Re: [Bug #14388] keyboard under X with 2.6.31

[Linus Torvalds]

On Tue, 13 Oct 2009, Linus Torvalds wrote:
> 
>  - whoever is _reading_ the buffer, and due to memory ordering may see the 
>    update to the buffer length _before_ it actually sees the data itself. 
>    That spinlock does all the memory ordering too.

Hmm. This one looks like it's ok, because whenever we commit it, we do 
take the spinlock, so '->commit' is protected for the reader side.

>  - scrambling the data order with two writers is certainly less annoying 
>    than potentially screwing up ->used entirely, and having the memcpy's 
>    overflow the buffer. Both writers may have decided that there is enough 
>    room for each one - but that does not mean that there is enough room 
>    for _both_.

.. but this one is still true. Anybody who doesn't lock writers at a 
higher level could easily end up causing some really subtle memory 
corruption.

But maybe all users really are safe. 

		Linus
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