On Mon, Dec 18, 2006 at 04:22:44PM +0300, Dmitriy Monakhov wrote:
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 8332c77..7c571dd 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2044,8 +2044,9 @@ generic_file_direct_write(struct kiocb *
> /*
> * Sync the fs metadata but not the minor inode changes and
> * of course not the data as we did direct DMA for the IO.
> - * i_mutex is held, which protects generic_osync_inode() from
> - * livelocking. AIO O_DIRECT ops attempt to sync metadata here.
> + * i_mutex may not being held (XFS does this), if so some specific locking
> + * ordering must protect generic_osync_inode() from livelocking.
> + * AIO O_DIRECT ops attempt to sync metadata here.
> */
> if ((written >= 0 || written == -EIOCBQUEUED) &&
> ((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
> @@ -2279,6 +2280,17 @@ __generic_file_aio_write_nolock(struct k
>
> written = generic_file_direct_write(iocb, iov, &nr_segs, pos,
> ppos, count, ocount);
> + /*
> + * If host is not S_ISBLK generic_file_direct_write() may
> + * have instantiated a few blocks outside i_size files
> + * Trim these off again.
> + */
> + if (unlikely(written < 0) && !S_ISBLK(inode->i_mode)) {
> + loff_t isize = i_size_read(inode);
> + if (pos + count > isize)
> + vmtruncate(inode, isize);
> + }
> +
> if (written < 0 || written == count)
> goto out;
You comment in the first hunk that i_mutex may not be held here,
but there's no comment in __generic_file_aio_write_nolock() that the
i_mutex must be held for !S_ISBLK devices.
> @@ -2341,6 +2353,13 @@ ssize_t generic_file_aio_write_nolock(st
> ssize_t ret;
>
> BUG_ON(iocb->ki_pos != pos);
> + /*
> + * generic_file_buffered_write() may be called inside
> + * __generic_file_aio_write_nolock() even in case of
> + * O_DIRECT for non S_ISBLK files. So i_mutex must be held.
> + */
> + if (!S_ISBLK(inode->i_mode))
> + BUG_ON(!mutex_is_locked(&inode->i_mutex));
>
> ret = __generic_file_aio_write_nolock(iocb, iov, nr_segs,
> &iocb->ki_pos);
I note that you comment here in generic_file_aio_write_nolock(),
but it's not immediately obvious that this is refering to the
vmtruncate() call in __generic_file_aio_write_nolock().
IOWs, wouldn't it be better to put this comment and check in
__generic_file_aio_write_nolock() directly above the vmtruncate()
call that cares about this?
> @@ -2383,8 +2402,8 @@ ssize_t generic_file_aio_write(struct ki
> EXPORT_SYMBOL(generic_file_aio_write);
>
> /*
> - * Called under i_mutex for writes to S_ISREG files. Returns -EIO if something
> - * went wrong during pagecache shootdown.
> + * May be called without i_mutex for writes to S_ISREG files. XFS does this.
> + * Returns -EIO if something went wrong during pagecache shootdown.
> */
Not sure you need to say "XFS does this" - other filesystems may do this
in the future.....
Cheers,
Dave.
--
Dave Chinner
Principal Engineer
SGI Australian Software Group
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