Re: [Xenomai-core] [PATCH] POSIX: Fix race when setting claimed bit

[Jan Kiszka <jan.kiszka@domain.hid>]

Gilles Chanteperdrix wrote:
> Jan Kiszka wrote:
>> OTOH, we can safe some text size which is precious as well. So I'm
>> convinced to go your way (with a modification):
> 
> My approach sucks: we get a silly atomic_cmpxchg if the mutex is already
> claimed, which is as least as much a common case as a currently
> unclaimed mutex. Need to think a bit. But I think a good solution is to
> re-read only if the mutex has been seen as already claimed.

That makes no difference as then we will go through the cmpxchg path anyway.

There is _no_ way around re-reading under nklock, all we can avoid is
atomic cmpxchg in the case of >1 waiters. But that would come at the
price of more complexity for all waiter.

However, let's find some solution. I bet things will look different
again when we start fiddling with a generic lock + the additional bit to
replace XNWAKEN.

Jan

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