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Re: [Qemu-devel] [PATCH] exec.c: Use atomic_rcu_read() to access dispatc
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH] exec.c: Use atomic_rcu_read() to access dispatch in memory_region_section_get_iotlb() |
Date: |
Tue, 21 Jul 2015 10:50:00 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.0.1 |
On 20/07/2015 13:27, Peter Maydell wrote:
> When accessing the dispatch pointer in an AddressSpace within an RCU
> critical section we should always use atomic_rcu_read(). Fix an
> access within memory_region_section_get_iotlb() which was incorrectly
> doing a direct pointer access.
>
> Signed-off-by: Peter Maydell <address@hidden>
> ---
> I discussed this on IRC with Paolo a while back, and IIRC he said
> that although this is a bug it's not one that can currently have
> any ill effects, though I forget why (probably because this code
> path is TCG only and TCG is single-threaded right now).
>
> exec.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/exec.c b/exec.c
> index 7d60e15..0a4a0c5 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -954,7 +954,10 @@ hwaddr memory_region_section_get_iotlb(CPUState *cpu,
> iotlb |= PHYS_SECTION_ROM;
> }
> } else {
> - iotlb = section - section->address_space->dispatch->map.sections;
> + AddressSpaceDispatch *d;
> +
> + d = atomic_rcu_read(§ion->address_space->dispatch);
> + iotlb = section - d->map.sections;
> iotlb += xlat;
> }
>
Thanks, queued for next 2.4 pull request.
Paolo