linux-kernel - Re: [PATCH -next] mm/hotplug: silence a lockdep splat with printk()

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Message-ID: <6d9d2923-a44c-60fb-5caa-e6228cb8aaf5@redhat.com>
Date:   Tue, 14 Jan 2020 21:20:08 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Qian Cai <cai@....pw>, akpm@...ux-foundation.org
Cc:     mhocko@...nel.org, sergey.senozhatsky.work@...il.com,
        pmladek@...e.com, rostedt@...dmis.org, peterz@...radead.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] mm/hotplug: silence a lockdep splat with printk()

On 14.01.20 21:11, Qian Cai wrote:
> Similar to the recent commit [1] merged into the random and -next trees,
> it is not a good idea to call printk() with zone->lock held. The
> standard fix is to use printk_deferred() in those places, but memory
> offline will call dump_page() which need to defer after the lock. While
> at it, remove a similar but unnecessary debug printk() as well.
> 
> [1] https://lore.kernel.org/lkml/1573679785-21068-1-git-send-email-cai@lca.pw/
> 
> Signed-off-by: Qian Cai <cai@....pw>
> ---
>  include/linux/page-isolation.h |  2 +-
>  mm/memory_hotplug.c            |  2 +-
>  mm/page_alloc.c                | 12 +++++-------
>  mm/page_isolation.c            | 10 +++++++++-
>  4 files changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
> index 148e65a9c606..5d8ba078006f 100644
> --- a/include/linux/page-isolation.h
> +++ b/include/linux/page-isolation.h
> @@ -34,7 +34,7 @@ static inline bool is_migrate_isolate(int migratetype)
>  #define REPORT_FAILURE	0x2
>  
>  bool has_unmovable_pages(struct zone *zone, struct page *page, int migratetype,
> -			 int flags);
> +			 int flags, char *dump);
>  void set_pageblock_migratetype(struct page *page, int migratetype);
>  int move_freepages_block(struct zone *zone, struct page *page,
>  				int migratetype, int *num_movable);
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 7a6de9b0dcab..f10928538fa3 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1149,7 +1149,7 @@ static bool is_pageblock_removable_nolock(unsigned long pfn)
>  		return false;
>  
>  	return !has_unmovable_pages(zone, page, MIGRATE_MOVABLE,
> -				    MEMORY_OFFLINE);
> +				    MEMORY_OFFLINE, NULL);
>  }
>  
>  /* Checks if this range of memory is likely to be hot-removable. */
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index e56cd1f33242..b6bec3925e80 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8204,7 +8204,7 @@ void *__init alloc_large_system_hash(const char *tablename,
>   * race condition. So you can't expect this function should be exact.
>   */
>  bool has_unmovable_pages(struct zone *zone, struct page *page, int migratetype,
> -			 int flags)
> +			 int flags, char *dump)
>  {
>  	unsigned long iter = 0;
>  	unsigned long pfn = page_to_pfn(page);
> @@ -8305,8 +8305,10 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int migratetype,
>  	return false;
>  unmovable:
>  	WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE);
> -	if (flags & REPORT_FAILURE)
> -		dump_page(pfn_to_page(pfn + iter), reason);
> +	if (flags & REPORT_FAILURE) {
> +		page = pfn_to_page(pfn + iter);
> +		strscpy(dump, reason, 64);
> +	}
>  	return true;
>  }
>  
> @@ -8711,10 +8713,6 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
>  		BUG_ON(!PageBuddy(page));
>  		order = page_order(page);
>  		offlined_pages += 1 << order;
> -#ifdef CONFIG_DEBUG_VM
> -		pr_info("remove from free list %lx %d %lx\n",
> -			pfn, 1 << order, end_pfn);
> -#endif

ack to getting rid of this.

Regarding the other stuff, I remember Michal had an opinion about the
previous approach, so it's best if he comments.

-- 
Thanks,

David / dhildenb