From: Matthew Wilcox <willy@infradead.org>
To: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-m68k@lists.linux-m68k.org, anshuman.khandual@arm.com,
akpm@linux-foundation.org, william.kucharski@oracle.com,
mike.kravetz@oracle.com, vbabka@suse.cz, geert@linux-m68k.org,
schmitzmic@gmail.com, rostedt@goodmis.org, mingo@redhat.com,
hannes@cmpxchg.org, guro@fb.com, songmuchun@bytedance.com,
weixugc@google.com, gthelen@google.com
Subject: Re: [RFC 0/8] Hardening page _refcount
Date: Tue, 26 Oct 2021 19:23:39 +0100 [thread overview]
Message-ID: <YXhHq52jDrU61V4E@casper.infradead.org> (raw)
In-Reply-To: <20211026173822.502506-1-pasha.tatashin@soleen.com>
On Tue, Oct 26, 2021 at 05:38:14PM +0000, Pasha Tatashin wrote:
> It is hard to root cause _refcount problems, because they usually
> manifest after the damage has occurred. Yet, they can lead to
> catastrophic failures such memory corruptions.
>
> Improve debugability by adding more checks that ensure that
> page->_refcount never turns negative (i.e. double free does not
> happen, or free after freeze etc).
>
> - Check for overflow and underflow right from the functions that
> modify _refcount
> - Remove set_page_count(), so we do not unconditionally overwrite
> _refcount with an unrestrained value
> - Trace return values in all functions that modify _refcount
I think this is overkill. Won't we get exactly the same protection
by simply testing that page->_refcount == 0 in set_page_count()?
Anything which triggers that BUG_ON would already be buggy because
it can race with speculative gets.
next prev parent reply other threads:[~2021-10-26 18:24 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-26 17:38 Pasha Tatashin
2021-10-26 17:38 ` [RFC 1/8] mm: add overflow and underflow checks for page->_refcount Pasha Tatashin
2021-10-26 19:48 ` Matthew Wilcox
2021-10-26 21:34 ` Pasha Tatashin
2021-10-27 1:21 ` Pasha Tatashin
2021-10-27 3:04 ` Matthew Wilcox
2021-10-27 18:22 ` Pasha Tatashin
2021-10-27 7:46 ` Muchun Song
2021-10-27 18:22 ` Pasha Tatashin
2021-10-28 4:08 ` Muchun Song
2021-10-26 17:38 ` [RFC 2/8] mm/hugetlb: remove useless set_page_count() Pasha Tatashin
2021-10-26 18:44 ` Mike Kravetz
2021-10-26 18:50 ` Pasha Tatashin
2021-10-26 21:19 ` Mike Kravetz
2021-10-26 17:38 ` [RFC 3/8] mm: Avoid using set_page_count() in set_page_recounted() Pasha Tatashin
2021-10-26 17:53 ` John Hubbard
2021-10-26 18:01 ` John Hubbard
2021-10-26 18:14 ` Pasha Tatashin
2021-10-26 18:21 ` Pasha Tatashin
2021-10-27 5:12 ` John Hubbard
2021-10-27 18:27 ` Pasha Tatashin
2021-10-28 1:20 ` John Hubbard
2021-10-28 1:35 ` John Hubbard
2021-11-01 14:30 ` Pasha Tatashin
2021-11-01 19:35 ` John Hubbard
2021-11-01 14:22 ` Pasha Tatashin
2021-11-01 19:31 ` John Hubbard
2021-11-01 19:42 ` John Hubbard
2021-10-26 17:38 ` [RFC 4/8] mm: remove set_page_count() from page_frag_alloc_align Pasha Tatashin
2021-10-26 17:38 ` [RFC 5/8] mm: avoid using set_page_count() when pages are freed into allocator Pasha Tatashin
2021-10-26 17:38 ` [RFC 6/8] mm: rename init_page_count() -> page_ref_init() Pasha Tatashin
2021-10-27 6:46 ` Geert Uytterhoeven
2021-10-26 17:38 ` [RFC 7/8] mm: remove set_page_count() Pasha Tatashin
2021-10-26 17:38 ` [RFC 8/8] mm: simplify page_ref_* functions Pasha Tatashin
2021-10-26 18:23 ` Matthew Wilcox [this message]
2021-10-26 18:30 ` [RFC 0/8] Hardening page _refcount Pasha Tatashin
2021-10-26 20:13 ` Matthew Wilcox
2021-10-26 21:24 ` Pasha Tatashin
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