From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f178.google.com (mail-wi0-f178.google.com [209.85.212.178]) by kanga.kvack.org (Postfix) with ESMTP id 4719E28029D for ; Sun, 5 Jul 2015 20:17:35 -0400 (EDT) Received: by wiwl6 with SMTP id l6so270030988wiw.0 for ; Sun, 05 Jul 2015 17:17:34 -0700 (PDT) Received: from mail-wi0-x232.google.com (mail-wi0-x232.google.com. [2a00:1450:400c:c05::232]) by mx.google.com with ESMTPS id tm3si27313325wjc.126.2015.07.05.17.17.33 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 05 Jul 2015 17:17:33 -0700 (PDT) Received: by wiclp1 with SMTP id lp1so6643167wic.0 for ; Sun, 05 Jul 2015 17:17:33 -0700 (PDT) From: Nicolai Stange Subject: [PATCH] mm/page_alloc: deferred meminit: replace rwsem with completion Date: Mon, 06 Jul 2015 02:17:30 +0200 Message-ID: <87k2uecf6t.fsf@gmail.com> MIME-Version: 1.0 Content-Type: text/plain Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Mel Gorman , Vlastimil Babka , Johannes Weiner , Michal Hocko , Joonsoo Kim , David Rientjes , Alexander Duyck , Sasha Levin , linux-mm@kvack.org, linux-kernel@vger.kernel.org Commit 0e1cc95b4cc7 ("mm: meminit: finish initialisation of struct pages before basic setup") introduced a rwsem to signal completion of the initialization workers. Lockdep complains about possible recursive locking: ============================================= [ INFO: possible recursive locking detected ] 4.1.0-12802-g1dc51b8 #3 Not tainted --------------------------------------------- swapper/0/1 is trying to acquire lock: (pgdat_init_rwsem){++++.+}, at: [] page_alloc_init_late+0xc7/0xe6 but task is already holding lock: (pgdat_init_rwsem){++++.+}, at: [] page_alloc_init_late+0x3e/0xe6 Replace the rwsem by a completion together with an atomic "outstanding work counter". Signed-off-by: Nicolai Stange --- mm/page_alloc.c | 34 +++++++++++++++++++++++++++------- 1 file changed, 27 insertions(+), 7 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 506eac8..3886e66 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -18,7 +18,9 @@ #include #include #include -#include +#include +#include +#include #include #include #include @@ -1062,7 +1064,20 @@ static void __init deferred_free_range(struct page *page, __free_pages_boot_core(page, pfn, 0); } -static __initdata DECLARE_RWSEM(pgdat_init_rwsem); +/* counter and completion tracking outstanding deferred_init_memmap() + threads */ +static atomic_t pgdat_init_n_undone __initdata; +static __initdata DECLARE_COMPLETION(pgdat_init_all_done_comp); + +static inline void __init pgdat_init_report_one_done(void) +{ + /* Write barrier is paired with read barrier in + page_alloc_init_late(). It makes all writes visible to + readers seeing our decrement on pgdat_init_n_undone. */ + smp_wmb(); + if (atomic_dec_and_test(&pgdat_init_n_undone)) + complete(&pgdat_init_all_done_comp); +} /* Initialise remaining memory on a node */ static int __init deferred_init_memmap(void *data) @@ -1079,7 +1094,7 @@ static int __init deferred_init_memmap(void *data) const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id); if (first_init_pfn == ULONG_MAX) { - up_read(&pgdat_init_rwsem); + pgdat_init_report_one_done(); return 0; } @@ -1179,7 +1194,8 @@ free_range: pr_info("node %d initialised, %lu pages in %ums\n", nid, nr_pages, jiffies_to_msecs(jiffies - start)); - up_read(&pgdat_init_rwsem); + + pgdat_init_report_one_done(); return 0; } @@ -1187,14 +1203,18 @@ void __init page_alloc_init_late(void) { int nid; + /* There will be num_node_state(N_MEMORY) threads */ + atomic_set(&pgdat_init_n_undone, num_node_state(N_MEMORY)); for_each_node_state(nid, N_MEMORY) { - down_read(&pgdat_init_rwsem); kthread_run(deferred_init_memmap, NODE_DATA(nid), "pgdatinit%d", nid); } /* Block until all are initialised */ - down_write(&pgdat_init_rwsem); - up_write(&pgdat_init_rwsem); + wait_for_completion(&pgdat_init_all_done_comp); + + /* Paired with write barrier in deferred_init_memmap(), + ensures a consistent view of all its writes. */ + smp_rmb(); } #endif /* CONFIG_DEFERRED_STRUCT_PAGE_INIT */ -- 2.4.5 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org