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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Clark Williams <williams@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Steven Rostedt <rostedt@goodmis.org>,
	Dmitry Vyukov <dvyukov@google.com>,
	Andrey Konovalov <andreyknvl@gmail.com>,
	kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH PREEMPT_RT] kcov:  fix locking splat from kcov_remote_start()
Date: Tue, 10 Aug 2021 11:50:32 +0200	[thread overview]
Message-ID: <20210810095032.epdhivjifjlmbhp5@linutronix.de> (raw)
In-Reply-To: <20210809155909.333073de@theseus.lan>

On 2021-08-09 15:59:09 [-0500], Clark Williams wrote:
> Saw the following splat on 5.14-rc4-rt5 with:
…
> Change kcov_remote_lock from regular spinlock_t to raw_spinlock_t so that
> we don't get "sleeping function called from invalid context" on PREEMPT_RT kernel.

I'm not entirely happy with that:
- kcov_remote_start() decouples spin_lock_irq() and does local_irq_save()
  + spin_lock() which shouldn't be done as per
      Documentation/locking/locktypes.rst
  I would prefer to see the local_irq_save() replaced by
  local_lock_irqsave() so we get a context on what is going on.

- kcov_remote_reset() has a kfree() with that irq-off lock acquired.

- kcov_remote_add() has a kmalloc() and is invoked with that irq-off
  lock acquired.

- kcov_remote_area_put() uses INIT_LIST_HEAD() for no reason (just
  happen to notice).

- kcov_remote_stop() does local_irq_save() + spin_lock(&kcov->lock);.
  This should also create a splat.

- With lock kcov_remote_lock acquired there is a possible
  hash_for_each_safe() and list_for_each() iteration. I don't know what
  the limits are here but with a raw_spinlock_t it will contribute to
  the maximal latency. 

> Signed-off-by: Clark Williams <williams@redhat.com>

Sebastian

  parent reply	other threads:[~2021-08-10  9:50 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-09 20:59 [PATCH PREEMPT_RT] kcov: fix locking splat from kcov_remote_start() Clark Williams
2021-08-10  9:42 ` Marco Elver
2021-08-10  9:50 ` Sebastian Andrzej Siewior [this message]
2021-08-10 19:14   ` Steven Rostedt
2021-08-10 20:38   ` Thomas Gleixner
2021-08-11  9:00     ` Sebastian Andrzej Siewior
2021-08-11 12:25       ` Thomas Gleixner

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