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Subject[PATCH] iommu/amd: Fix schedule-while-atomic BUG in initialization code
Hi Artem, Thomas,

On Wed, Jul 26, 2017 at 12:42:49PM +0200, Thomas Gleixner wrote:
> On Tue, 25 Jul 2017, Artem Savkov wrote:
>
> > Hi,
> >
> > Commit 1c3c5ea "sched/core: Enable might_sleep() and smp_processor_id()
> > checks early" seem to have uncovered an issue with amd-iommu/x2apic.
> >
> > Starting with that commit the following warning started to show up on AMD
> > systems during boot:
>
> > [ 0.160000] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:747
>
> > [ 0.160000] mutex_lock_nested+0x1b/0x20
> > [ 0.160000] register_syscore_ops+0x1d/0x70
> > [ 0.160000] state_next+0x119/0x910
> > [ 0.160000] iommu_go_to_state+0x29/0x30
> > [ 0.160000] amd_iommu_enable+0x13/0x23
> > [ 0.160000] irq_remapping_enable+0x1b/0x39
> > [ 0.160000] enable_IR_x2apic+0x91/0x196
> > [ 0.160000] default_setup_apic_routing+0x16/0x6e
> > [ 0.160000] native_smp_prepare_cpus+0x257/0x2d5

Thanks for the report!

> --- a/drivers/iommu/amd_iommu_init.c
> +++ b/drivers/iommu/amd_iommu_init.c
> @@ -2440,7 +2440,6 @@ static int __init state_next(void)
> break;
> case IOMMU_ACPI_FINISHED:
> early_enable_iommus();
> - register_syscore_ops(&amd_iommu_syscore_ops);
> x86_platform.iommu_shutdown = disable_iommus;
> init_state = IOMMU_ENABLED;
> break;
> @@ -2559,6 +2558,8 @@ static int __init amd_iommu_init(void)
> for_each_iommu(iommu)
> iommu_flush_all_caches(iommu);
> }
> + } else {
> + register_syscore_ops(&amd_iommu_syscore_ops);
> }
>
> return ret;

Yes, that should fix it, but I think its better to just move the
register_syscore_ops() call to a later initialization step, like in the
patch below. I tested it an will queue it to my iommu/fixes branch.

From 461242d7211c7777901b6ccdf349cc89235bd5da Mon Sep 17 00:00:00 2001
From: Joerg Roedel <jroedel@suse.de>
Date: Wed, 26 Jul 2017 14:17:55 +0200
Subject: [PATCH] iommu/amd: Fix schedule-while-atomic BUG in initialization
code

The register_syscore_ops() function takes a mutex and might
sleep. In the IOMMU initialization code it is invoked during
irq-remapping setup already, where irqs are disabled.

This causes a schedule-while-atomic bug:

BUG: sleeping function called from invalid context at kernel/locking/mutex.c:747
in_atomic(): 0, irqs_disabled(): 1, pid: 1, name: swapper/0
no locks held by swapper/0/1.
irq event stamp: 304
hardirqs last enabled at (303): [<ffffffff818a87b6>] _raw_spin_unlock_irqrestore+0x36/0x60
hardirqs last disabled at (304): [<ffffffff8235d440>] enable_IR_x2apic+0x79/0x196
softirqs last enabled at (36): [<ffffffff818ae75f>] __do_softirq+0x35f/0x4ec
softirqs last disabled at (31): [<ffffffff810c1955>] irq_exit+0x105/0x120
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.13.0-rc2.1.el7a.test.x86_64.debug #1
Hardware name: PowerEdge C6145 /040N24, BIOS 3.5.0 10/28/2014
Call Trace:
dump_stack+0x85/0xca
___might_sleep+0x22a/0x260
__might_sleep+0x4a/0x80
__mutex_lock+0x58/0x960
? iommu_completion_wait.part.17+0xb5/0x160
? register_syscore_ops+0x1d/0x70
? iommu_flush_all_caches+0x120/0x150
mutex_lock_nested+0x1b/0x20
register_syscore_ops+0x1d/0x70
state_next+0x119/0x910
iommu_go_to_state+0x29/0x30
amd_iommu_enable+0x13/0x23

Fix it by moving the register_syscore_ops() call to the next
initialization step, which runs with irqs enabled.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
drivers/iommu/amd_iommu_init.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
index 5cc597b383c7..372303700566 100644
--- a/drivers/iommu/amd_iommu_init.c
+++ b/drivers/iommu/amd_iommu_init.c
@@ -2440,11 +2440,11 @@ static int __init state_next(void)
break;
case IOMMU_ACPI_FINISHED:
early_enable_iommus();
- register_syscore_ops(&amd_iommu_syscore_ops);
x86_platform.iommu_shutdown = disable_iommus;
init_state = IOMMU_ENABLED;
break;
case IOMMU_ENABLED:
+ register_syscore_ops(&amd_iommu_syscore_ops);
ret = amd_iommu_init_pci();
init_state = ret ? IOMMU_INIT_ERROR : IOMMU_PCI_INIT;
enable_iommus_v2();
--
2.13.1
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