[PATCH v3] iommu/arm-smmu: avoid calling request_irq in atomic context

[PATCH v3] iommu/arm-smmu: avoid calling request_irq in atomic context

[Mitchel Humpherys]

request_irq shouldn't be called from atomic context since it might
sleep, but we're calling it with a spinlock held, resulting in:

    [    9.172202] BUG: sleeping function called from invalid context at kernel/mm/slub.c:926
    [    9.182989] in_atomic(): 1, irqs_disabled(): 128, pid: 1, name: swapper/0
    [    9.189762] CPU: 1 PID: 1 Comm: swapper/0 Tainted: G        W    3.10.40-gbc1b510b-38437-g55831d3bd9-dirty #97
    [    9.199757] [<c020c448>] (unwind_backtrace+0x0/0x11c) from [<c02097d0>] (show_stack+0x10/0x14)
    [    9.208346] [<c02097d0>] (show_stack+0x10/0x14) from [<c0301d74>] (kmem_cache_alloc_trace+0x3c/0x210)
    [    9.217543] [<c0301d74>] (kmem_cache_alloc_trace+0x3c/0x210) from [<c0276a48>] (request_threaded_irq+0x88/0x11c)
    [    9.227702] [<c0276a48>] (request_threaded_irq+0x88/0x11c) from [<c0931ca4>] (arm_smmu_attach_dev+0x188/0x858)
    [    9.237686] [<c0931ca4>] (arm_smmu_attach_dev+0x188/0x858) from [<c0212cd8>] (arm_iommu_attach_device+0x18/0xd0)
    [    9.247837] [<c0212cd8>] (arm_iommu_attach_device+0x18/0xd0) from [<c093314c>] (arm_smmu_test_probe+0x68/0xd4)
    [    9.257823] [<c093314c>] (arm_smmu_test_probe+0x68/0xd4) from [<c05aadd0>] (driver_probe_device+0x12c/0x330)
    [    9.267629] [<c05aadd0>] (driver_probe_device+0x12c/0x330) from [<c05ab080>] (__driver_attach+0x68/0x8c)
    [    9.277090] [<c05ab080>] (__driver_attach+0x68/0x8c) from [<c05a92d4>] (bus_for_each_dev+0x70/0x84)
    [    9.286118] [<c05a92d4>] (bus_for_each_dev+0x70/0x84) from [<c05aa3b0>] (bus_add_driver+0x100/0x244)
    [    9.295233] [<c05aa3b0>] (bus_add_driver+0x100/0x244) from [<c05ab5d0>] (driver_register+0x9c/0x124)
    [    9.304347] [<c05ab5d0>] (driver_register+0x9c/0x124) from [<c0933088>] (arm_smmu_test_init+0x14/0x38)
    [    9.313635] [<c0933088>] (arm_smmu_test_init+0x14/0x38) from [<c0200618>] (do_one_initcall+0xb8/0x160)
    [    9.322926] [<c0200618>] (do_one_initcall+0xb8/0x160) from [<c1200b7c>] (kernel_init_freeable+0x108/0x1cc)
    [    9.332564] [<c1200b7c>] (kernel_init_freeable+0x108/0x1cc) from [<c0b924b0>] (kernel_init+0xc/0xe4)
    [    9.341675] [<c0b924b0>] (kernel_init+0xc/0xe4) from [<c0205e38>] (ret_from_fork+0x14/0x3c)

Fix this by moving the request_irq out of the critical section. This
should be okay since smmu_domain->smmu is still being protected by the
critical section. Also, we still don't program the Stream Match Register
until after registering our interrupt handler so we shouldn't be missing
any interrupts.

Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>
---
Changelog:

  - v3: rework irq request code to avoid requesting the irq every
        time a master is added to the domain
  - v2: return error code from request_irq on failure
---
 drivers/iommu/arm-smmu.c | 73 +++++++++++++++++++++++++++---------------------
 1 file changed, 41 insertions(+), 32 deletions(-)

diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index f3f66416e2..572f5579d3 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -868,7 +868,7 @@ static void arm_smmu_init_context_bank(struct arm_smmu_domain *smmu_domain)
 static int arm_smmu_init_domain_context(struct iommu_domain *domain,
 					struct arm_smmu_device *smmu)
 {
-	int irq, ret, start;
+	int ret, start;
 	struct arm_smmu_domain *smmu_domain = domain->priv;
 	struct arm_smmu_cfg *cfg = &smmu_domain->cfg;
 
@@ -900,23 +900,9 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
 		cfg->irptndx = cfg->cbndx;
 	}
 
-	irq = smmu->irqs[smmu->num_global_irqs + cfg->irptndx];
-	ret = request_irq(irq, arm_smmu_context_fault, IRQF_SHARED,
-			  "arm-smmu-context-fault", domain);
-	if (IS_ERR_VALUE(ret)) {
-		dev_err(smmu->dev, "failed to request context IRQ %d (%u)\n",
-			cfg->irptndx, irq);
-		cfg->irptndx = INVALID_IRPTNDX;
-		goto out_free_context;
-	}
-
-	smmu_domain->smmu = smmu;
+	ACCESS_ONCE(smmu_domain->smmu) = smmu;
 	arm_smmu_init_context_bank(smmu_domain);
 	return 0;
-
-out_free_context:
-	__arm_smmu_free_bitmap(smmu->context_map, cfg->cbndx);
-	return ret;
 }
 
 static void arm_smmu_destroy_domain_context(struct iommu_domain *domain)
@@ -1172,10 +1158,11 @@ static void arm_smmu_domain_remove_master(struct arm_smmu_domain *smmu_domain,
 
 static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
 {
-	int ret = -EINVAL;
+	int irq, ret;
 	struct arm_smmu_domain *smmu_domain = domain->priv;
-	struct arm_smmu_device *smmu;
-	struct arm_smmu_master_cfg *cfg;
+	struct arm_smmu_device *smmu, *dom_smmu;
+	struct arm_smmu_master_cfg *master_cfg;
+	struct arm_smmu_cfg *cfg = &smmu_domain->cfg;
 	unsigned long flags;
 
 	smmu = dev_get_master_dev(dev)->archdata.iommu;
@@ -1184,35 +1171,57 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
 		return -ENXIO;
 	}
 
+	dom_smmu = ACCESS_ONCE(smmu_domain->smmu);
+
 	/*
 	 * Sanity check the domain. We don't support domains across
 	 * different SMMUs.
 	 */
-	spin_lock_irqsave(&smmu_domain->lock, flags);
-	if (!smmu_domain->smmu) {
+	if (!dom_smmu) {
+		spin_lock_irqsave(&smmu_domain->lock, flags);
+		/*
+		 * make sure we're not racing with someone who might
+		 * have just attached and init'd the domain context
+		 */
+		dom_smmu = smmu_domain->smmu;
+		if (dom_smmu) {
+			spin_unlock_irqrestore(&smmu_domain->lock, flags);
+			goto have_dom_smmu;
+		}
 		/* Now that we have a master, we can finalise the domain */
 		ret = arm_smmu_init_domain_context(domain, smmu);
+		spin_unlock_irqrestore(&smmu_domain->lock, flags);
 		if (IS_ERR_VALUE(ret))
-			goto err_unlock;
-	} else if (smmu_domain->smmu != smmu) {
+			return ret;
+		dom_smmu = smmu_domain->smmu;
+
+		irq = smmu->irqs[smmu->num_global_irqs + cfg->irptndx];
+		ret = request_irq(irq, arm_smmu_context_fault, IRQF_SHARED,
+				"arm-smmu-context-fault", domain);
+		if (IS_ERR_VALUE(ret)) {
+			dev_err(smmu->dev, "failed to request context IRQ %d (%u)\n",
+				cfg->irptndx, irq);
+			cfg->irptndx = INVALID_IRPTNDX;
+			return ret;
+		}
+	}
+
+have_dom_smmu:
+
+	if (dom_smmu != smmu) {
 		dev_err(dev,
 			"cannot attach to SMMU %s whilst already attached to domain on SMMU %s\n",
 			dev_name(smmu_domain->smmu->dev),
 			dev_name(smmu->dev));
-		goto err_unlock;
+		return -EINVAL;
 	}
-	spin_unlock_irqrestore(&smmu_domain->lock, flags);
 
