linux-kernel - Re: [PATCH 2/4] mm/tlb: Remove tlb_remove

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Message-ID: <20180823134041.GB1496@brain-police>
Date:   Thu, 23 Aug 2018 14:40:41 +0100
From:   Will Deacon <will.deacon@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     torvalds@...ux-foundation.org, luto@...nel.org, x86@...nel.org,
        bp@...en8.de, riel@...riel.com, jannh@...gle.com,
        ascannell@...gle.com, dave.hansen@...el.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Nicholas Piggin <npiggin@...il.com>,
        David Miller <davem@...emloft.net>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH 2/4] mm/tlb: Remove tlb_remove_table() non-concurrent
 condition

On Wed, Aug 22, 2018 at 05:30:14PM +0200, Peter Zijlstra wrote:
> Will noted that only checking mm_users is incorrect; we should also
> check mm_count in order to cover CPUs that have a lazy reference to
> this mm (and could do speculative TLB operations).
> 
> If removing this turns out to be a performance issue, we can
> re-instate a more complete check, but in tlb_table_flush() eliding the
> call_rcu_sched().
> 
> Cc: stable@...nel.org
> Cc: Nicholas Piggin <npiggin@...il.com>
> Cc: David Miller <davem@...emloft.net>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Fixes: 267239116987 ("mm, powerpc: move the RCU page-table freeing into generic code")
> Reported-by: Will Deacon <will.deacon@....com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  mm/memory.c |    9 ---------
>  1 file changed, 9 deletions(-)

Acked-by: Will Deacon <will.deacon@....com>

Cheers,

Will