linux-kernel - Re: [PATCH v16 13/25] mm: pagewalk: Don't lock PTEs for walk_page_range

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Date:   Wed, 11 Dec 2019 12:19:35 -0500
From:   Qian Cai <cai@....pw>
To:     Steven Price <Steven.Price@....com>
Cc:     kbuild test robot <lkp@...el.com>,
        Mark Rutland <Mark.Rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, linux-mm@...ck.org,
        "H. Peter Anvin" <hpa@...or.com>, Will Deacon <will@...nel.org>,
        "Liang, Kan" <kan.liang@...ux.intel.com>, x86@...nel.org,
        Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        Jérôme Glisse <jglisse@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org, kbuild-all@...ts.01.org,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-kernel@...r.kernel.org, James Morse <James.Morse@....com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v16 13/25] mm: pagewalk: Don't lock PTEs for walk_page_range_novma()



> On Dec 11, 2019, at 10:54 AM, Steven Price <Steven.Price@....com> wrote:
> 
> I believe this is a false positive (although the trace here is useless).
> This patch adds a conditional lock/unlock:
> 
> pte = 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);
> 
> 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 further.