On Fri, Nov 25, 2016 at 01:58:57PM +0100, Vlastimil Babka wrote:
> On 11/25/2016 12:41 PM, Andrey Ryabinin wrote:
> >
> >
> > On 11/25/2016 11:42 AM, Vlastimil Babka wrote:
> >
> >> pr_emerg("page:%p count:%d mapcount:%d mapping:%p index:%#lx",
> >> page, page_ref_count(page), mapcount,
> >> @@ -59,6 +61,21 @@ void __dump_page(struct page *page, const char *reason)
> >>
> >> pr_emerg("flags: %#lx(%pGp)\n", page->flags, &page->flags);
> >>
> >> + pr_alert("raw struct page data:");
> >> + for (i = 0; i < sizeof(struct page) / sizeof(unsigned long); i++) {
> >> + unsigned long *word_ptr;
> >> +
> >> + word_ptr = ((unsigned long *) page) + i;
> >> +
> >> + if ((i % words_per_line) == 0) {
> >> + pr_cont("\n");
> >> + pr_alert(" %016lx", *word_ptr);
> >> + } else {
> >> + pr_cont(" %016lx", *word_ptr);
> >> + }
> >> + }
> >> + pr_cont("\n");
> >> +
> >
> > Single call to print_hex_dump() could replace this loop.
>
> Ah, didn't know about that one, thanks!
>
> This also addresses Kirill's comment:
>
> -----8<-----
> From 417467521d0a68fb70dc2d5bd151524bf0c79437 Mon Sep 17 00:00:00 2001
> From: Vlastimil Babka <vbabka@xxxxxxx>
> Date: Fri, 25 Nov 2016 09:08:05 +0100
> Subject: [PATCH] mm, debug: print raw struct page data in __dump_page()
>
> The __dump_page() function is used when a page metadata inconsistency is
> detected, either by standard runtime checks, or extra checks in CONFIG_DEBUG_VM
> builds. It prints some of the relevant metadata, but not the whole struct page,
> which is based on unions and interpretation is dependent on the context.
>
> This means that sometimes e.g. a VM_BUG_ON_PAGE() checks certain field, which
> is however not printed by __dump_page() and the resulting bug report may then
> lack clues that could help in determining the root cause. This patch solves
> the problem by simply printing the whole struct page word by word, so no part
> is missing, but the interpretation of the data is left to developers. This is
> similar to e.g. x86_64 raw stack dumps.
>
> Example output:
>
> page:ffffea00000475c0 count:1 mapcount:0 mapping: (null) index:0x0
> flags: 0x100000000000400(reserved)
> raw: 0100000000000400 0000000000000000 0000000000000000 00000001ffffffff
> raw: ffffea00000475e0 ffffea00000475e0 0000000000000000 0000000000000000
> page dumped because: VM_BUG_ON_PAGE(1)
>
> [aryabinin@xxxxxxxxxxxxx: suggested print_hex_dump()]
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---
> mm/debug.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/mm/debug.c b/mm/debug.c
> index 9feb699c5d25..185c19bda078 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -59,6 +59,10 @@ void __dump_page(struct page *page, const char *reason)
>
> pr_emerg("flags: %#lx(%pGp)\n", page->flags, &page->flags);
>
> + print_hex_dump(KERN_ALERT, "raw: ", DUMP_PREFIX_NONE,
> + 32, (sizeof(unsigned long) == 8) ? 8 : 4,
That's a very fancy way to write sizeof(unsigned long) ;)
--
Kirill A. Shutemov
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