Re: [PULL 02/10] util/interval-tree: Use qatomic_set_mb in rb_link_node

[Richard Henderson <richard.henderson@linaro.org>]

On 8/4/23 02:02, Michael Tokarev wrote:
> 01.08.2023 00:02, Richard Henderson wrote:
>> Ensure that the stores to rb_left and rb_right are complete before
>> inserting the new node into the tree.  Otherwise a concurrent reader
>> could see garbage in the new leaf.
>>
>> Cc: qemu-stable@nongnu.org
>> Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>> ---
>>   util/interval-tree.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/util/interval-tree.c b/util/interval-tree.c
>> index 5a0ad21b2d..759562db7d 100644
>> --- a/util/interval-tree.c
>> +++ b/util/interval-tree.c
>> @@ -128,7 +128,11 @@ static inline void rb_link_node(RBNode *node, RBNode *parent, 
>> RBNode **rb_link)
>>       node->rb_parent_color = (uintptr_t)parent;
>>       node->rb_left = node->rb_right = NULL;
>> -    qatomic_set(rb_link, node);
>> +    /*
>> +     * Ensure that node is initialized before insertion,
>> +     * as viewed by a concurrent search.
>> +     */
>> +    qatomic_set_mb(rb_link, node);
> 
> FWIW, there's no qatomic_set_mb() in 8.0 and before, so this can not be
> directly applied to stable-8.0.  This commit is missing in 8.0 before
> qatomic_set_mb() can be used:
> 
> commit 06831001ac8949b0801e0d20c347d97339769a20
> Author: Paolo Bonzini <pbonzini@redhat.com>
> Date:   Fri Mar 3 14:37:51 2023 +0100
> 
>      atomics: eliminate mb_read/mb_set
> 
> I don't think it's a good idea to back-port this commit to stable-8.0.
> 
> How do you think we can solve this for 8.0?

The function is called qatomic_mb_set instead of qatomic_set_mb in stable-8.0.


r~