linux-kernel - Re: [PATCH] iommu/vt-d: fix RCU-list bugs in intel_iommu

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Date:   Sat, 7 Mar 2020 19:52:27 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Qian Cai <cai@....pw>, jroedel@...e.de
Cc:     baolu.lu@...ux.intel.com, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/vt-d: fix RCU-list bugs in intel_iommu_init

Hi,

On 2020/3/6 4:00, Qian Cai wrote:
> There are several places traverse RCU-list without holding any lock in
> intel_iommu_init(). Fix them by acquiring dmar_global_lock.
> 
>   WARNING: suspicious RCU usage
>   -----------------------------
>   drivers/iommu/intel-iommu.c:5216 RCU-list traversed in non-reader section!!
> 
>   other info that might help us debug this:
> 
>   rcu_scheduler_active = 2, debug_locks = 1
>   no locks held by swapper/0/1.
> 
>   Call Trace:
>    dump_stack+0xa0/0xea
>    lockdep_rcu_suspicious+0x102/0x10b
>    intel_iommu_init+0x947/0xb13
>    pci_iommu_init+0x26/0x62
>    do_one_initcall+0xfe/0x500
>    kernel_init_freeable+0x45a/0x4f8
>    kernel_init+0x11/0x139
>    ret_from_fork+0x3a/0x50
>   DMAR: Intel(R) Virtualization Technology for Directed I/O
> 
> Fixes: d8190dc63886 ("iommu/vt-d: Enable DMA remapping after rmrr mapped")
> Signed-off-by: Qian Cai <cai@....pw>

Thanks for the fix.

Acked-by: Lu Baolu <baolu.lu@...ux.intel.com>

Best regards,
baolu

> ---
>   drivers/iommu/intel-iommu.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 6fa6de2b6ad5..bc138ceb07bc 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -5193,6 +5193,7 @@ int __init intel_iommu_init(void)
>   
>   	init_iommu_pm_ops();
>   
> +	down_read(&dmar_global_lock);
>   	for_each_active_iommu(iommu, drhd) {
>   		iommu_device_sysfs_add(&iommu->iommu, NULL,
>   				       intel_iommu_groups,
> @@ -5200,6 +5201,7 @@ int __init intel_iommu_init(void)
>   		iommu_device_set_ops(&iommu->iommu, &intel_iommu_ops);
>   		iommu_device_register(&iommu->iommu);
>   	}
> +	up_read(&dmar_global_lock);
>   
>   	bus_set_iommu(&pci_bus_type, &intel_iommu_ops);
>   	if (si_domain && !hw_pass_through)
> @@ -5210,7 +5212,6 @@ int __init intel_iommu_init(void)
>   	down_read(&dmar_global_lock);
>   	if (probe_acpi_namespace_devices())
>   		pr_warn("ACPI name space devices didn't probe correctly\n");
> -	up_read(&dmar_global_lock);
>   
>   	/* Finally, we enable the DMA remapping hardware. */
>   	for_each_iommu(iommu, drhd) {
> @@ -5219,6 +5220,8 @@ int __init intel_iommu_init(void)
>   
>   		iommu_disable_protect_mem_regions(iommu);
>   	}
> +	up_read(&dmar_global_lock);
> +
>   	pr_info("Intel(R) Virtualization Technology for Directed I/O\n");
>   
>   	intel_iommu_enabled = 1;
>