Re: [PATCH 03/11] intel-iommu: Fix AB-BA lockdep report

[Shuah Khan <shuah.khan@hp.com>]

On Sun, 2011-12-04 at 13:54 -0500, Steven Rostedt wrote:
> From: Roland Dreier <roland@purestorage.com>
> 
> 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:

Did this patch not make it into stable releases other than 3.1. I
couldn't find it in any other stable tress prior to 3.1.

-- Shuah 
> 
>  - 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>
> ---
>  drivers/pci/intel-iommu.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
> index 8c2564d..bc05a51 100644
> --- a/drivers/pci/intel-iommu.c
> +++ b/drivers/pci/intel-iommu.c
> @@ -3569,6 +3569,8 @@ static void domain_remove_one_dev_info(struct dmar_domain *domain,
>  			found = 1;
>  	}
>  
> +	spin_unlock_irqrestore(&device_domain_lock, flags);
> +
>  	if (found == 0) {
>  		unsigned long tmp_flags;
>  		spin_lock_irqsave(&domain->iommu_lock, tmp_flags);
> @@ -3585,8 +3587,6 @@ static void domain_remove_one_dev_info(struct dmar_domain *domain,
>  			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)