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From: Michal Hocko <mhocko@suse.com>
To: Suren Baghdasaryan <surenb@google.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
	"Colin Cross" <ccross@google.com>,
	"Sumit Semwal" <sumit.semwal@linaro.org>,
	"Dave Hansen" <dave.hansen@intel.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Matthew Wilcox" <willy@infradead.org>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	"Vlastimil Babka" <vbabka@suse.cz>,
	"Johannes Weiner" <hannes@cmpxchg.org>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Randy Dunlap" <rdunlap@infradead.org>,
	"Kalesh Singh" <kaleshsingh@google.com>,
	"Peter Xu" <peterx@redhat.com>,
	rppt@kernel.org, "Peter Zijlstra" <peterz@infradead.org>,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	vincenzo.frascino@arm.com,
	"Chinwen Chang (張錦文)" <chinwen.chang@mediatek.com>,
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	"Jann Horn" <jannh@google.com>,
	apopple@nvidia.com, "John Hubbard" <jhubbard@nvidia.com>,
	"Yu Zhao" <yuzhao@google.com>, "Will Deacon" <will@kernel.org>,
	fenghua.yu@intel.com, thunder.leizhen@huawei.com,
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	legion@kernel.org, "Rolf Eike Beer" <eb@emlix.com>,
	"Muchun Song" <songmuchun@bytedance.com>,
	"Viresh Kumar" <viresh.kumar@linaro.org>,
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	sashal@kernel.org, cxfcosmos@gmail.com,
	"Rasmus Villemoes" <linux@rasmusvillemoes.dk>,
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	linux-mm <linux-mm@kvack.org>,
	kernel-team <kernel-team@android.com>
Subject: Re: [PATCH v8 2/3] mm: add a field to store names for private anonymous memory
Date: Fri, 3 Sep 2021 13:49:01 +0200	[thread overview]
Message-ID: <YTILrVHLMBky9YjP@dhcp22.suse.cz> (raw)
In-Reply-To: <CAJuCfpHWCtqCcuZdyfc4-virtynOMv2f_iU=OJUB_6b2Xz+k9g@mail.gmail.com>

On Wed 01-09-21 08:42:29, Suren Baghdasaryan wrote:
> On Wed, Sep 1, 2021 at 1:10 AM 'Michal Hocko' via kernel-team
> <kernel-team@android.com> wrote:
> >
> > On Fri 27-08-21 12:18:57, Suren Baghdasaryan wrote:
> > [...]
> > > +static void replace_vma_anon_name(struct vm_area_struct *vma, const char *name)
> > > +{
> > > +     if (!name) {
> > > +             free_vma_anon_name(vma);
> > > +             return;
> > > +     }
> > > +
> > > +     if (vma->anon_name) {
> > > +             /* Should never happen, to dup use dup_vma_anon_name() */
> > > +             WARN_ON(vma->anon_name == name);
> >
> > What is the point of this warning?
> 
> I wanted to make sure replace_vma_anon_name() is not used from inside
> vm_area_dup() or some similar place (does not exist today but maybe in
> the future) where "new" vma is a copy of "orig" vma and
> new->anon_name==orig->anon_name. If someone by mistake calls
> replace_vma_anon_name(new, orig->anon_name) and
> new->anon_name==orig->anon_name then they will keep pointing to the
> same name pointer, which breaks an assumption that ->anon_name
> pointers are not shared among vmas even if the string is the same.
> That would eventually lead to use-after-free error. After the next
> patch implementing refcounting, the similar situation would lead to
> both new and orig vma pointing to the same anon_vma_name structure
> without raising the refcount, which would also lead to use-after-free
> error. That's why the above comment asks to use dup_vma_anon_name() if
> this warning ever happens.
> I can remove the warning but I thought the problem is subtle enough to
> put some safeguards.

This to me sounds very much like a debugging code that shouldn't make it
to the final patch to be merged. I do see your point of an early
diagnostic but we are talking about an internal MM code and that is not
really designed to be robust against its own failures so I do not see
why this should be any special.
-- 
Michal Hocko
SUSE Labs

  reply	other threads:[~2021-09-03 11:49 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-27 19:18 [PATCH v8 0/3] Anonymous VMA naming patches Suren Baghdasaryan
2021-08-27 19:18 ` [PATCH v8 1/3] mm: rearrange madvise code to allow for reuse Suren Baghdasaryan
2021-08-28  0:14   ` Kees Cook
2021-08-28  0:58     ` Suren Baghdasaryan
2021-08-28 16:19   ` Cyrill Gorcunov
2021-08-28 21:59     ` Suren Baghdasaryan
2021-08-27 19:18 ` [PATCH v8 2/3] mm: add a field to store names for private anonymous memory Suren Baghdasaryan
2021-08-28  1:47   ` Matthew Wilcox
2021-08-28  5:52     ` Kees Cook
2021-08-28 21:47       ` Suren Baghdasaryan
2021-08-30  8:12         ` Rasmus Villemoes
2021-08-30 16:16           ` Suren Baghdasaryan
2021-08-30 16:59             ` Matthew Wilcox
2021-08-31 17:21               ` Suren Baghdasaryan
2021-08-28 21:28   ` Cyrill Gorcunov
2021-08-28 21:53     ` Suren Baghdasaryan
2021-09-01  8:09   ` Michal Hocko
2021-09-01 15:28     ` Suren Baghdasaryan
2021-09-01  8:10   ` Michal Hocko
2021-09-01 15:42     ` Suren Baghdasaryan
2021-09-03 11:49       ` Michal Hocko [this message]
2021-09-03 15:47         ` Suren Baghdasaryan
2021-08-27 19:18 ` [PATCH v8 3/3] mm: add anonymous vma name refcounting Suren Baghdasaryan
2021-08-28  5:28   ` Kees Cook
2021-08-28 21:13     ` Suren Baghdasaryan
2021-08-30  7:03   ` Rolf Eike Beer
2021-08-30 16:12     ` Suren Baghdasaryan
2021-08-28 12:48 ` [PATCH v8 0/3] Anonymous VMA naming patches Pavel Machek
2021-08-28 22:06   ` Suren Baghdasaryan

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