linux-kernel - Re: linux-next: manual merge of the akpm-current tree with the tip tree

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Message-ID: <20170814083839.GD26913@bbox>
Date:   Mon, 14 Aug 2017 17:38:39 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Nadav Amit <namit@...are.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linus <torvalds@...ux-foundation.org>
Subject: Re: linux-next: manual merge of the akpm-current tree with the tip
 tree

Hi Nadav,

On Mon, Aug 14, 2017 at 05:07:19AM +0000, Nadav Amit wrote:
< snip >

> For some reason (I would assume intentional), all the examples here first
> “do not modify” the PTE, and then modify it - which is not an “interesting”
> case. However, based on what I understand on the memory barriers, I think
> there is indeed a missing barrier before reading it in
> mm_tlb_flush_nested(). IIUC using smp_mb__after_unlock_lock() in this case,

memory-barrier.txt always scares me. I have read it for a while
and IIUC, it seems semantic of spin_unlock(&same_pte) would be
enough without some memory-barrier inside mm_tlb_flush_nested.

I would be missing something totally.

Could you explain what kinds of sequence you have in mind to
have such problem?

Thanks.