ext4: move unlocked dio protection from ext4_alloc_file_blocks()

Currently ext4_alloc_file_blocks() was handling protection against
unlocked DIO. However we now need to sometimes call it under i_mmap_sem
and sometimes not and DIO protection ranks above it (although strictly
speaking this cannot currently create any deadlocks). Also
ext4_zero_range() was actually getting & releasing unlocked DIO
protection twice in some cases. Luckily it didn't introduce any real bug
but it was a land mine waiting to be stepped on.  So move DIO protection
out from ext4_alloc_file_blocks() into the two callsites.

Signed-off-by: Jan Kara <jack@suse.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 10 insertions, 11 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 5be9ca5a8a7a..65b5ada2833f 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4685,10 +4685,6 @@ static int ext4_alloc_file_blocks(struct file *file, ext4_lblk_t offset,
         if (len <= EXT_UNWRITTEN_MAX_LEN)
                 flags |= EXT4_GET_BLOCKS_NO_NORMALIZE;
 
-        /* Wait all existing dio workers, newcomers will block on i_mutex */
-        ext4_inode_block_unlocked_dio(inode);
-        inode_dio_wait(inode);
-
         /*
          * credits to insert 1 extent into extent tree
          */
@@ -4752,8 +4748,6 @@ retry:
                 goto retry;
         }
 
-        ext4_inode_resume_unlocked_dio(inode);
-
         return ret > 0 ? ret2 : ret;
 }
 
@@ -4827,6 +4821,10 @@ static long ext4_zero_range(struct file *file, loff_t offset,
         if (mode & FALLOC_FL_KEEP_SIZE)
                 flags |= EXT4_GET_BLOCKS_KEEP_SIZE;
 
+        /* Wait all existing dio workers, newcomers will block on i_mutex */
+        ext4_inode_block_unlocked_dio(inode);
+        inode_dio_wait(inode);
+
         /* Preallocate the range including the unaligned edges */
         if (partial_begin || partial_end) {
                 ret = ext4_alloc_file_blocks(file,
@@ -4835,7 +4833,7 @@ static long ext4_zero_range(struct file *file, loff_t offset,
                                  round_down(offset, 1 << blkbits)) >> blkbits,
                                 new_size, flags, mode);
                 if (ret)
-                        goto out_mutex;
+                        goto out_dio;
 
         }
 
@@ -4844,10 +4842,6 @@ static long ext4_zero_range(struct file *file, loff_t offset,
                 flags |= (EXT4_GET_BLOCKS_CONVERT_UNWRITTEN |
                           EXT4_EX_NOCACHE);
 
-                /* Wait all existing dio workers, newcomers will block on i_mutex */
-                ext4_inode_block_unlocked_dio(inode);
-                inode_dio_wait(inode);
-
                 /*
                  * Prevent page faults from reinstantiating pages we have
                  * released from page cache.
@@ -4992,8 +4986,13 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
                         goto out;
         }
 
+        /* Wait all existing dio workers, newcomers will block on i_mutex */
+        ext4_inode_block_unlocked_dio(inode);
+        inode_dio_wait(inode);
+
         ret = ext4_alloc_file_blocks(file, lblk, max_blocks, new_size,
                                      flags, mode);
+        ext4_inode_resume_unlocked_dio(inode);
         if (ret)
                 goto out;