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From:   Qian Cai <cai@lca.pw>
To:     jroedel@suse.de
Cc:     baolu.lu@linux.intel.com, iommu@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, Qian Cai <cai@lca.pw>
Subject: [PATCH] iommu/vt-d: fix RCU-list bugs in intel_iommu_init
Date:   Thu,  5 Mar 2020 15:00:46 -0500
Message-Id: <1583438446-9959-1-git-send-email-cai@lca.pw>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

There are several places traverse RCU-list without holding any lock in
intel_iommu_init(). Fix them by acquiring dmar_global_lock.

 WARNING: suspicious RCU usage
 -----------------------------
 drivers/iommu/intel-iommu.c:5216 RCU-list traversed in non-reader section!!

 other info that might help us debug this:

 rcu_scheduler_active = 2, debug_locks = 1
 no locks held by swapper/0/1.

 Call Trace:
  dump_stack+0xa0/0xea
  lockdep_rcu_suspicious+0x102/0x10b
  intel_iommu_init+0x947/0xb13
  pci_iommu_init+0x26/0x62
  do_one_initcall+0xfe/0x500
  kernel_init_freeable+0x45a/0x4f8
  kernel_init+0x11/0x139
  ret_from_fork+0x3a/0x50
 DMAR: Intel(R) Virtualization Technology for Directed I/O

Fixes: d8190dc63886 ("iommu/vt-d: Enable DMA remapping after rmrr mapped")
Signed-off-by: Qian Cai <cai@lca.pw>
---
 drivers/iommu/intel-iommu.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 6fa6de2b6ad5..bc138ceb07bc 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -5193,6 +5193,7 @@ int __init intel_iommu_init(void)
 
 	init_iommu_pm_ops();
 
+	down_read(&dmar_global_lock);
 	for_each_active_iommu(iommu, drhd) {
 		iommu_device_sysfs_add(&iommu->iommu, NULL,
 				       intel_iommu_groups,
@@ -5200,6 +5201,7 @@ int __init intel_iommu_init(void)
 		iommu_device_set_ops(&iommu->iommu, &intel_iommu_ops);
 		iommu_device_register(&iommu->iommu);
 	}
+	up_read(&dmar_global_lock);
 
 	bus_set_iommu(&pci_bus_type, &intel_iommu_ops);
 	if (si_domain && !hw_pass_through)
@@ -5210,7 +5212,6 @@ int __init intel_iommu_init(void)
 	down_read(&dmar_global_lock);
 	if (probe_acpi_namespace_devices())
 		pr_warn("ACPI name space devices didn't probe correctly\n");
-	up_read(&dmar_global_lock);
 
 	/* Finally, we enable the DMA remapping hardware. */
 	for_each_iommu(iommu, drhd) {
@@ -5219,6 +5220,8 @@ int __init intel_iommu_init(void)
 
 		iommu_disable_protect_mem_regions(iommu);
 	}
+	up_read(&dmar_global_lock);
+
 	pr_info("Intel(R) Virtualization Technology for Directed I/O\n");
 
 	intel_iommu_enabled = 1;
-- 
1.8.3.1