From: Davidlohr Bueso <dave@stgolabs.net>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: tglx@linutronix.de, peterz@infradead.org, maz@kernel.org,
bigeasy@linutronix.de, rostedt@goodmis.org,
torvalds@linux-foundation.org, will@kernel.org,
joel@joelfernandes.org, linux-kernel@vger.kernel.org,
kvm@vger.kernel.org, Davidlohr Bueso <dbueso@suse.de>
Subject: Re: [PATCH 4/5] rcuwait: Introduce rcuwait_active()
Date: Mon, 18 May 2020 09:37:00 -0700 [thread overview]
Message-ID: <20200518163700.4nn4csjlbpcixmsv@linux-p48b> (raw)
In-Reply-To: <57309494-58bf-a11e-e4ac-e669e6af22f2@redhat.com>
On Mon, 18 May 2020, Paolo Bonzini wrote:
>On 24/04/20 07:48, Davidlohr Bueso wrote:
>> +/*
>> + * Note: this provides no serialization and, just as with waitqueues,
>> + * requires care to estimate as to whether or not the wait is active.
>> + */
>> +static inline int rcuwait_active(struct rcuwait *w)
>> +{
>> + return !!rcu_dereference(w->task);
>> +}
>
>This needs to be changed to rcu_access_pointer:
>
>
>--------------- 8< -----------------
>From: Paolo Bonzini <pbonzini@redhat.com>
>Subject: [PATCH] rcuwait: avoid lockdep splats from rcuwait_active()
>
>rcuwait_active only returns whether w->task is not NULL. This is
>exactly one of the usecases that are mentioned in the documentation
>for rcu_access_pointer() where it is correct to bypass lockdep checks.
>
>This avoids a splat from kvm_vcpu_on_spin().
>
>Reported-by: Wanpeng Li <kernellwp@gmail.com>
>Cc: Peter Zijlstra <peterz@infradead.org>
>Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
next prev parent reply other threads:[~2020-05-18 16:42 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-24 5:48 [PATCH v4 0/5] kvm: Use rcuwait for vcpu blocking Davidlohr Bueso
2020-04-24 5:48 ` [PATCH 1/5] rcuwait: Fix stale wake call name in comment Davidlohr Bueso
2020-04-24 5:48 ` [PATCH 2/5] rcuwait: Let rcuwait_wake_up() return whether or not a task was awoken Davidlohr Bueso
2020-04-24 5:48 ` [PATCH 3/5] rcuwait: Introduce prepare_to and finish_rcuwait Davidlohr Bueso
2020-04-24 5:48 ` [PATCH 4/5] rcuwait: Introduce rcuwait_active() Davidlohr Bueso
2020-04-24 9:55 ` Peter Zijlstra
2020-05-18 10:33 ` Paolo Bonzini
2020-05-18 16:37 ` Davidlohr Bueso [this message]
2020-05-19 0:34 ` Wanpeng Li
2020-04-24 5:48 ` [PATCH 5/5] kvm: Replace vcpu->swait with rcuwait Davidlohr Bueso
2020-04-25 10:24 ` Paolo Bonzini
2020-04-25 22:30 ` Davidlohr Bueso
2020-05-18 8:51 ` Wanpeng Li
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