linux-kernel - [PATCH] iommu: dmar: Fix RCU list debugging warnings

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Date:   Sat, 22 Feb 2020 22:33:33 +0530
From:   Amol Grover <frextrite@...il.com>
To:     Allison Randal <allison@...utok.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>, Qian Cai <cai@....pw>,
        Deepa Dinamani <deepa.kernel@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        Joel Fernandes <joel@...lfernandes.org>,
        Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Amol Grover <frextrite@...il.com>
Subject: [PATCH] iommu: dmar: Fix RCU list debugging warnings

dmar_drhd_units is traversed using list_for_each_entry_rcu()
outside of an RCU read side critical section but under the
protection of dmar_global_lock. Hence add corresponding lockdep
expression to silence the following false-positive warnings:

[    1.603975] =============================
[    1.603976] WARNING: suspicious RCU usage
[    1.603977] 5.5.4-stable #17 Not tainted
[    1.603978] -----------------------------
[    1.603980] drivers/iommu/intel-iommu.c:4769 RCU-list traversed in non-reader section!!

[    1.603869] =============================
[    1.603870] WARNING: suspicious RCU usage
[    1.603872] 5.5.4-stable #17 Not tainted
[    1.603874] -----------------------------
[    1.603875] drivers/iommu/dmar.c:293 RCU-list traversed in non-reader section!!

Tested-by: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
Signed-off-by: Amol Grover <frextrite@...il.com>
---
 include/linux/dmar.h | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/include/linux/dmar.h b/include/linux/dmar.h
index f64ca27dc210..712be8bc6a7c 100644
--- a/include/linux/dmar.h
+++ b/include/linux/dmar.h
@@ -69,8 +69,9 @@ struct dmar_pci_notify_info {
 extern struct rw_semaphore dmar_global_lock;
 extern struct list_head dmar_drhd_units;
 
-#define for_each_drhd_unit(drhd) \
-	list_for_each_entry_rcu(drhd, &dmar_drhd_units, list)
+#define for_each_drhd_unit(drhd)					\
+	list_for_each_entry_rcu(drhd, &dmar_drhd_units, list,		\
+				dmar_rcu_check())
 
 #define for_each_active_drhd_unit(drhd)					\
 	list_for_each_entry_rcu(drhd, &dmar_drhd_units, list)		\
@@ -81,7 +82,8 @@ extern struct list_head dmar_drhd_units;
 		if (i=drhd->iommu, drhd->ignored) {} else
 
 #define for_each_iommu(i, drhd)						\
-	list_for_each_entry_rcu(drhd, &dmar_drhd_units, list)		\
+	list_for_each_entry_rcu(drhd, &dmar_drhd_units, list,		\
+				dmar_rcu_check())			\
 		if (i=drhd->iommu, 0) {} else 
 
 static inline bool dmar_rcu_check(void)
-- 
2.24.1