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 3736d9d..7d55a59 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -107,16 +107,36 @@
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 @@
}
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 @@
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 @@
if (o_direct)
blk_finish_plug(&plug);
+errout:
if (aio_mutex)
mutex_unlock(aio_mutex);
return ret;