 	/* Looks ok, so add the device to the domain */
-	cfg = find_smmu_master_cfg(smmu_domain->smmu, dev);
-	if (!cfg)
+	master_cfg = find_smmu_master_cfg(smmu_domain->smmu, dev);
+	if (!master_cfg)
 		return -ENODEV;
 
-	return arm_smmu_domain_add_master(smmu_domain, cfg);
-
-err_unlock:
-	spin_unlock_irqrestore(&smmu_domain->lock, flags);
-	return ret;
+	return arm_smmu_domain_add_master(smmu_domain, master_cfg);
 }
 
 static void arm_smmu_detach_dev(struct iommu_domain *domain, struct device *dev)
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
hosted by The Linux Foundation

[PATCH v3] iommu/arm-smmu: avoid calling request_irq in atomic context

[Will Deacon]

Hey Mitch,

On Tue, Jul 29, 2014 at 07:11:15PM +0100, Mitchel Humpherys wrote:
> request_irq shouldn't be called from atomic context since it might
> sleep, but we're calling it with a spinlock held, resulting in:
> 
>     [    9.172202] BUG: sleeping function called from invalid context at kernel/mm/slub.c:926
>     [    9.182989] in_atomic(): 1, irqs_disabled(): 128, pid: 1, name: swapper/0
>     [    9.189762] CPU: 1 PID: 1 Comm: swapper/0 Tainted: G        W    3.10.40-gbc1b510b-38437-g55831d3bd9-dirty #97
>     [    9.199757] [<c020c448>] (unwind_backtrace+0x0/0x11c) from [<c02097d0>] (show_stack+0x10/0x14)
>     [    9.208346] [<c02097d0>] (show_stack+0x10/0x14) from [<c0301d74>] (kmem_cache_alloc_trace+0x3c/0x210)
>     [    9.217543] [<c0301d74>] (kmem_cache_alloc_trace+0x3c/0x210) from [<c0276a48>] (request_threaded_irq+0x88/0x11c)
>     [    9.227702] [<c0276a48>] (request_threaded_irq+0x88/0x11c) from [<c0931ca4>] (arm_smmu_attach_dev+0x188/0x858)
>     [    9.237686] [<c0931ca4>] (arm_smmu_attach_dev+0x188/0x858) from [<c0212cd8>] (arm_iommu_attach_device+0x18/0xd0)
>     [    9.247837] [<c0212cd8>] (arm_iommu_attach_device+0x18/0xd0) from [<c093314c>] (arm_smmu_test_probe+0x68/0xd4)
>     [    9.257823] [<c093314c>] (arm_smmu_test_probe+0x68/0xd4) from [<c05aadd0>] (driver_probe_device+0x12c/0x330)
>     [    9.267629] [<c05aadd0>] (driver_probe_device+0x12c/0x330) from [<c05ab080>] (__driver_attach+0x68/0x8c)
>     [    9.277090] [<c05ab080>] (__driver_attach+0x68/0x8c) from [<c05a92d4>] (bus_for_each_dev+0x70/0x84)
>     [    9.286118] [<c05a92d4>] (bus_for_each_dev+0x70/0x84) from [<c05aa3b0>] (bus_add_driver+0x100/0x244)
>     [    9.295233] [<c05aa3b0>] (bus_add_driver+0x100/0x244) from [<c05ab5d0>] (driver_register+0x9c/0x124)
>     [    9.304347] [<c05ab5d0>] (driver_register+0x9c/0x124) from [<c0933088>] (arm_smmu_test_init+0x14/0x38)
>     [    9.313635] [<c0933088>] (arm_smmu_test_init+0x14/0x38) from [<c0200618>] (do_one_initcall+0xb8/0x160)
>     [    9.322926] [<c0200618>] (do_one_initcall+0xb8/0x160) from [<c1200b7c>] (kernel_init_freeable+0x108/0x1cc)
>     [    9.332564] [<c1200b7c>] (kernel_init_freeable+0x108/0x1cc) from [<c0b924b0>] (kernel_init+0xc/0xe4)
>     [    9.341675] [<c0b924b0>] (kernel_init+0xc/0xe4) from [<c0205e38>] (ret_from_fork+0x14/0x3c)
> 
> Fix this by moving the request_irq out of the critical section. This
> should be okay since smmu_domain->smmu is still being protected by the
> critical section. Also, we still don't program the Stream Match Register
> until after registering our interrupt handler so we shouldn't be missing
> any interrupts.
> 
> Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>
> ---
> Changelog:
> 
>   - v3: rework irq request code to avoid requesting the irq every
>         time a master is added to the domain
>   - v2: return error code from request_irq on failure
> ---
>  drivers/iommu/arm-smmu.c | 73 +++++++++++++++++++++++++++---------------------
>  1 file changed, 41 insertions(+), 32 deletions(-)

