Re: 2.6.2-rc2 nfsd+xfs spins in i_size_read()

[Christoph Hellwig <hch@infradead.org>]

On Sat, Jan 31, 2004 at 09:59:06AM -0600, Steve Lord wrote:
> The vn_revalidate call is called out of linvfs_setattr,
> which is called with the i_sem held, it is also potentially called out
> of linvfs_getattr, although since the i_size is always maintained
> as it is changed, this call should not actually be updating the size.
> Possibly changing the code in vn_revalidate to do this:
> 
> 	if (i_size_read(inode) < va.va_size))
> 		i_size_write(inode, va.va_size);
> 
> Would be a good starting point, I suspect those calls from the nfs
> revalidate call are not really going to change the inode size. My
> guess is this will make your problem go away.
> 
> Probably some larger code restructure is needed so that revalidate
> knows if the i_sem is held or not at this point.

I think the right fix is to update the Linux i_size always shortly after
di_size is updated.  There's a lot of updates in the directory code while
should be handled by an i_size_write in the matching linvfs routines, and
there's a few more but we should be able to handle those without
vn_revalidate aswell.

> The O_DIRECT write case is the hard one. In XFS's internal view of
> the world, the inode size is maintained via the XFS_ILOCK, but we
> only hold that across metadata manipulation within the fs code,
> not across I/O such as a call to generic_file_aio_write_nolock.
> Right now the only way I see of dealing with that is to make
> writes which we know will extent the file hold the i_sem for
> the duration in the O_DIRECT case.

That's the more difficult case.  Any reson why you'd hold i_sem
for the whole O_DIRECT I/O instead of just for updating i_sem?

Note that the EOF zeroing code also calls i_size_write.