linux-kernel - Re: [PATCH] mm, debug: always print flags in dump

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Message-ID: <20200114133520.GO19428@dhcp22.suse.cz>
Date:   Tue, 14 Jan 2020 14:35:20 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        David Hildenbrand <david@...hat.com>, Qian Cai <cai@....pw>,
        Oscar Salvador <osalvador@...e.de>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Pavel Tatashin <pavel.tatashin@...rosoft.com>,
        linux-kernel@...r.kernel.org, Ralph Campbell <rcampbell@...dia.com>
Subject: Re: [PATCH] mm, debug: always print flags in dump_page()

On Tue 14-01-20 13:04:31, Vlastimil Babka wrote:
[...]
> >From 7b673c45bc16526586ae8ea6fba416a547baa04e Mon Sep 17 00:00:00 2001
> From: Vlastimil Babka <vbabka@...e.cz>
> Date: Tue, 14 Jan 2020 12:52:48 +0100
> Subject: [PATCH] mm, debug: always print flags in dump_page()
> 
> Commit 76a1850e4572 ("mm/debug.c: __dump_page() prints an extra line")
> inadvertently removed printing of page flags for pages that are neither
> anon nor ksm nor have a mapping. Fix that.
> 
> Using pr_cont() again would be a solution, but the commit explicitly removed
> its use. Avoiding the danger of mixing up split lines from multiple CPUs might
> be beneficial for near-panic dumps like this, so fix this without reintroducing
> pr_cont().
> 
> Reported-by: Anshuman Khandual <anshuman.khandual@....com>
> Reported-by: Michal Hocko <mhocko@...nel.org>
> Fixes: 76a1850e4572 ("mm/debug.c: __dump_page() prints an extra line")
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>

Acked-by: Michal Hocko <mhocko@...e.com>

Thanks!

> ---
>  mm/debug.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/debug.c b/mm/debug.c
> index 0461df1207cb..6a52316af839 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -47,6 +47,7 @@ void __dump_page(struct page *page, const char *reason)
>  	struct address_space *mapping;
>  	bool page_poisoned = PagePoisoned(page);
>  	int mapcount;
> +	char *type = "";
>  
>  	/*
>  	 * If struct page is poisoned don't access Page*() functions as that
> @@ -78,9 +79,9 @@ void __dump_page(struct page *page, const char *reason)
>  			page, page_ref_count(page), mapcount,
>  			page->mapping, page_to_pgoff(page));
>  	if (PageKsm(page))
> -		pr_warn("ksm flags: %#lx(%pGp)\n", page->flags, &page->flags);
> +		type = "ksm ";
>  	else if (PageAnon(page))
> -		pr_warn("anon flags: %#lx(%pGp)\n", page->flags, &page->flags);
> +		type = "anon ";
>  	else if (mapping) {
>  		if (mapping->host && mapping->host->i_dentry.first) {
>  			struct dentry *dentry;
> @@ -88,10 +89,11 @@ void __dump_page(struct page *page, const char *reason)
>  			pr_warn("%ps name:\"%pd\"\n", mapping->a_ops, dentry);
>  		} else
>  			pr_warn("%ps\n", mapping->a_ops);
> -		pr_warn("flags: %#lx(%pGp)\n", page->flags, &page->flags);
>  	}
>  	BUILD_BUG_ON(ARRAY_SIZE(pageflag_names) != __NR_PAGEFLAGS + 1);
>  
> +	pr_warn("%sflags: %#lx(%pGp)\n", type, page->flags, &page->flags);
> +
>  hex_only:
>  	print_hex_dump(KERN_WARNING, "raw: ", DUMP_PREFIX_NONE, 32,
>  			sizeof(unsigned long), page,
> -- 
> 2.24.1

-- 
Michal Hocko
SUSE Labs