--- /dev/null
+From 3e7abe2556b583e87dabda3e0e6178a67b20d06f Mon Sep 17 00:00:00 2001
+From: Roland Dreier <roland@purestorage.com>
+Date: Wed, 20 Jul 2011 06:22:21 -0700
+Subject: intel-iommu: Fix AB-BA lockdep report
+
+From: Roland Dreier <roland@purestorage.com>
+
+commit 3e7abe2556b583e87dabda3e0e6178a67b20d06f upstream.
+
+When unbinding a device so that I could pass it through to a KVM VM, I
+got the lockdep report below. It looks like a legitimate lock
+ordering problem:
+
+ - domain_context_mapping_one() takes iommu->lock and calls
+ iommu_support_dev_iotlb(), which takes device_domain_lock (inside
+ iommu->lock).
+
+ - domain_remove_one_dev_info() starts by taking device_domain_lock
+ then takes iommu->lock inside it (near the end of the function).
+
+So this is the classic AB-BA deadlock. It looks like a safe fix is to
+simply release device_domain_lock a bit earlier, since as far as I can
+tell, it doesn't protect any of the stuff accessed at the end of
+domain_remove_one_dev_info() anyway.
+
+BTW, the use of device_domain_lock looks a bit unsafe to me... it's
+at least not obvious to me why we aren't vulnerable to the race below:
+
+ iommu_support_dev_iotlb()
+ domain_remove_dev_info()
+
+ lock device_domain_lock
+ find info
+ unlock device_domain_lock
+
+ lock device_domain_lock
+ find same info
+ unlock device_domain_lock
+
+ free_devinfo_mem(info)
+
+ do stuff with info after it's free
+
+However I don't understand the locking here well enough to know if
+this is a real problem, let alone what the best fix is.
+
+Anyway here's the full lockdep output that prompted all of this:
+
+ =======================================================
+ [ INFO: possible circular locking dependency detected ]
+ 2.6.39.1+ #1
+ -------------------------------------------------------
+ bash/13954 is trying to acquire lock:
+ (&(&iommu->lock)->rlock){......}, at: [<ffffffff812f6421>] domain_remove_one_dev_info+0x121/0x230
+
+ but task is already holding lock:
+ (device_domain_lock){-.-...}, at: [<ffffffff812f6508>] domain_remove_one_dev_info+0x208/0x230
+
+ which lock already depends on the new lock.
+
+ the existing dependency chain (in reverse order) is:
+
+ -> #1 (device_domain_lock){-.-...}:
+ [<ffffffff8109ca9d>] lock_acquire+0x9d/0x130
+ [<ffffffff81571475>] _raw_spin_lock_irqsave+0x55/0xa0
+ [<ffffffff812f8350>] domain_context_mapping_one+0x600/0x750
+ [<ffffffff812f84df>] domain_context_mapping+0x3f/0x120
+ [<ffffffff812f9175>] iommu_prepare_identity_map+0x1c5/0x1e0
+ [<ffffffff81ccf1ca>] intel_iommu_init+0x88e/0xb5e
+ [<ffffffff81cab204>] pci_iommu_init+0x16/0x41
+ [<ffffffff81002165>] do_one_initcall+0x45/0x190
+ [<ffffffff81ca3d3f>] kernel_init+0xe3/0x168
+ [<ffffffff8157ac24>] kernel_thread_helper+0x4/0x10
+
+ -> #0 (&(&iommu->lock)->rlock){......}:
+ [<ffffffff8109bf3e>] __lock_acquire+0x195e/0x1e10
+ [<ffffffff8109ca9d>] lock_acquire+0x9d/0x130
+ [<ffffffff81571475>] _raw_spin_lock_irqsave+0x55/0xa0
+ [<ffffffff812f6421>] domain_remove_one_dev_info+0x121/0x230
+ [<ffffffff812f8b42>] device_notifier+0x72/0x90
+ [<ffffffff8157555c>] notifier_call_chain+0x8c/0xc0
+ [<ffffffff81089768>] __blocking_notifier_call_chain+0x78/0xb0
