linux-kernel - [PATCH AUTOSEL 5.5 47/75] iommu/vt-d: Silence RCU-list debugging warning in dmar_find

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Message-Id: <20200418140910.8280-47-sashal@kernel.org>
Date:   Sat, 18 Apr 2020 10:08:42 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Qian Cai <cai@....pw>, Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <jroedel@...e.de>,
        Sasha Levin <sashal@...nel.org>,
        iommu@...ts.linux-foundation.org
Subject: [PATCH AUTOSEL 5.5 47/75] iommu/vt-d: Silence RCU-list debugging warning in dmar_find_atsr()

From: Qian Cai <cai@....pw>

[ Upstream commit c6f4ebdeba4cff590594df931ff1ee610c426431 ]

dmar_find_atsr() calls list_for_each_entry_rcu() outside of an RCU read
side critical section but with dmar_global_lock held. Silence this
false positive.

 drivers/iommu/intel-iommu.c:4504 RCU-list traversed in non-reader section!!
 1 lock held by swapper/0/1:
 #0: ffffffff9755bee8 (dmar_global_lock){+.+.}, at: intel_iommu_init+0x1a6/0xe19

 Call Trace:
  dump_stack+0xa4/0xfe
  lockdep_rcu_suspicious+0xeb/0xf5
  dmar_find_atsr+0x1ab/0x1c0
  dmar_parse_one_atsr+0x64/0x220
  dmar_walk_remapping_entries+0x130/0x380
  dmar_table_init+0x166/0x243
  intel_iommu_init+0x1ab/0xe19
  pci_iommu_init+0x1a/0x44
  do_one_initcall+0xae/0x4d0
  kernel_init_freeable+0x412/0x4c5
  kernel_init+0x19/0x193

Signed-off-by: Qian Cai <cai@....pw>
Acked-by: Lu Baolu <baolu.lu@...ux.intel.com>
Signed-off-by: Joerg Roedel <jroedel@...e.de>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/iommu/intel-iommu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 87cd68a4e5eab..8e5d6732b48d2 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -4359,7 +4359,8 @@ static struct dmar_atsr_unit *dmar_find_atsr(struct acpi_dmar_atsr *atsr)
 	struct dmar_atsr_unit *atsru;
 	struct acpi_dmar_atsr *tmp;
 
-	list_for_each_entry_rcu(atsru, &dmar_atsr_units, list) {
+	list_for_each_entry_rcu(atsru, &dmar_atsr_units, list,
+				dmar_rcu_check()) {
 		tmp = (struct acpi_dmar_atsr *)atsru->hdr;
 		if (atsr->segment != tmp->segment)
 			continue;
-- 
2.20.1