[sheepdog] [PATCH] fix a race in get_obj_list()

[星刻]

On 05/25/2012 03:55 PM, levin li wrote:
> From: levin li <xingke.lwp at taobao.com>
>
> Reseting the object list buffer should not be locked by the
> reader lock, but should be locked by a writer lock, or else
> it's a race.
>
> Signed-off-by: levin li <xingke.lwp at taobao.com>
> ---
>  sheep/object_list_cache.c |   15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/sheep/object_list_cache.c b/sheep/object_list_cache.c
> index 0eb5223..110f810 100644
> --- a/sheep/object_list_cache.c
> +++ b/sheep/object_list_cache.c
> @@ -143,22 +143,27 @@ int get_obj_list(const struct sd_list_req *hdr, struct sd_list_rsp *rsp, void *d
>       struct objlist_cache_entry *entry;
>       struct rb_node *p;
>
> -     rsp->data_length = obj_list_cache.cache_size * sizeof(uint64_t);
> -
>       pthread_rwlock_rdlock(&obj_list_cache.lock);
> -     if (obj_list_cache.tree_version == obj_list_cache.buf_version)
> +     rsp->data_length = obj_list_cache.cache_size * sizeof(uint64_t);
> +     if (obj_list_cache.tree_version == obj_list_cache.buf_version) {
>               memcpy(list, obj_list_cache.buffer.buf, rsp->data_length);
> -     else {
> +             pthread_rwlock_unlock(&obj_list_cache.lock);
> +     } else {
>               for (p = rb_first(&obj_list_cache.root); p; p = rb_next(p)) {
>                       entry = rb_entry(p, struct objlist_cache_entry, node);
>                       list[nr++] = entry->oid;
>               }
> +             pthread_rwlock_unlock(&obj_list_cache.lock);
>
> +             pthread_rwlock_wrlock(&obj_list_cache.lock);
> +             if (obj_list_cache.tree_version == obj_list_cache.buf_version)
> +                     goto unlock;
>               strbuf_reset(&obj_list_cache.buffer);
>               strbuf_add(&obj_list_cache.buffer, list, nr * sizeof(uint64_t));
>               obj_list_cache.buf_version = obj_list_cache.tree_version;
> +unlock:
> +             pthread_rwlock_unlock(&obj_list_cache.lock);
>       }
> -     pthread_rwlock_unlock(&obj_list_cache.lock);
>
>       return SD_RES_SUCCESS;
>  }

Hi, Christoph

Whether this patch can fix the problem you mentioned here:
http://lists.wpkg.org/pipermail/sheepdog/2012-May/004040.html

thanks,

levin

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