7 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -798,29 +798,19 @@ static int dax_insert_mapping(struct address_space *mapping,
                 .sector = to_sector(bh, mapping->host),
                 .size = bh->b_size,
         };
-        int error;
         void *ret;
         void *entry = *entryp;
 
-        i_mmap_lock_read(mapping);
-
-        if (dax_map_atomic(bdev, &dax) < 0) {
-                error = PTR_ERR(dax.addr);
-                goto out;
-        }
+        if (dax_map_atomic(bdev, &dax) < 0)
+                return PTR_ERR(dax.addr);
         dax_unmap_atomic(bdev, &dax);
 
         ret = dax_insert_mapping_entry(mapping, vmf, entry, dax.sector);
-        if (IS_ERR(ret)) {
-                error = PTR_ERR(ret);
-                goto out;
-        }
+        if (IS_ERR(ret))
+                return PTR_ERR(ret);
         *entryp = ret;
 
-        error = vm_insert_mixed(vma, vaddr, dax.pfn);
- out:
-        i_mmap_unlock_read(mapping);
-        return error;
+        return vm_insert_mixed(vma, vaddr, dax.pfn);
 }
 
 /**
@@ -1058,8 +1048,6 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
                 truncate_pagecache_range(inode, lstart, lend);
         }
 
-        i_mmap_lock_read(mapping);
-
         if (!write && !buffer_mapped(&bh)) {
                 spinlock_t *ptl;
                 pmd_t entry;
@@ -1148,8 +1136,6 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
         }
 
  out:
-        i_mmap_unlock_read(mapping);
-
         return result;
 
  fallback:
diff --git a/mm/memory.c b/mm/memory.c
index f09cdb8d48fa..06f552504e79 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2453,8 +2453,6 @@ void unmap_mapping_range(struct address_space *mapping,
         if (details.last_index < details.first_index)
                 details.last_index = ULONG_MAX;
 
-
-        /* DAX uses i_mmap_lock to serialise file truncate vs page fault */
         i_mmap_lock_write(mapping);
         if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap)))
                 unmap_mapping_range_tree(&mapping->i_mmap, &details);