Re: [BUG REPORT] ZSWAP: theoretical race condition issues

From: Bob Liu
Date: Wed Sep 25 2013 - 04:31:16 EST

On Wed, Sep 25, 2013 at 4:09 PM, Weijie Yang <> wrote:
> I think I find a new issue, for integrity of this mail thread, I reply
> to this mail.
> It is a concurrence issue either, when duplicate store and reclaim
> concurrentlly.
> zswap entry x with offset A is already stored in zswap backend.
> Consider the following scenario:
> thread 0: reclaim entry x (get refcount, but not call zswap_get_swap_cache_page)
> thread 1: store new page with the same offset A, alloc a new zswap entry y.
> store finished. shrink_page_list() call __remove_mapping(), and now
> it is not in swap_cache

But I don't think swap layer will call zswap with the same offset A.

> thread 0: zswap_get_swap_cache_page called. old page data is added to swap_cache
> Now, swap cache has old data rather than new data for offset A.
> error will happen If do_swap_page() get page from swap_cache.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at