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

From: [email-masked] (Will Deacon)
Date: Wed, 30 Jul 2014 16:31:14 +0100

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 <[email-masked]>
> ---
> 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)