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Cc:     baolu.lu@linux.intel.com, iommu@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] iommu/vt-d: silence a RCU-list debugging warning
To:     Qian Cai <cai@lca.pw>, jroedel@suse.de
References: <20200317150326.1659-1-cai@lca.pw>
From:   Lu Baolu <baolu.lu@linux.intel.com>
Message-ID: <36b9e69b-ee3f-c17d-1788-64448ce8bc14@linux.intel.com>
Date:   Wed, 18 Mar 2020 13:27:53 +0800
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On 2020/3/17 23:03, Qian Cai wrote:
> dmar_find_atsr() calls list_for_each_entry_rcu() outside of an RCU read
> side critical section but with dmar_global_lock held. Silence this
> false positive.
> 
>   drivers/iommu/intel-iommu.c:4504 RCU-list traversed in non-reader section!!
>   1 lock held by swapper/0/1:
>   #0: ffffffff9755bee8 (dmar_global_lock){+.+.}, at: intel_iommu_init+0x1a6/0xe19
> 
>   Call Trace:
>    dump_stack+0xa4/0xfe
>    lockdep_rcu_suspicious+0xeb/0xf5
>    dmar_find_atsr+0x1ab/0x1c0
>    dmar_parse_one_atsr+0x64/0x220
>    dmar_walk_remapping_entries+0x130/0x380
>    dmar_table_init+0x166/0x243
>    intel_iommu_init+0x1ab/0xe19
>    pci_iommu_init+0x1a/0x44
>    do_one_initcall+0xae/0x4d0
>    kernel_init_freeable+0x412/0x4c5
>    kernel_init+0x19/0x193
> 
> Signed-off-by: Qian Cai <cai@lca.pw>

How about changing the commit subject to
"iommu/vt-d: Silence RCU-list debugging warning in dmar_find_atsr()"?

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

Best regards,
baolu

> ---
>   drivers/iommu/intel-iommu.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 4be549478691..ef0a5246700e 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -4501,7 +4501,8 @@ static struct dmar_atsr_unit *dmar_find_atsr(struct acpi_dmar_atsr *atsr)
>   	struct dmar_atsr_unit *atsru;
>   	struct acpi_dmar_atsr *tmp;
>   
> -	list_for_each_entry_rcu(atsru, &dmar_atsr_units, list) {
> +	list_for_each_entry_rcu(atsru, &dmar_atsr_units, list,
> +				dmar_rcu_check()) {
>   		tmp = (struct acpi_dmar_atsr *)atsru->hdr;
>   		if (atsr->segment != tmp->segment)
>   			continue;
>