On Mon, 2 Mar 2026 08:41:58 +0000
Chaitanya Kulkarni <[email protected]> wrote:

> I totally failed to understand why this bug is appearing right now
> than before.

I wonder if it is because it was never tested under PREEMPT_FULL, which
would be the only config that would trigger the warning, as
PREEMPT_VOLUNTARY has rcu_read_lock() not allow preemption.

Today, the default is now the new PREEMPT_LAZY and not PREEMPT_VOLUNTARY,
where it can preempt within rcu_read_lock(). It could be that this bug
existed since 2012 but was never triggered as most users use
PREEMPT_VOLUNTARY where it would not trigger. But if they used PREEMPT_FULL
back then, it may have.

Today we now use PREEMPT_LAZY where this does trigger.

-- Steve

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