linux-kernel - Re: [mminit] [ INFO: possible recursive locking detected ]

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Date:	Mon, 20 Jul 2015 22:01:11 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, peterz@...radead.org,
	nicstange@...il.com,
	Linux Memory Management List <linux-mm@...ck.org>,
	linux-kernel@...r.kernel.org, LKP <lkp@...org>
Subject: Re: [mminit] [ INFO: possible recursive locking detected ]

Hi Mel,

On Tue, Jul 14, 2015 at 11:31:08AM +0100, Mel Gorman wrote:
> On Tue, Jul 14, 2015 at 08:09:10AM +0800, Fengguang Wu wrote:
> > Greetings,
> > 
> > 0day kernel testing robot got the below dmesg and the first bad commit is
> > 
> > git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > 
> 
> Can you check if this patch addresses the problem please?

It works!

Tested-by: Fengguang Wu <fengguang.wu@...el.com>

Thanks,
Fengguang

> ---8<---
> mm, meminit: replace rwsem with completion
> 
> From: Nicolai Stange <nicstange@...il.com>
> 
> 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: [<ffffffff8424c7fb>] page_alloc_init_late+0xc7/0xe6
> 
>   but task is already holding lock:
>   (pgdat_init_rwsem){++++.+},
>     at: [<ffffffff8424c772>] page_alloc_init_late+0x3e/0xe6
> 
> Replace the rwsem by a completion together with an atomic
> "outstanding work counter".
> 
> [peterz@...radead.org: Barrier removal on the grounds of being pointless]
> [mgorman@...e.de: Applied review feedback]
> Signed-off-by: Nicolai Stange <nicstange@...il.com>
> Signed-off-by: Mel Gorman <mgorman@...e.de>
> ---
>  mm/page_alloc.c | 22 +++++++++++++++-------
>  1 file changed, 15 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 506eac8b38af..a69e78c396a0 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -18,7 +18,6 @@
>  #include <linux/mm.h>
>  #include <linux/swap.h>
>  #include <linux/interrupt.h>
> -#include <linux/rwsem.h>
>  #include <linux/pagemap.h>
>  #include <linux/jiffies.h>
>  #include <linux/bootmem.h>
> @@ -1062,7 +1061,15 @@ static void __init deferred_free_range(struct page *page,
>  		__free_pages_boot_core(page, pfn, 0);
>  }
>  
> -static __initdata DECLARE_RWSEM(pgdat_init_rwsem);
> +/* Completion tracking for 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)
> +{
> +	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 +1086,7 @@ 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 +1186,8 @@ 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 +1195,14 @@ 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);
>  }
>  #endif /* CONFIG_DEFERRED_STRUCT_PAGE_INIT */
>  
--
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