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37f8173dd locking/atomics: Flip fallbacks and instrumentation ... Browse Code »

Currently instrumentation of atomic primitives is done at the architecture
level, while composites or fallbacks are provided at the generic level.

The result is that there are no uninstrumented variants of the
fallbacks. Since there is now need of such variants to isolate text poke
from any form of instrumentation invert this ordering.

Doing this means moving the instrumentation into the generic code as
well as having (for now) two variants of the fallbacks.

Notes:

- the various *cond_read* primitives are not proper fallbacks
and got moved into linux/atomic.c. No arch_ variants are
generated because the base primitives smp_cond_load*()
are instrumented.

- once all architectures are moved over to arch_atomic_ one of the
fallback variants can be removed and some 2300 lines reclaimed.

- atomic_{read,set}*() are no longer double-instrumented

Reported-by: Thomas Gleixner
Signed-off-by: Peter Zijlstra (Intel)
Signed-off-by: Thomas Gleixner
Acked-by: Mark Rutland
Link: https://lkml.kernel.org/r/20200505134058.769149955@linutronix.de

Peter Zijlstra
2020-06-11 14:03:24 +0800

try_cmpxchg 254 Bytes

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cat <<EOF
static __always_inline bool
${arch}${atomic}_try_cmpxchg${order}(${atomic}_t *v, ${int} *old, ${int} new)
{
	${int} r, o = *old;
	r = ${arch}${atomic}_cmpxchg${order}(v, o, new);
	if (unlikely(r != o))
		*old = r;
	return likely(r == o);
}
EOF