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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	sumit.semwal@linaro.org,  Sasha Levin <sashal@kernel.org>,
	Peter Collingbourne <pcc@google.com>,
	Michal Hocko <mhocko@suse.com>,
	 Alexey Gladkov <legion@kernel.org>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	 Kees Cook <keescook@chromium.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	 Cyrill Gorcunov <gorcunov@gmail.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	 David Hildenbrand <david@redhat.com>,
	Davidlohr Bueso <dave@stgolabs.net>,
	 Dave Hansen <dave.hansen@intel.com>,
	chris.hyser@oracle.com,  Colin Cross <ccross@google.com>,
	caoxiaofeng@yulong.com,  Christian Brauner <brauner@kernel.org>,
	Suren Baghdasaryan <surenb@google.com>,
	patches@lists.linux.dev,  Linux-MM <linux-mm@kvack.org>,
	mm-commits@vger.kernel.org
Subject: Re: [patch 3/8] mm: prevent vm_area_struct::anon_name refcount saturation
Date: Sat, 5 Mar 2022 11:03:36 -0800	[thread overview]
Message-ID: <CAHk-=wjA82m5VxsjXLN7giO--0rqXq7-WXxy+O2UTjtdYdYZ3g@mail.gmail.com> (raw)
In-Reply-To: <20220305042855.BFBB9C004E1@smtp.kernel.org>

On Fri, Mar 4, 2022 at 8:28 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> To ensure anon_vma_name refcount does not overflow, stop anon_vma_name
> sharing when the refcount reaches REFCOUNT_MAX (2147483647), which still
> leaves INT_MAX/2 (1073741823) values before the counter reaches
> REFCOUNT_SATURATED.  This should provide enough headroom for raising the
> refcounts temporarily.

This is a classic case of kref simply being the wrong type for this.

We sh ould move away from that idiotic "saturate with a warning" type,
and just codify that what the page refs do is the RightThing(tm) to
do.

I've ranted against kref for years, I hate that damn thing. It's
literally broken by design with the known leaking behavior.

Oh well. I'm taking this patch as a "fix up refcount problems", and I
guess I need to some day just extract the page_ref code into a nice
type of its own so that it's usable outside of pages.

(Others have copied the page_ref code manually, but there's no "helper
type with functions to use it", which is why people then use that
mis-designed refcount stuff).

              Linus

  reply	other threads:[~2022-03-05 19:04 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-05  4:28 incoming Andrew Morton
2022-03-05  4:28 ` [patch 1/8] selftests/vm: cleanup hugetlb file after mremap test Andrew Morton
2022-03-05  4:28   ` Andrew Morton
2022-03-05  4:28 ` [patch 2/8] mm: refactor vm_area_struct::anon_vma_name usage code Andrew Morton
2022-03-05  4:28   ` Andrew Morton
2022-03-05  4:28 ` [patch 3/8] mm: prevent vm_area_struct::anon_name refcount saturation Andrew Morton
2022-03-05  4:28   ` Andrew Morton
2022-03-05 19:03   ` Linus Torvalds [this message]
2022-03-05  4:28 ` [patch 4/8] mm: fix use-after-free when anon vma name is used after vma is freed Andrew Morton
2022-03-05  4:28   ` Andrew Morton
2022-03-05  4:29 ` [patch 5/8] memfd: fix F_SEAL_WRITE after shmem huge page allocated Andrew Morton
2022-03-05  4:29   ` Andrew Morton
2022-03-05  4:29 ` [patch 6/8] kselftest/vm: fix tests build with old libc Andrew Morton
2022-03-05  4:29   ` Andrew Morton
2022-03-05  4:29 ` [patch 7/8] proc: fix documentation and description of pagemap Andrew Morton
2022-03-05  4:29   ` Andrew Morton
2022-03-05  4:29 ` [patch 8/8] configs/debug: set CONFIG_DEBUG_INFO=y properly Andrew Morton
2022-03-05  4:29   ` Andrew Morton

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