linux-kernel - Re: [patch 2/3] splice: implement default splice

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Message-ID: <20090514180003.GU4140@kernel.dk>
Date:	Thu, 14 May 2009 20:00:03 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	akpm@...ux-foundation.org, max@...mpel.org,
	torvalds@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 2/3] splice: implement default splice_read method

On Thu, May 14 2009, Miklos Szeredi wrote:
> On Thu, 14 May 2009, Jens Axboe wrote:
> 
> > > The bigger problem is that the default_file_splice_write()
> > > implementation in the other patch does the same (it calls
> > > buf->ops->map() on all buffers).
> > 
> > Yep that's even worse, as that should go BUG() pretty much immediately
> > when the KM_USER0 slot is reused!
> 
> No, ->map() calls plain kmap() if "atomic" argument is zero.
> Nevertheless the deadlock due to multiple kmaps is still possible.

It's buggy either way, didn't check whether you used atomic maps or not.

> > > Hmm.  Simple solution would be to do a write() for each buffer.  But
> > > this only affects HIGHMEM kernels, so it's a bit pointless to do that
> > > on all archs.  Sigh...
> > 
> > It is unfortunate, we are going to be stuck with that for some time
> > still...
> 
> I'm going to be offline till next monday, I'll post a fix after that.

Until monday, or the monday after? I'm tempted to revert the
readv/writev part until this is settled, we cannot ship it as-is.

-- 
Jens Axboe

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