On Sat 12-04-14 13:02:41, Ted Tso wrote:
> Al Viro pointed out that we need to make sure we only allow one
> O_APPEND write to proceed at a time so that the the s_bitmap_maxbytes
> check can be properly checked.
But this introduces lock inversion between aio_mutex and i_mutex, doesn't
it?
Honza
> Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
> ---
> fs/ext4/file.c | 46 +++++++++++++++++++++++++++++-----------------
> 1 file changed, 29 insertions(+), 17 deletions(-)
>
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index 7c8f483..c3824dd 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -98,24 +98,32 @@ ext4_file_write(struct kiocb *iocb, const struct iovec *iov,
> struct file *file = iocb->ki_filp;
> struct inode *inode = file_inode(iocb->ki_filp);
> struct blk_plug plug;
> + struct mutex *aio_mutex = NULL;
> int o_direct = file->f_flags & O_DIRECT;
> - int overwrite = 0;
> + int overwrite = 0, i_mutex_grabbed = 0;
> size_t length = iov_length(iov, nr_segs);
> ssize_t ret;
>
> BUG_ON(iocb->ki_pos != pos);
>
> + if (file->f_flags & O_APPEND) {
> + mutex_lock(&inode->i_mutex);
> + i_mutex_grabbed = 1;
> + 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;
> + (pos == sbi->s_bitmap_maxbytes && length > 0))) {
> + ret = -EFBIG;
> + goto errout;
> + }
>
> if (pos + length > sbi->s_bitmap_maxbytes) {
> nr_segs = iov_shorten((struct iovec *)iov, nr_segs,
> @@ -123,19 +131,20 @@ ext4_file_write(struct kiocb *iocb, const struct iovec *iov,
> }
> }
>
> - if (o_direct) {
> - struct mutex *aio_mutex = NULL;
> -
> - /* 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);
> - }
> + /* Unaligned direct AIO must be serialized; see comment above */
> + if (o_direct && 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);
> + }
>
> + if (!i_mutex_grabbed)
> mutex_lock(&inode->i_mutex);
> + i_mutex_grabbed = 1;
> +
> + if (o_direct) {
> if (aio_mutex)
> mutex_unlock(aio_mutex);
> blk_start_plug(&plug);
> @@ -170,11 +179,11 @@ 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, &iocb->ki_pos);
> mutex_unlock(&inode->i_mutex);
> + i_mutex_grabbed = 0;
>
> if (ret > 0) {
> ssize_t err;
> @@ -186,6 +195,9 @@ ext4_file_write(struct kiocb *iocb, const struct iovec *iov,
> if (o_direct)
> blk_finish_plug(&plug);
>
> +errout:
> + if (i_mutex_grabbed)
> + mutex_unlock(&inode->i_mutex);
> return ret;
> }
>
> --
> 1.9.0
>
> --
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--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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