ext4: fix locking for O_APPEND writes

Al Viro pointed out that locking for O_APPEND writes was problematic,
since the location of the write isn't known until after we take the
i_mutex, which impacts the ext4_unaligned_aio() and s_bitmap_maxbytes
check.

For O_APPEND always assume that the write is unaligned so call
ext4_unwritten_wait().  And to solve the second problem, take the
i_mutex earlier before we start the s_bitmap_maxbytes check.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 3736d9dfe3258a2303e310ae837290627e8b887b..7d55a591deba11e5752e074d5a1d2792d8ae8616 100644 (file)
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -106,17 +106,37 @@ ext4_file_write(struct kiocb *iocb, const struct iovec *iov,
 
        BUG_ON(iocb->ki_pos != pos);
 
+       /*
+        * Unaligned direct AIO must be serialized; see comment above
+        * In the case of O_APPEND, assume that we must always serialize
+        */
+       if (o_direct &&
+           ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS) &&
+           !is_sync_kiocb(iocb) &&
+           (file->f_flags & O_APPEND ||
+            ext4_unaligned_aio(inode, iov, nr_segs, pos))) {
+               aio_mutex = ext4_aio_mutex(inode);
+               mutex_lock(aio_mutex);
+               ext4_unwritten_wait(inode);
+       }
+
+       mutex_lock(&inode->i_mutex);
+       if (file->f_flags & O_APPEND)
+               iocb->ki_pos = pos = i_size_read(inode);
+
        /*
         * If we have encountered a bitmap-format file, the size limit
         * is smaller than s_maxbytes, which is for extent-mapped files.
         */
-
        if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
                struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 
-               if ((pos > sbi->s_bitmap_maxbytes ||
-                   (pos == sbi->s_bitmap_maxbytes && length > 0)))
-                       return -EFBIG;
+               if ((pos > sbi->s_bitmap_maxbytes) ||
+                   (pos == sbi->s_bitmap_maxbytes && length > 0)) {
+                       mutex_unlock(&inode->i_mutex);
+                       ret = -EFBIG;
+                       goto errout;
+               }
 
                if (pos + length > sbi->s_bitmap_maxbytes) {
                        nr_segs = iov_shorten((struct iovec *)iov, nr_segs,
@@ -125,16 +145,6 @@ ext4_file_write(struct kiocb *iocb, const struct iovec *iov,
        }
 
        if (o_direct) {
-               /* Unaligned direct AIO must be serialized; see comment above */
-               if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS) &&
-                   !is_sync_kiocb(iocb) &&
-                   ext4_unaligned_aio(inode, iov, nr_segs, pos)) {
-                       aio_mutex = ext4_aio_mutex(inode);
-                       mutex_lock(aio_mutex);
-                       ext4_unwritten_wait(inode);
-               }
-
-               mutex_lock(&inode->i_mutex);
                blk_start_plug(&plug);
 
                iocb->private = &overwrite;
@@ -167,8 +177,7 @@ ext4_file_write(struct kiocb *iocb, const struct iovec *iov,
                        if (err == len && (map.m_flags & EXT4_MAP_MAPPED))
                                overwrite = 1;
                }
-       } else
-               mutex_lock(&inode->i_mutex);
+       }
 
        ret = __generic_file_aio_write(iocb, iov, nr_segs);
        mutex_unlock(&inode->i_mutex);
@@ -183,6 +192,7 @@ ext4_file_write(struct kiocb *iocb, const struct iovec *iov,
        if (o_direct)
                blk_finish_plug(&plug);
 
+errout:
        if (aio_mutex)
                mutex_unlock(aio_mutex);
        return ret;