I think this is correct, but we can do some cleanup now that you've moved
all the locking into the conditional. Messy diff below, which would be much
nicer sqaushed into your patch.

What do you reckon?

Will

--->8

diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index 572f5579d38b..e33df1a676ec 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -868,10 +868,15 @@ static void arm_smmu_init_context_bank(struct arm_smmu_domain *smmu_domain)
 static int arm_smmu_init_domain_context(struct iommu_domain *domain,
 					struct arm_smmu_device *smmu)
 {
-	int ret, start;
+	int irq, start, ret = 0;
+	unsigned long flags;
 	struct arm_smmu_domain *smmu_domain = domain->priv;
 	struct arm_smmu_cfg *cfg = &smmu_domain->cfg;
 
+	spin_lock_irqsave(&smmu_domain->lock, flags);
+	if (smmu_domain->smmu)
+		goto out_unlock;
+
 	if (smmu->features & ARM_SMMU_FEAT_TRANS_NESTED) {
 		/*
 		 * We will likely want to change this if/when KVM gets
@@ -890,7 +895,7 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
 	ret = __arm_smmu_alloc_bitmap(smmu->context_map, start,
 				      smmu->num_context_banks);
 	if (IS_ERR_VALUE(ret))
-		return ret;
+		goto out_unlock;
 
 	cfg->cbndx = ret;
 	if (smmu->version == 1) {
@@ -902,7 +907,22 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
 
 	ACCESS_ONCE(smmu_domain->smmu) = smmu;
 	arm_smmu_init_context_bank(smmu_domain);
+	spin_unlock_irqrestore(&smmu_domain->lock, flags);
+
+	irq = smmu->irqs[smmu->num_global_irqs + cfg->irptndx];
+	ret = request_irq(irq, arm_smmu_context_fault, IRQF_SHARED,
+			  "arm-smmu-context-fault", smmu_domain);
+	if (IS_ERR_VALUE(ret)) {
+		dev_err(smmu->dev, "failed to request context IRQ %d (%u)\n",
+			cfg->irptndx, irq);
+		cfg->irptndx = INVALID_IRPTNDX;
+	}
+
 	return 0;
+
+out_unlock:
+	spin_unlock_irqrestore(&smmu_domain->lock, flags);
+	return ret;
 }
 
 static void arm_smmu_destroy_domain_context(struct iommu_domain *domain)
@@ -1158,12 +1178,10 @@ static void arm_smmu_domain_remove_master(struct arm_smmu_domain *smmu_domain,
 
 static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
 {
-	int irq, ret;
+	int ret;
 	struct arm_smmu_domain *smmu_domain = domain->priv;
 	struct arm_smmu_device *smmu, *dom_smmu;
-	struct arm_smmu_master_cfg *master_cfg;
-	struct arm_smmu_cfg *cfg = &smmu_domain->cfg;
-	unsigned long flags;
+	struct arm_smmu_master_cfg *cfg;
 
 	smmu = dev_get_master_dev(dev)->archdata.iommu;
 	if (!smmu) {
@@ -1171,57 +1189,33 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
 		return -ENXIO;
 	}
 
