linux-kernel - Re: [v4 PATCH 1/2] mm: thp: replace DEBUG_VM BUG with VM

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Date:   Thu, 27 May 2021 13:52:14 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Yang Shi <shy828301@...il.com>
Cc:     hughd@...gle.com, ziy@...dia.com, kirill.shutemov@...ux.intel.com,
        minchan@...nel.org, naoya.horiguchi@....com,
        wangyugui@...-tech.com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [v4 PATCH 1/2] mm: thp: replace DEBUG_VM BUG with VM_WARN when
 unmap fails for split

On Wed, May 26, 2021 at 01:12:38PM -0700, Yang Shi wrote:
> When debugging the bug reported by Wang Yugui [1], try_to_unmap() may
> fail, but the first VM_BUG_ON_PAGE() just checks page_mapcount() however
> it may miss the failure when head page is unmapped but other subpage is
> mapped.  Then the second DEBUG_VM BUG() that check total mapcount would
> catch it.  This may incur some confusion.  And this is not a fatal issue,
> so consolidate the two DEBUG_VM checks into one VM_WARN_ON_ONCE_PAGE().
> 
> [1] https://lore.kernel.org/linux-mm/20210412180659.B9E3.409509F4@e16-tech.com/
> 
> Reviewed-by: Zi Yan <ziy@...dia.com>
> Signed-off-by: Yang Shi <shy828301@...il.com>

For both patches: 

Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
 Kirill A. Shutemov