* [Qemu-devel] [PATCH] exec.c: Use atomic_rcu_read() to access dispatch in memory_region_section_get_iotlb()
@ 2015-07-20 11:27 Peter Maydell
2015-07-21 8:50 ` Paolo Bonzini
0 siblings, 1 reply; 2+ messages in thread
From: Peter Maydell @ 2015-07-20 11:27 UTC (permalink / raw)
To: qemu-devel; +Cc: Paolo Bonzini, patches
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 <peter.maydell@linaro.org>
---
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;
}
--
1.9.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [Qemu-devel] [PATCH] exec.c: Use atomic_rcu_read() to access dispatch in memory_region_section_get_iotlb()
2015-07-20 11:27 [Qemu-devel] [PATCH] exec.c: Use atomic_rcu_read() to access dispatch in memory_region_section_get_iotlb() Peter Maydell
@ 2015-07-21 8:50 ` Paolo Bonzini
0 siblings, 0 replies; 2+ messages in thread
From: Paolo Bonzini @ 2015-07-21 8:50 UTC (permalink / raw)
To: Peter Maydell, qemu-devel; +Cc: patches
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 <peter.maydell@linaro.org>
> ---
> 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
^ permalink raw reply [flat|nested] 2+ messages in thread
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2015-07-20 11:27 [Qemu-devel] [PATCH] exec.c: Use atomic_rcu_read() to access dispatch in memory_region_section_get_iotlb() Peter Maydell
2015-07-21 8:50 ` Paolo Bonzini
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