-	dom_smmu = ACCESS_ONCE(smmu_domain->smmu);
-
 	/*
 	 * Sanity check the domain. We don't support domains across
 	 * different SMMUs.
 	 */
+	dom_smmu = ACCESS_ONCE(smmu_domain->smmu);
 	if (!dom_smmu) {
-		spin_lock_irqsave(&smmu_domain->lock, flags);
-		/*
-		 * make sure we're not racing with someone who might
-		 * have just attached and init'd the domain context
-		 */
-		dom_smmu = smmu_domain->smmu;
-		if (dom_smmu) {
-			spin_unlock_irqrestore(&smmu_domain->lock, flags);
-			goto have_dom_smmu;
-		}
 		/* Now that we have a master, we can finalise the domain */
 		ret = arm_smmu_init_domain_context(domain, smmu);
-		spin_unlock_irqrestore(&smmu_domain->lock, flags);
 		if (IS_ERR_VALUE(ret))
 			return ret;
-		dom_smmu = smmu_domain->smmu;
 
-		irq = smmu->irqs[smmu->num_global_irqs + cfg->irptndx];
-		ret = request_irq(irq, arm_smmu_context_fault, IRQF_SHARED,
-				"arm-smmu-context-fault", domain);
-		if (IS_ERR_VALUE(ret)) {
-			dev_err(smmu->dev, "failed to request context IRQ %d (%u)\n",
-				cfg->irptndx, irq);
-			cfg->irptndx = INVALID_IRPTNDX;
-			return ret;
-		}
+		dom_smmu = smmu_domain->smmu;
 	}
 
-have_dom_smmu:
-
 	if (dom_smmu != smmu) {
 		dev_err(dev,
 			"cannot attach to SMMU %s whilst already attached to domain on SMMU %s\n",
-			dev_name(smmu_domain->smmu->dev),
-			dev_name(smmu->dev));
+			dev_name(smmu_domain->smmu->dev), dev_name(smmu->dev));
 		return -EINVAL;
 	}
 
 	/* Looks ok, so add the device to the domain */
-	master_cfg = find_smmu_master_cfg(smmu_domain->smmu, dev);
-	if (!master_cfg)
+	cfg = find_smmu_master_cfg(smmu_domain->smmu, dev);
+	if (!cfg)
 		return -ENODEV;
 
-	return arm_smmu_domain_add_master(smmu_domain, master_cfg);
+	return arm_smmu_domain_add_master(smmu_domain, cfg);
 }
 
 static void arm_smmu_detach_dev(struct iommu_domain *domain, struct device *dev)

[PATCH v3] iommu/arm-smmu: avoid calling request_irq in atomic context

[Mitchel Humpherys]

