linux-kernel - Re: [PATCH] riscv: fix race when vmap stack overflow

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Message-ID: <f1eb4756-e1e1-1f12-e767-a69a891786d6@huawei.com>
Date:   Fri, 21 Oct 2022 21:46:23 +0800
From:   Tong Tiangen <tongtiangen@...wei.com>
To:     Andrea Parri <parri.andrea@...il.com>
CC:     Guo Ren <guoren@...nel.org>, Jisheng Zhang <jszhang@...nel.org>,
        "Paul Walmsley" <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        <linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] riscv: fix race when vmap stack overflow



在 2022/10/21 21:22, Andrea Parri 写道:
> Hi Tong,
>   
>>>> I use atomic_set_release here, because I need earlier memory
>>>> operations finished to make sure the sp is ready then set the spin
>>>> flag.
> 
>> 	Consider this implementation:)
>>
>> 	smp_store_mb(&spin_shadow_stack, 0);
> 
> smp_store_mb() has "WRITE_ONCE(); smp_mb()" semantics; so it doesn't
> guarantee that the store to spin_shadow_stack is ordered after program
> -order earlier memory accesses.
> 
>    Andrea
> .

Hi Andrea:

IIUC, the earlier memory access amoswap.aqrl, here .aqrl guarantee it.
But anyway, consider we don't care about performance here, using 
smp_store_release()(add barrier()) surely right.

Thanks,
Tong.