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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Fri, 26 Jun 2015 18:20:04 +0200
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Subject: Re: [Qemu-devel] [RFC PATCH V6 05/18] protect TBContext with
	tb_lock.
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To: fred.konrad@greensocs.com, qemu-devel@nongnu.org, mttcg@listserver.greensocs.com
Cc: peter.maydell@linaro.org, a.spyridakis@virtualopensystems.com, mark.burton@greensocs.com, agraf@suse.de, alistair.francis@xilinx.com, guillaume.delbergue@greensocs.com, alex.bennee@linaro.org



On 26/06/2015 16:47, fred.konrad@greensocs.com wrote:
> @@ -273,8 +274,9 @@ static TranslationBlock *tb_find_slow(CPUArchState *env,
>      ptb1 = &tcg_ctx.tb_ctx.tb_phys_hash[h];
>      for(;;) {
>          tb = *ptb1;
> -        if (!tb)
> -            goto not_found;
> +        if (!tb) {
> +            return tb;
> +        }

You are dereferencing tb outside the lock. You need a
smp_read_barrier_depends() here, and a smp_wmb() at the beginning of
tb_link_page.

Paolo

>          if (tb->pc == pc &&