On Wed, Jul 30 2014 at 08:31:14 AM, Will Deacon <will.deacon@arm.com> wrote:
> Hey Mitch,
>
> On Tue, Jul 29, 2014 at 07:11:15PM +0100, Mitchel Humpherys wrote:
>> request_irq shouldn't be called from atomic context since it might
>> sleep, but we're calling it with a spinlock held, resulting in:
>> 
>>     [    9.172202] BUG: sleeping function called from invalid context at kernel/mm/slub.c:926
>>     [    9.182989] in_atomic(): 1, irqs_disabled(): 128, pid: 1, name: swapper/0
>>     [    9.189762] CPU: 1 PID: 1 Comm: swapper/0 Tainted: G        W    3.10.40-gbc1b510b-38437-g55831d3bd9-dirty #97
>>     [    9.199757] [<c020c448>] (unwind_backtrace+0x0/0x11c) from [<c02097d0>] (show_stack+0x10/0x14)
>>     [    9.208346] [<c02097d0>] (show_stack+0x10/0x14) from [<c0301d74>] (kmem_cache_alloc_trace+0x3c/0x210)
>>     [    9.217543] [<c0301d74>] (kmem_cache_alloc_trace+0x3c/0x210) from [<c0276a48>] (request_threaded_irq+0x88/0x11c)
>>     [    9.227702] [<c0276a48>] (request_threaded_irq+0x88/0x11c) from [<c0931ca4>] (arm_smmu_attach_dev+0x188/0x858)
>>     [    9.237686] [<c0931ca4>] (arm_smmu_attach_dev+0x188/0x858) from [<c0212cd8>] (arm_iommu_attach_device+0x18/0xd0)
>>     [    9.247837] [<c0212cd8>] (arm_iommu_attach_device+0x18/0xd0) from [<c093314c>] (arm_smmu_test_probe+0x68/0xd4)
>>     [    9.257823] [<c093314c>] (arm_smmu_test_probe+0x68/0xd4) from [<c05aadd0>] (driver_probe_device+0x12c/0x330)
>>     [    9.267629] [<c05aadd0>] (driver_probe_device+0x12c/0x330) from [<c05ab080>] (__driver_attach+0x68/0x8c)
>>     [    9.277090] [<c05ab080>] (__driver_attach+0x68/0x8c) from [<c05a92d4>] (bus_for_each_dev+0x70/0x84)
>>     [    9.286118] [<c05a92d4>] (bus_for_each_dev+0x70/0x84) from [<c05aa3b0>] (bus_add_driver+0x100/0x244)
>>     [    9.295233] [<c05aa3b0>] (bus_add_driver+0x100/0x244) from [<c05ab5d0>] (driver_register+0x9c/0x124)
>>     [    9.304347] [<c05ab5d0>] (driver_register+0x9c/0x124) from [<c0933088>] (arm_smmu_test_init+0x14/0x38)
>>     [    9.313635] [<c0933088>] (arm_smmu_test_init+0x14/0x38) from [<c0200618>] (do_one_initcall+0xb8/0x160)
>>     [    9.322926] [<c0200618>] (do_one_initcall+0xb8/0x160) from [<c1200b7c>] (kernel_init_freeable+0x108/0x1cc)
>>     [    9.332564] [<c1200b7c>] (kernel_init_freeable+0x108/0x1cc) from [<c0b924b0>] (kernel_init+0xc/0xe4)
>>     [    9.341675] [<c0b924b0>] (kernel_init+0xc/0xe4) from [<c0205e38>] (ret_from_fork+0x14/0x3c)
>> 
>> Fix this by moving the request_irq out of the critical section. This
>> should be okay since smmu_domain->smmu is still being protected by the
>> critical section. Also, we still don't program the Stream Match Register
>> until after registering our interrupt handler so we shouldn't be missing
>> any interrupts.
>> 
>> Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>
>> ---
>> Changelog:
>> 
>>   - v3: rework irq request code to avoid requesting the irq every
>>         time a master is added to the domain
>>   - v2: return error code from request_irq on failure
>> ---
>>  drivers/iommu/arm-smmu.c | 73 +++++++++++++++++++++++++++---------------------
>>  1 file changed, 41 insertions(+), 32 deletions(-)
>
> I think this is correct, but we can do some cleanup now that you've moved
> all the locking into the conditional. Messy diff below, which would be much
> nicer sqaushed into your patch.
>
> What do you reckon?

Much cleaner, thanks. Just one question below.

