On Tue, 12 Dec 2006 12:22:14 +0300
Dmitriy Monakhov <dmonakhov@xxxxx> wrote:
> >> @@ -2041,6 +2041,14 @@ generic_file_direct_write(struct kiocb *
> >> mark_inode_dirty(inode);
> >> }
> >> *ppos = end;
> >> + } else if (written < 0) {
> >> + loff_t isize = i_size_read(inode);
> >> + /*
> >> + * generic_file_direct_IO() may have instantiated a few blocks
> >> + * outside i_size. Trim these off again.
> >> + */
> >> + if (pos + count > isize)
> >> + vmtruncate(inode, isize);
> >> }
> >>
> >
> > XFS (at least) can call generic_file_direct_write() with i_mutex not held.
> How could it be ?
>
> from mm/filemap.c:2046 generic_file_direct_write() comment right after
> place where i want to add vmtruncate()
> /*
> * 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.
> */
>
> > And vmtruncate() expects i_mutex to be held.
> generic_file_direct_IO must called under i_mutex too
> from mm/filemap.c:2388
> /*
> * Called under i_mutex for writes to S_ISREG files. Returns -EIO if
> something
> * went wrong during pagecache shootdown.
> */
> static ssize_t
> generic_file_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
yup, the comments are wrong.
> This means XFS generic_file_direct_write() call generic_file_direct_IO()
> without
> i_mutex held too?
Think so. XFS uses blockdev_direct_IO_own_locking(). We'd need to check
with the XFS guys regarding its precise operation and what needs to be done
here.
> >
> > I guess a suitable solution would be to push this problem back up to the
> > callers: let them decide whether to run vmtruncate() and if so, to ensure
> > that i_mutex is held.
> >
> > The existence of generic_file_aio_write_nolock() makes that rather messy
> > though.
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