ext4: allocate entire range in zero range

commit 0f2af21aae11972fa924374ddcf52e88347cf5a8 upstream.

Currently there is a bug in zero range code which causes zero range
calls to only allocate block aligned portion of the range, while
ignoring the rest in some cases.

In some cases, namely if the end of the range is past i_size, we do
attempt to preallocate the last nonaligned block. However this might
cause kernel to BUG() in some carefully designed zero range requests
on setups where page size > block size.

Fix this problem by first preallocating the entire range, including
the nonaligned edges and converting the written extents to unwritten
in the next step. This approach will also give us the advantage of
having the range to be as linearly contiguous as possible.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: Moritz Muehlenhoff <jmm@debian.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 2a4b4f3b1ae2edd444bdc018f0b8ee7b42ff6f05..cdfe574ba3d9dc256be212a3d234b94bd540b2f9 100644 (file)
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4795,12 +4795,6 @@ static long ext4_zero_range(struct file *file, loff_t offset,
        else
                max_blocks -= lblk;
 
-       flags = EXT4_GET_BLOCKS_CREATE_UNWRIT_EXT |
-               EXT4_GET_BLOCKS_CONVERT_UNWRITTEN |
-               EXT4_EX_NOCACHE;
-       if (mode & FALLOC_FL_KEEP_SIZE)
-               flags |= EXT4_GET_BLOCKS_KEEP_SIZE;
-
        mutex_lock(&inode->i_mutex);
 
        /*
@@ -4817,15 +4811,28 @@ static long ext4_zero_range(struct file *file, loff_t offset,
                ret = inode_newsize_ok(inode, new_size);
                if (ret)
                        goto out_mutex;
-               /*
-                * If we have a partial block after EOF we have to allocate
-                * the entire block.
-                */
-               if (partial_end)
-                       max_blocks += 1;
        }
 
+       flags = EXT4_GET_BLOCKS_CREATE_UNWRIT_EXT;
+       if (mode & FALLOC_FL_KEEP_SIZE)
+               flags |= EXT4_GET_BLOCKS_KEEP_SIZE;
+
+       /* Preallocate the range including the unaligned edges */
+       if (partial_begin || partial_end) {
+               ret = ext4_alloc_file_blocks(file,
+                               round_down(offset, 1 << blkbits) >> blkbits,
+                               (round_up((offset + len), 1 << blkbits) -
+                                round_down(offset, 1 << blkbits)) >> blkbits,
+                               new_size, flags, mode);
+               if (ret)
+                       goto out_mutex;
+
+       }
+
+       /* Zero range excluding the unaligned edges */
        if (max_blocks > 0) {
+               flags |= (EXT4_GET_BLOCKS_CONVERT_UNWRITTEN |
+                         EXT4_EX_NOCACHE);
 
                /* Now release the pages and zero block aligned part of pages*/
                truncate_pagecache_range(inode, start, end - 1);