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

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Date:   Fri, 21 Oct 2022 15:22:48 +0200
From:   Andrea Parri <parri.andrea@...il.com>
To:     Tong Tiangen <tongtiangen@...wei.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

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