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SubjectRe: [PATCH v4] printk: Add console owner and waiter logic to load balance console writes
On Fri, Nov 24, 2017 at 04:58:16PM +0100, Petr Mladek wrote:
> @@ -1797,13 +1797,6 @@ asmlinkage int vprintk_emit(int facility, int level,
> spin_release(&console_owner_dep_map, 1, _THIS_IP_);
> printk_safe_exit_irqrestore(flags);
>
> - /*
> - * The owner passed the console lock to us.
> - * Since we did not spin on console lock, annotate
> - * this as a trylock. Otherwise lockdep will
> - * complain.
> - */
> - mutex_acquire(&console_lock_dep_map, 0, 1, _THIS_IP_);

Hello Petr,

IMHO, it would get unbalanced if you only remove this mutex_acquire().

> console_unlock();
> printk_safe_enter_irqsave(flags);
> }
> @@ -2334,10 +2327,10 @@ void console_unlock(void)
> /* The waiter is now free to continue */
> spin_release(&console_owner_dep_map, 1, _THIS_IP_);
> /*
> - * Hand off console_lock to waiter. The waiter will perform
> - * the up(). After this, the waiter is the console_lock owner.
> + * Hand off console_lock to waiter. After this, the waiter
> + * is the console_lock owner.
> */
> - mutex_release(&console_lock_dep_map, 1, _THIS_IP_);

IMHO, this release() should be moved to somewhere properly.

> + lock_commit_crosslock((struct lockdep_map *)&console_lock_dep_map);
> printk_safe_exit_irqrestore(flags);
> /* Note, if waiter is set, logbuf_lock is not held */
> return;

However, now that cross-release was introduces, lockdep can be applied
to semaphore operations. Actually, I have a plan to do that. I think it
would be better to make semaphore tracked with lockdep and remove all
these manual acquire() and release() here. What do you think about it?

Thanks,
Byungchul

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