linux-kernel - Re: [PATCH 2/2] arm64: tlb: skip tlbi broadcast for single threaded TLB flushes

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Date:   Wed, 12 Feb 2020 07:57:57 -0500
From:   Andrea Arcangeli <aarcange@...hat.com>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Will Deacon <will@...nel.org>, Jon Masters <jcm@...masters.org>,
        Rafael Aquini <aquini@...hat.com>,
        Mark Salter <msalter@...hat.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/2] arm64: tlb: skip tlbi broadcast for single threaded
 TLB flushes

Hello,

On Tue, Feb 11, 2020 at 02:00:25PM +0000, Catalin Marinas wrote:
> I think there is another race here. IIUC, the assumption you make is
> that when mm_users <= 1 && mm_count == 1, the only active user of this
> pgd/ASID is on the CPU doing the TLBI. This is not the case for
> try_to_unmap() where the above condition may be true but the active
> thread on a different CPU won't notice the local TLBI.

The "current->mm == mm" check is what shall prevent the above.

Thanks,
Andrea