linux-kernel - Re: [PATCH] mm: dump page when hitting a VM_BUG_ON using VM_BUG_ON

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Date:	Fri, 27 Dec 2013 12:38:47 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: dump page when hitting a VM_BUG_ON using
 VM_BUG_ON_PAGE

On Thu, Dec 26, 2013 at 10:20:52PM -0500, Sasha Levin wrote:
> Most of the VM_BUG_ON assertions are performed on a page. Usually, when
> one of these assertions fails we'll get a BUG_ON with a call stack and
> the registers.
> 
> I've recently noticed based on the requests to add a small piece of code
> that dumps the page to various VM_BUG_ON sites that the page dump is quite
> useful to people debugging issues in mm.
> 
> This patch adds a VM_BUG_ON_PAGE(cond, page) which beyond doing what
> VM_BUG_ON() does, also dumps the page before executing the actual BUG_ON.
> 
> Signed-off-by: Sasha Levin <sasha.levin@...cle.com>

I like the idea. One thing I've noticed you have a lot of page flag based
asserts, like:

	VM_BUG_ON_PAGE(PageLRU(page), page);
	VM_BUG_ON_PAGE(!PageLocked(page), page);

What about adding per-page-flag assert macros, like:

	PageNotLRU_assert(page);
	PageLocked_assert(page);

? This way we will always dump right page on bug.

-- 
 Kirill A. Shutemov
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