Re: [PATCH 2/8] swap: lock i_mutex for swap_writepage direct_IO

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Mon, Dec 15, 2014 at 08:56:15AM -0800, Christoph Hellwig wrote:
> On Mon, Dec 15, 2014 at 05:27:05PM +0100, Jan Kara wrote:
> > On Sun 14-12-14 21:26:56, Omar Sandoval wrote:
> > > The generic write code locks i_mutex for a direct_IO. Swap-over-NFS
> > > doesn't grab the mutex because nfs_direct_IO doesn't expect i_mutex to
> > > be held, but most direct_IO implementations do.
> >   I think you are speaking about direct IO writes only, aren't you? For DIO
> > reads we don't hold i_mutex AFAICS. And also for DIO writes we don't
> > necessarily hold i_mutex - see for example XFS which doesn't take i_mutex
> > for direct IO writes. It uses it's internal rwlock for this (see
> > xfs_file_dio_aio_write()). So I think this is just wrong.
> 
> The problem is that the use of ->direct_IO by the swap code is a gross
> layering violation.  ->direct_IO is a callback for the filesystem, and
> the swap code need to call ->read_iter instead of ->readpage and
> ->write_tier instead of ->direct_IO, and leave the locking to the
> filesystem.

The thing is, ->read_iter() and ->write_iter() might decide to fall back to 
buffered IO path.  XFS is unusual in that respect - there O_DIRECT ends up
with short write in such case.  Other filesystems, OTOH...

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>




[Index of Archives]     [Linux ARM Kernel]     [Linux ARM]     [Linux Omap]     [Fedora ARM]     [IETF Annouce]     [Bugtraq]     [Linux]     [Linux OMAP]     [Linux MIPS]     [ECOS]     [Asterisk Internet PBX]     [Linux API]