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From:   madhuparnabhowmik10@gmail.com
To:     pbonzini@redhat.com, cai@lca.pw
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        paulmck@kernel.org, joel@joelfernandes.org,
        linux-kernel-mentees@lists.linuxfoundation.org,
        frextrite@gmail.com,
        Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
Subject: [PATCH] kvm: Fix false-positive RCU list related warnings
Date:   Thu, 30 Apr 2020 23:06:08 +0530
Message-Id: <20200430173608.14663-1-madhuparnabhowmik10@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>

This patch fixes the following warning and other usage of
RCU list in eventfd.c

[29179.937976][T75781] WARNING: suspicious RCU usage
[29179.942789][T75781] 5.7.0-rc3-next-20200429 #1 Tainted: G           O L
[29179.949752][T75781] -----------------------------
[29179.954498][T75781] arch/x86/kvm/../../../virt/kvm/eventfd.c:472 RCU-list traversed in non-reader section!!

Pass srcu_read_lock_held() as cond to list_for_each_entry_rcu().

Reported-by: Qian Cai <cai@lca.pw>
Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
---
 virt/kvm/eventfd.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 67b6fc153e9c..a23787693127 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -77,7 +77,8 @@ irqfd_resampler_ack(struct kvm_irq_ack_notifier *kian)
 
 	idx = srcu_read_lock(&kvm->irq_srcu);
 
-	list_for_each_entry_rcu(irqfd, &resampler->list, resampler_link)
+	list_for_each_entry_rcu(irqfd, &resampler->list, resampler_link,
+				 srcu_read_lock_held(&kvm->irq_srcu))
 		eventfd_signal(irqfd->resamplefd, 1);
 
 	srcu_read_unlock(&kvm->irq_srcu, idx);
@@ -452,7 +453,7 @@ bool kvm_irq_has_notifier(struct kvm *kvm, unsigned irqchip, unsigned pin)
 	gsi = kvm_irq_map_chip_pin(kvm, irqchip, pin);
 	if (gsi != -1)
 		hlist_for_each_entry_rcu(kian, &kvm->irq_ack_notifier_list,
-					 link)
+					 link, srcu_read_lock_held(&kvm->irq_srcu))
 			if (kian->gsi == gsi) {
 				srcu_read_unlock(&kvm->irq_srcu, idx);
 				return true;
@@ -469,7 +470,7 @@ void kvm_notify_acked_gsi(struct kvm *kvm, int gsi)
 	struct kvm_irq_ack_notifier *kian;
 
 	hlist_for_each_entry_rcu(kian, &kvm->irq_ack_notifier_list,
-				 link)
+				 link, srcu_read_lock_held(&kvm->irq_srcu))
 		if (kian->gsi == gsi)
 			kian->irq_acked(kian);
 }
@@ -960,3 +961,4 @@ kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
 
 	return kvm_assign_ioeventfd(kvm, args);
 }
+
-- 
2.17.1