linux-kernel - [PATCH] kvm: Fix false positive RCU usage warning

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Message-Id: <20200428155249.19990-1-madhuparnabhowmik10@gmail.com>
Date:   Tue, 28 Apr 2020 21:22:49 +0530
From:   madhuparnabhowmik10@...il.com
To:     sean.j.christopherson@...el.com, wanpengli@...cent.com,
        jmattson@...gle.com, tglx@...utronix.de, bp@...en8.de,
        mingo@...hat.com
Cc:     cai@....pw, paulmck@...nel.org, joel@...lfernandes.org,
        frextrite@...il.com, x86@...nel.org, kvm@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-kernel@...r.kernel.org,
        Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
Subject: [PATCH] kvm: Fix false positive RCU usage warning

From: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>

Fix the following false positive warnings:

[ 9403.765413][T61744] =============================
[ 9403.786541][T61744] WARNING: suspicious RCU usage
[ 9403.807865][T61744] 5.7.0-rc1-next-20200417 #4 Tainted: G             L
[ 9403.838945][T61744] -----------------------------
[ 9403.860099][T61744] arch/x86/kvm/mmu/page_track.c:257 RCU-list traversed in non-reader section!!

and

[ 9405.859252][T61751] =============================
[ 9405.859258][T61751] WARNING: suspicious RCU usage
[ 9405.880867][T61755] -----------------------------
[ 9405.911936][T61751] 5.7.0-rc1-next-20200417 #4 Tainted: G             L
[ 9405.911942][T61751] -----------------------------
[ 9405.911950][T61751] arch/x86/kvm/mmu/page_track.c:232 RCU-list traversed in non-reader section!!

Since srcu read lock is held, these are false positive warnings.
Therefore, pass condition srcu_read_lock_held() to
list_for_each_entry_rcu().

Reported-by: kernel test robot <lkp@...el.com>
Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
---
 arch/x86/kvm/mmu/page_track.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c
index ddc1ec3bdacd..1ad79c7aa05b 100644
--- a/arch/x86/kvm/mmu/page_track.c
+++ b/arch/x86/kvm/mmu/page_track.c
@@ -229,7 +229,8 @@ void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
 		return;
 
 	idx = srcu_read_lock(&head->track_srcu);
-	hlist_for_each_entry_rcu(n, &head->track_notifier_list, node)
+	hlist_for_each_entry_rcu(n, &head->track_notifier_list, node,
+				srcu_read_lock_held(&head->track_srcu))
 		if (n->track_write)
 			n->track_write(vcpu, gpa, new, bytes, n);
 	srcu_read_unlock(&head->track_srcu, idx);
@@ -254,7 +255,8 @@ void kvm_page_track_flush_slot(struct kvm *kvm, struct kvm_memory_slot *slot)
 		return;
 
 	idx = srcu_read_lock(&head->track_srcu);
-	hlist_for_each_entry_rcu(n, &head->track_notifier_list, node)
+	hlist_for_each_entry_rcu(n, &head->track_notifier_list, node,
+				srcu_read_lock_held(&head->track_srcu))
 		if (n->track_flush_slot)
 			n->track_flush_slot(kvm, slot, n);
 	srcu_read_unlock(&head->track_srcu, idx);
-- 
2.17.1