Re: [patch v3] splice: fix race with page invalidation

[Linus Torvalds]

On Wed, 30 Jul 2008, Linus Torvalds wrote:
> 
> Personally, I think the right approach is to just realize that splice() is 
> _not_ a write() system call, and never will be. If you need synchronous 
> writing, you simply shouldn't use splice().

Side note: in-kernel users could probably do somethign about this. IOW, if 
there's some in-kernel usage (and yes, knfsd would be a prime example), 
that one may actually be able to do things that a _user_level user of 
splice() could never do.

That includes things like getting the inode semaphore over a write (so 
that you can guarantee that pages that are in flight are not modified, 
except again possibly by other mmap users), and/or a per-page callback for 
when splice() is done with a page (so that you could keep the page locked 
while it's getting spliced, for example).

And no, we don't actually have that either, of course.

			Linus
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