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SubjectRe: [PATCH v2] printk: Add console owner and waiter logic to load balance console writes
On Thu, 2 Nov 2017 13:06:05 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:


> + raw_spin_lock(&console_owner_lock);
> + waiter = console_waiter;
> + console_owner = NULL;
> + raw_spin_unlock(&console_owner_lock);
> +
> + /*
> + * If there is a waiter waiting for us, then pass the
> + * rest of the work load over to that waiter.
> + */
> + if (waiter)
> + break;

OK, the spin_unlock() wont let the load leak. Thus it is fine as is.


> + raw_spin_lock(&console_owner_lock);
> + owner = console_owner;
> + waiter = console_waiter;
> + if (!waiter && owner && owner != current) {

But Mathieu Desnoyers pointed out that usage of variables within a
spinlock may be an issue. Although, it shouldn't affect the code as is,
I think I'll add back READ/WRITE_ONCE() just to be on the safe side.

I may add the waiter = READ_ONCE(console_waiter) to the first one too,
more as documentation. It should cause any issues to add it.

-- Steve



> + console_waiter = true;
> + spin = true;
> + }
> + raw_spin_unlock(&console_owner_lock);

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