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From:   Qian Cai <cai@lca.pw>
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Subject: Re: [PATCH v16 13/25] mm: pagewalk: Don't lock PTEs for walk_page_range_novma()
Date:   Wed, 11 Dec 2019 12:19:35 -0500
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References: <e0fd5594-fb4e-9ead-e582-544f47cb1f8b@arm.com>
Cc:     kbuild test robot <lkp@intel.com>,
        Mark Rutland <Mark.Rutland@arm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Dave Hansen <dave.hansen@linux.intel.com>, linux-mm@kvack.org,
        "H. Peter Anvin" <hpa@zytor.com>, Will Deacon <will@kernel.org>,
        "Liang, Kan" <kan.liang@linux.intel.com>, x86@kernel.org,
        Ingo Molnar <mingo@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
        =?utf-8?Q?J=C3=A9r=C3=B4me_Glisse?= <jglisse@redhat.com>,
        Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-arm-kernel@lists.infradead.org, kbuild-all@lists.01.org,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        linux-kernel@vger.kernel.org, James Morse <James.Morse@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>
In-Reply-To: <e0fd5594-fb4e-9ead-e582-544f47cb1f8b@arm.com>
To:     Steven Price <Steven.Price@arm.com>
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> On Dec 11, 2019, at 10:54 AM, Steven Price <Steven.Price@arm.com> wrote:
>=20
> I believe this is a false positive (although the trace here is useless).
> This patch adds a conditional lock/unlock:
>=20
> pte =3D walk->no_vma ? pte_offset_map(pmd, addr) :
>             pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
> ...
> if (!walk->no_vma)
>    spin_unlock(ptl);
> pte_unmap(pte);
>=20
> I'm not sure how to match sparse happy about that. Is the only option to
> have two versions of the walk_pte_range() function? One which takes the
> lock and one which doesn't.

Or just ignore the sparse false positive without complicating the code furth=
er.=