Re: [PATCH] rcutorture: Fix rcu_torture_pipe_update_one()/rcu_torture_writer() data race and concurrency bug

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

On 2024-03-06 21:43, Linus Torvalds wrote:
[...]
> 
> Honestly, this all makes me think that we'd be *much* better off
> showing the real "handoff" with smp_store_release() and
> smp_load_acquire().

We've done something similar in liburcu (userspace code) to allow
Thread Sanitizer to understand the happens-before relationships
within the RCU implementations and lock-free data structures.

Moving to load-acquire/store-release (C11 model in our case)
allowed us to provide enough happens-before relationship for
Thread Sanitizer to understand what is happening under the
hood in liburcu and perform relevant race detection of user
code.

As far as the WRITE_ONCE(x, READ_ONCE(x) + 1) pattern
is concerned, the only valid use-case I can think of is
split counters or RCU implementations where there is a
single updater doing the increment, and one or more
concurrent reader threads that need to snapshot a
consistent value with READ_ONCE().

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com