Re: [patch] fixed both processes in D state and the /proc/ oopses [Re: [patch] Fixed the race that was oopsing Linux-2.2.0]

[MOLNAR Ingo <mingo@chiara.csoma.elte.hu>]

On Fri, 29 Jan 1999, Andrea Arcangeli wrote:

> Another way to tell the same: "how can I be sure that I am doing an
> atomic_inc(&mm->count) on a mm->count that was just > 0, and more
> important on an mm that is still allocated? "

you are misunderstanding how atomic_inc_and_test() works. The processor
guarantees this. This is the crux of SMP atomic operations. How otherwise
could we reliably build read-write spinlocks.

yes, there is no atomic_inc_and_test() yet. (it's a bit tricky to
implement but pretty much analogous to read-write locks, we probably need
to shift values down by one to get the 'just increased from -1 to 0' event
via the zero flag, and get the 'just decreased from 0 to -1' event via the
sign flag.) Also note that this is all fiction yet because we _are_
holding the kernel lock for these situations in 2.2.

-- mingo

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