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[2003:d8:2f27:6d00:7b96:afc9:83d0:5bd]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46139122cb5sm36693815e9.8.2025.09.17.06.44.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 17 Sep 2025 06:44:29 -0700 (PDT) Message-ID: Date: Wed, 17 Sep 2025 15:44:27 +0200 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 6/7] mm: add assertion for VMA count limit To: Kalesh Singh , akpm@linux-foundation.org, minchan@kernel.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, rppt@kernel.org, pfalcato@suse.de Cc: kernel-team@android.com, android-mm@google.com, Alexander Viro , Christian Brauner , Jan Kara , Kees Cook , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , Valentin Schneider , Jann Horn , Shuah Khan , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org References: <20250915163838.631445-1-kaleshsingh@google.com> <20250915163838.631445-7-kaleshsingh@google.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 15.09.25 18:36, Kalesh Singh wrote: > Building on the vma_count helpers, add a VM_WARN_ON_ONCE() to detect > cases where the VMA count exceeds the sysctl_max_map_count limit. > > This check will help catch future bugs or regressions where > the VMAs are allocated exceeding the limit. > > The warning is placed in the main vma_count_*() helpers, while the > internal *_nocheck variants bypass it. _nocheck helpers are used to > ensure that the assertion does not trigger a false positive in > the legitimate case of a temporary VMA increase past the limit > by a VMA split in munmap(). > > Cc: Andrew Morton > Cc: David Hildenbrand > Cc: "Liam R. Howlett" > Cc: Lorenzo Stoakes > Cc: Mike Rapoport > Cc: Minchan Kim > Cc: Pedro Falcato > Signed-off-by: Kalesh Singh > --- > > Changes in v2: > - Add assertions if exceeding max_vma_count limit, per Pedro > > include/linux/mm.h | 12 ++++++-- > mm/internal.h | 1 - > mm/vma.c | 49 +++++++++++++++++++++++++------- > tools/testing/vma/vma_internal.h | 7 ++++- > 4 files changed, 55 insertions(+), 14 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 8bad1454984c..3a3749d7015c 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -4219,19 +4219,27 @@ static inline bool snapshot_page_is_faithful(const struct page_snapshot *ps) > > void snapshot_page(struct page_snapshot *ps, const struct page *page); > > +int vma_count_remaining(const struct mm_struct *mm); > + > static inline void vma_count_init(struct mm_struct *mm) > { > ACCESS_PRIVATE(mm, __vma_count) = 0; > } > > -static inline void vma_count_add(struct mm_struct *mm, int nr_vmas) > +static inline void __vma_count_add_nocheck(struct mm_struct *mm, int nr_vmas) > { > ACCESS_PRIVATE(mm, __vma_count) += nr_vmas; > } > > +static inline void vma_count_add(struct mm_struct *mm, int nr_vmas) > +{ > + VM_WARN_ON_ONCE(!vma_count_remaining(mm)); Can't that fire when changing the max count from user space at just the wrong time? I assume we'll have to tolerated that and might just want to drop this patch from the series. -- Cheers David / dhildenb