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Message-ID: <20181002090602.GB116695@gmail.com>
Date: Tue, 2 Oct 2018 11:06:02 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Waiman Long <longman@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Will Deacon <will.deacon@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] locking/lockdep: Eliminate redundant irqs check in
__lock_acquire()
* Waiman Long <longman@...hat.com> wrote:
> The static __lock_acquire() function has only two callers:
>
> 1) lock_acquire()
> 2) reacquire_held_locks()
>
> In lock_acquire(), raw_local_irq_save() is called before hand. So
> irqs must have been disabled. So the check
s/before hand/
/beforehand
s/irqs
/IRQs
>
> DEBUG_LOCKS_WARN_ON(!irqs_disabled())
>
> is kind of redundant in thise case. So move the above check
> to reacquire_held_locks() to eliminate redundant code in the
> lock_acquire path.
s/thise
/this
s/lock_acquire path
/lock_acquire() path
> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
> kernel/locking/lockdep.c | 15 +++++++--------
> 1 file changed, 7 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 8f9de7c..add0468 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -3192,6 +3192,10 @@ void lockdep_init_map(struct lockdep_map *lock, const char *name,
> /*
> * This gets called for every mutex_lock*()/spin_lock*() operation.
> * We maintain the dependency maps and validate the locking attempt:
> + *
> + * The callers must make sure that IRQs are disabled before calling it.
> + * otherwise we could get an interrupt which would want to take locks,
> + * which would end up in lockdep again.
Spelling nit: a comma after the first line, like it was in the original version:
> - /*
> - * Lockdep should run with IRQs disabled, otherwise we could
> - * get an interrupt which would want to take locks, which would
> - * end up in lockdep and have you got a head-ache already?
> - */
Thanks,
Ingo
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