+ [<ffffffff810897b6>] blocking_notifier_call_chain+0x16/0x20
+ [<ffffffff81373a5c>] __device_release_driver+0xbc/0xe0
+ [<ffffffff81373ccf>] device_release_driver+0x2f/0x50
+ [<ffffffff81372ee3>] driver_unbind+0xa3/0xc0
+ [<ffffffff813724ac>] drv_attr_store+0x2c/0x30
+ [<ffffffff811e4506>] sysfs_write_file+0xe6/0x170
+ [<ffffffff8117569e>] vfs_write+0xce/0x190
+ [<ffffffff811759e4>] sys_write+0x54/0xa0
+ [<ffffffff81579a82>] system_call_fastpath+0x16/0x1b
+
+ other info that might help us debug this:
+
+ 6 locks held by bash/13954:
+ #0: (&buffer->mutex){+.+.+.}, at: [<ffffffff811e4464>] sysfs_write_file+0x44/0x170
+ #1: (s_active#3){++++.+}, at: [<ffffffff811e44ed>] sysfs_write_file+0xcd/0x170
+ #2: (&__lockdep_no_validate__){+.+.+.}, at: [<ffffffff81372edb>] driver_unbind+0x9b/0xc0
+ #3: (&__lockdep_no_validate__){+.+.+.}, at: [<ffffffff81373cc7>] device_release_driver+0x27/0x50
+ #4: (&(&priv->bus_notifier)->rwsem){.+.+.+}, at: [<ffffffff8108974f>] __blocking_notifier_call_chain+0x5f/0xb0
+ #5: (device_domain_lock){-.-...}, at: [<ffffffff812f6508>] domain_remove_one_dev_info+0x208/0x230
+
+ stack backtrace:
+ Pid: 13954, comm: bash Not tainted 2.6.39.1+ #1
+ Call Trace:
+ [<ffffffff810993a7>] print_circular_bug+0xf7/0x100
+ [<ffffffff8109bf3e>] __lock_acquire+0x195e/0x1e10
+ [<ffffffff810972bd>] ? trace_hardirqs_off+0xd/0x10
+ [<ffffffff8109d57d>] ? trace_hardirqs_on_caller+0x13d/0x180
+ [<ffffffff8109ca9d>] lock_acquire+0x9d/0x130
+ [<ffffffff812f6421>] ? domain_remove_one_dev_info+0x121/0x230
+ [<ffffffff81571475>] _raw_spin_lock_irqsave+0x55/0xa0
+ [<ffffffff812f6421>] ? domain_remove_one_dev_info+0x121/0x230
+ [<ffffffff810972bd>] ? trace_hardirqs_off+0xd/0x10
+ [<ffffffff812f6421>] domain_remove_one_dev_info+0x121/0x230
+ [<ffffffff812f8b42>] device_notifier+0x72/0x90
+ [<ffffffff8157555c>] notifier_call_chain+0x8c/0xc0
+ [<ffffffff81089768>] __blocking_notifier_call_chain+0x78/0xb0
+ [<ffffffff810897b6>] blocking_notifier_call_chain+0x16/0x20
+ [<ffffffff81373a5c>] __device_release_driver+0xbc/0xe0
+ [<ffffffff81373ccf>] device_release_driver+0x2f/0x50
+ [<ffffffff81372ee3>] driver_unbind+0xa3/0xc0
+ [<ffffffff813724ac>] drv_attr_store+0x2c/0x30
+ [<ffffffff811e4506>] sysfs_write_file+0xe6/0x170
+ [<ffffffff8117569e>] vfs_write+0xce/0x190
+ [<ffffffff811759e4>] sys_write+0x54/0xa0
+ [<ffffffff81579a82>] system_call_fastpath+0x16/0x1b
+
+Signed-off-by: Roland Dreier <roland@purestorage.com>
+Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
+Cc: Steven Rostedt <rostedt@goodmis.org>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ drivers/pci/intel-iommu.c | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+--- a/drivers/pci/intel-iommu.c
++++ b/drivers/pci/intel-iommu.c
+@@ -3573,6 +3573,8 @@ static void domain_remove_one_dev_info(s
+ found = 1;
+ }
+
++ spin_unlock_irqrestore(&device_domain_lock, flags);
++
+ if (found == 0) {
+ unsigned long tmp_flags;
+ spin_lock_irqsave(&domain->iommu_lock, tmp_flags);
+@@ -3589,8 +3591,6 @@ static void domain_remove_one_dev_info(s
+ spin_unlock_irqrestore(&iommu->lock, tmp_flags);
+ }
+ }
+-
+- spin_unlock_irqrestore(&device_domain_lock, flags);
+ }
+
+ static void vm_domain_remove_all_dev_info(struct dmar_domain *domain)