On 18.01.2018 18:07, Andrey Ryabinin wrote:
> We ->put_page() into tcache twice w/o ->get_page() in between, resulting in:
>
> WARNING: CPU: 1 PID: 1936 at mm/tcache.c:752 tcache_attach_page+0x218/0x240
>
> Call Trace:
> dump_stack+0x19/0x1b
> add_taint+0x32/0x70
> __warn+0xaa/0x100
> warn_slowpath_null+0x1d/0x20
> tcache_attach_page+0x218/0x240
> tcache_cleancache_put_page+0xdc/0x150
> __cleancache_put_page+0xa2/0xf0
> __delete_from_page_cache+0x309/0x370
> __remove_mapping+0x91/0x180
> shrink_page_list+0x5a8/0xa80
> shrink_inactive_list+0x1da/0x710
> shrink_lruvec+0x3a1/0x760
> shrink_zone+0x15b/0x310
> do_try_to_free_pages+0x1a0/0x610
> try_to_free_mem_cgroup_pages+0xeb/0x190
> mem_cgroup_reclaim+0x63/0x140
> try_charge+0x287/0x560
> mem_cgroup_try_charge+0x7a/0x130
> __add_to_page_cache_locked+0x97/0x2f0
> add_to_page_cache_lru+0x37/0xb0
> mpage_readpages+0xb5/0x150
> ext4_readpages+0x3c/0x40 [ext4]
> __do_page_cache_readahead+0x1cd/0x250
> ondemand_readahead+0x116/0x230
> page_cache_async_readahead+0xa8/0xc0
>
> It's because we put all clean pages into cleancache, but in some cases
> we may never read those pages from cleancache. E.g. see do_mpage_readpage(),
> there are many case when cleancache_get_page() is not called.
>
> Fix this by invalidating such existing page during ->put_page().
>
> https://jira.sw.ru/browse/PSBM-80712
> Signed-off-by: Andrey Ryabinin <aryabi...@virtuozzo.com>
Reviewed-by: Kirill Tkhai <ktk...@virtuozzo.com>
> ---
>
> Changes since v1:
> - add "ret = 0", as se must return number of put pages from
> tcache_cleancache_put_page()
> mm/tcache.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/mm/tcache.c b/mm/tcache.c
> index a45af63fbd1b..9710531731ab 100644
> --- a/mm/tcache.c
> +++ b/mm/tcache.c
> @@ -749,7 +749,6 @@ static int tcache_page_tree_insert(struct tcache_node
> *node, pgoff_t index,
> }
>
> err = radix_tree_insert(&node->page_tree, index, page);
> - WARN_ON(err == -EEXIST);
> if (!err) {
> if (!node->nr_pages++)
> tcache_hold_node(node);
> @@ -1256,9 +1255,18 @@ static int tcache_cleancache_put_page(int pool_id,
> cache_page = tcache_alloc_page(node->pool);
> if (cache_page) {
> copy_highpage(cache_page, page);
> - if (tcache_attach_page(node, index, cache_page)) {
> + ret = tcache_attach_page(node, index, cache_page);
> + if (ret) {
> + if (ret == -EEXIST) {
> + struct page *page;
> +
> + page = tcache_detach_page(node, index,
> false);
> + if (page)
> + tcache_put_page(page);
> + }
> if (put_page_testzero(cache_page))
> tcache_put_page(cache_page);
> + ret = 0;
> } else
> ret = 1;
> }
>
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