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Date: Tue, 10 Aug 2021 11:50:32 +0200 From: Sebastian Andrzej Siewior <bigeasy@...utronix.de> To: Clark Williams <williams@...hat.com> Cc: Thomas Gleixner <tglx@...utronix.de>, Steven Rostedt <rostedt@...dmis.org>, Dmitry Vyukov <dvyukov@...gle.com>, Andrey Konovalov <andreyknvl@...il.com>, kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org Subject: Re: [PATCH PREEMPT_RT] kcov: fix locking splat from kcov_remote_start() 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@...hat.com> Sebastian
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