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Documentation/atomic_t.txt: Clarify pure non-rmw usage 

Clarify that pure non-RMW usage of atomic_t is pointless, there is
nothing 'magical' about atomic_set() / atomic_read().

This is something that seems to confuse people, because I happen upon it
semi-regularly.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190524115231.GN2623@hirez.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
alistair/sunxi64-5.4-dsi
Peter Zijlstra 2019-05-24 13:52:31 +02:00 committed by Ingo Molnar
parent 6a6a9d5fb9
commit fff9b6c7d2
1 changed files with 4 additions and 2 deletions
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6
Documentation/atomic_t.txt
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@ -81,9 +81,11 @@ Non-RMW ops:
The non-RMW ops are (typically) regular LOADs and STOREs and are canonically
implemented using READ_ONCE(), WRITE_ONCE(), smp_load_acquire() and
smp_store_release() respectively.
smp_store_release() respectively. Therefore, if you find yourself only using
the Non-RMW operations of atomic_t, you do not in fact need atomic_t at all
and are doing it wrong.
The one detail to this is that atomic_set{}() should be observable to the RMW
A subtle detail of atomic_set{}() is that it should be observable to the RMW
ops. That is:
C atomic-set