From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Sasha Levin <sasha.levin@oracle.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: __delete_from_page_cache show Bad page if mapped
Date: Tue, 1 Mar 2016 14:16:56 +0300 [thread overview]
Message-ID: <20160301111656.GA19095@node.shutemov.name> (raw)
In-Reply-To: <alpine.LSU.2.11.1602292244320.7377@eggly.anvils>
On Mon, Feb 29, 2016 at 10:45:59PM -0800, Hugh Dickins wrote:
> Commit e1534ae95004 ("mm: differentiate page_mapped() from page_mapcount()
> for compound pages") changed the famous BUG_ON(page_mapped(page)) in
> __delete_from_page_cache() to VM_BUG_ON_PAGE(page_mapped(page)): which
> gives us more info when CONFIG_DEBUG_VM=y, but nothing at all when not.
>
> Although it has not usually been very helpul, being hit long after the
> error in question, we do need to know if it actually happens on users'
> systems; but reinstating a crash there is likely to be opposed :)
>
> In the non-debug case, pr_alert("BUG: Bad page cache") plus dump_page(),
> dump_stack(), add_taint() - I don't really believe LOCKDEP_NOW_UNRELIABLE,
> but that seems to be the standard procedure now. Move that, or the
> VM_BUG_ON_PAGE(), up before the deletion from tree: so that the
> unNULLified page->mapping gives a little more information.
>
> If the inode is being evicted (rather than truncated), it won't have
> any vmas left, so it's safe(ish) to assume that the raised mapcount is
> erroneous, and we can discount it from page_count to avoid leaking the
> page (I'm less worried by leaking the occasional 4kB, than losing a
> potential 2MB page with each 4kB page leaked).
>
> Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
--
Kirill A. Shutemov
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next prev parent reply other threads:[~2016-03-01 11:16 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-29 4:49 [PATCH] mm: __delete_from_page_cache WARN_ON(page_mapped) Hugh Dickins
2016-02-29 7:44 ` Joonsoo Kim
2016-02-29 9:52 ` Kirill A. Shutemov
2016-03-01 6:43 ` Hugh Dickins
2016-03-01 6:45 ` [PATCH] mm: __delete_from_page_cache show Bad page if mapped Hugh Dickins
2016-03-01 11:16 ` Kirill A. Shutemov [this message]
2016-04-18 15:06 ` Sasha Levin
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