>
> Will
>
> --->8
>
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index 572f5579d38b..e33df1a676ec 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -868,10 +868,15 @@ static void arm_smmu_init_context_bank(struct arm_smmu_domain *smmu_domain)
>  static int arm_smmu_init_domain_context(struct iommu_domain *domain,
>  					struct arm_smmu_device *smmu)
>  {
> -	int ret, start;
> +	int irq, start, ret = 0;
> +	unsigned long flags;
>  	struct arm_smmu_domain *smmu_domain = domain->priv;
>  	struct arm_smmu_cfg *cfg = &smmu_domain->cfg;
>  
> +	spin_lock_irqsave(&smmu_domain->lock, flags);
> +	if (smmu_domain->smmu)
> +		goto out_unlock;
> +
>  	if (smmu->features & ARM_SMMU_FEAT_TRANS_NESTED) {
>  		/*
>  		 * We will likely want to change this if/when KVM gets
> @@ -890,7 +895,7 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
>  	ret = __arm_smmu_alloc_bitmap(smmu->context_map, start,
>  				      smmu->num_context_banks);
>  	if (IS_ERR_VALUE(ret))
> -		return ret;
> +		goto out_unlock;
>  
>  	cfg->cbndx = ret;
>  	if (smmu->version == 1) {
> @@ -902,7 +907,22 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
>  
>  	ACCESS_ONCE(smmu_domain->smmu) = smmu;
>  	arm_smmu_init_context_bank(smmu_domain);
> +	spin_unlock_irqrestore(&smmu_domain->lock, flags);
> +
> +	irq = smmu->irqs[smmu->num_global_irqs + cfg->irptndx];
> +	ret = request_irq(irq, arm_smmu_context_fault, IRQF_SHARED,
> +			  "arm-smmu-context-fault", smmu_domain);
> +	if (IS_ERR_VALUE(ret)) {
> +		dev_err(smmu->dev, "failed to request context IRQ %d (%u)\n",
> +			cfg->irptndx, irq);
> +		cfg->irptndx = INVALID_IRPTNDX;

We want to return ret here due to the request_irq failure, right?

> +	}
> +
>  	return 0;
> +
> +out_unlock:
> +	spin_unlock_irqrestore(&smmu_domain->lock, flags);
> +	return ret;
>  }



-Mitch

-- 
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[PATCH v3] iommu/arm-smmu: avoid calling request_irq in atomic context

[Will Deacon]

On Wed, Jul 30, 2014 at 05:51:48PM +0100, Mitchel Humpherys wrote:
> On Wed, Jul 30 2014 at 08:31:14 AM, Will Deacon <will.deacon@arm.com> wrote:
> > On Tue, Jul 29, 2014 at 07:11:15PM +0100, Mitchel Humpherys wrote:
> >> Changelog:
> >> 
> >>   - v3: rework irq request code to avoid requesting the irq every
> >>         time a master is added to the domain
> >>   - v2: return error code from request_irq on failure
> >> ---
> >>  drivers/iommu/arm-smmu.c | 73 +++++++++++++++++++++++++++---------------------
> >>  1 file changed, 41 insertions(+), 32 deletions(-)
> >
> > I think this is correct, but we can do some cleanup now that you've moved
> > all the locking into the conditional. Messy diff below, which would be much
> > nicer sqaushed into your patch.
> >
> > What do you reckon?
> 
> Much cleaner, thanks. Just one question below.

[...]

> > @@ -902,7 +907,22 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
> >  
> >  	ACCESS_ONCE(smmu_domain->smmu) = smmu;
> >  	arm_smmu_init_context_bank(smmu_domain);
> > +	spin_unlock_irqrestore(&smmu_domain->lock, flags);
> > +
> > +	irq = smmu->irqs[smmu->num_global_irqs + cfg->irptndx];
> > +	ret = request_irq(irq, arm_smmu_context_fault, IRQF_SHARED,
> > +			  "arm-smmu-context-fault", smmu_domain);
> > +	if (IS_ERR_VALUE(ret)) {
> > +		dev_err(smmu->dev, "failed to request context IRQ %d (%u)\n",
> > +			cfg->irptndx, irq);
> > +		cfg->irptndx = INVALID_IRPTNDX;
> 
> We want to return ret here due to the request_irq failure, right?

Actually, no, and it's a subtle change introduced by this fix. Before, we
would partially tear-down the domain here by freeing the cbndx but actually,
that's racy as hell. The moment we drop the lock another device can attach
successfully to the domain we've set, so we can't safely tear things down at
that point. The best bet is to continue with the warning -- you end up with
a domain without a context interrupt, but that's not fatal to the driver.

If we returned an error, I can't think of a safe way to reset the domain.

Will