linux-kernel - Re: [PATCH 5.10 074/243] iommu/arm-smmu: Fix arm_smmu_device refcount leak when arm_smmu_rpm

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Message-ID: <20210720220445.GA1557@amd>
Date:   Wed, 21 Jul 2021 00:04:46 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Xin Tan <tanxin.ctf@...il.com>, Will Deacon <will@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 5.10 074/243] iommu/arm-smmu: Fix arm_smmu_device
 refcount leak when arm_smmu_rpm_get fails

Hi!

> From: Xiyu Yang <xiyuyang19@...an.edu.cn>
> 
> [ Upstream commit 1adf30f198c26539a62d761e45af72cde570413d ]
> 
> arm_smmu_rpm_get() invokes pm_runtime_get_sync(), which increases the
> refcount of the "smmu" even though the return value is less than 0.

Yes.

> The reference counting issue happens in some error handling paths of
> arm_smmu_rpm_get() in its caller functions. When arm_smmu_rpm_get()
> fails, the caller functions forget to decrease the refcount of "smmu"
> increased by arm_smmu_rpm_get(), causing a refcount leak.

Yes, some error paths do that. But some callers (arm_smmu_map,
arm_smmu_unmap, arm_smmu_flush_iotlb_all, ...) ignore return value of
arm_smmu_rpm_get().

> Fix this issue by calling pm_runtime_resume_and_get() instead of
> pm_runtime_get_sync() in arm_smmu_rpm_get(), which can keep the refcount
> balanced in case of failure.

So no, this is not fixed; it is just unbalanced in the other (more
dangerous) direction now.

Best regards,
								Pavel
								
-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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