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SubjectRe: [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U8

* Christoph Hellwig <hch@infradead.org> wrote:

> > yes, it is valid and perfectly fine code, but i'm trying to separate out
> > the simple 'mutex' functionality (99% of the semaphore users are just
> > that) and implement a 'counted semaphore' separately. This removes a
> > number of implementational constraints from mutexes.
>
> So leave the good old struct semaphore alone and introduce a mutex_t..

with nearly 1000 'struct semaphore' references in the kernel and 980 of
them being simple mutex use this is rather impractical. So i instead
went for safely detecting the 20 non-mutex uses and converting those
places. (Btw., 90% of those 20 cases can be detected safely at
compile-time (and link-time) by removing DECLARE_MUTEX_LOCKED and making
sema_init() a macro that only allows constant values of 0 and 1 and
produces a link error for other cases.)

this work is still incomplete so i'm not arguing for upstream inclusion.

(But while we did this a couple of places did turn out to use semaphores
for completion which is inefficient - we converted those to completions
and are contributing those changes to mainline. But this issue is
totally orthogonal to the issue of counted semaphores.)

Ingo
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