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Tue, 10 Nov 2026 15:37:36 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id eyAkLEA682qaawAAD6G6ig (envelope-from ); Tue, 10 Nov 2026 15:37:36 +0000 Date: Tue, 10 Nov 2026 15:37:35 +0000 From: Pedro Falcato To: "Lorenzo Stoakes (ARM)" Cc: Andrew Morton , Suren Baghdasaryan , "Liam R. Howlett" , Vlastimil Babka , Shakeel Butt , Jann Horn , Lance Yang , "David Hildenbrand (Arm)" , "Kiryl Shutsemau (Meta)" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Seunghyun An Subject: Re: [PATCH] mm/vma: predicate vma_assert_stabilised() on CONFIG_DEBUG_VM Message-ID: References: <20261110-vma-fixup-debug-asserts-v1-1-0b2e0680cd7e@kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261110-vma-fixup-debug-asserts-v1-1-0b2e0680cd7e@kernel.org> X-Spam-Flag: NO X-Spam-Level: X-Spamd-Result: default: False [-13.30 / 50.00]; SUSE_INTERNAL_BYPASS(-9.00)[]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; MISSING_XM_UA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[13]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.de:email,wisc.edu:email] X-Spam-Score: -13.30 On Tue, Nov 10, 2026 at 03:10:40PM +0000, Lorenzo Stoakes (ARM) wrote: > I introduced commit 17fd82c3abe0 ("mm/vma: add and use > vma_assert_stabilised()") with the intent of picking up programmatic bugs > when debugging mm code, but kept the general practice of asserting even > when CONFIG_DEBUG_VM is not set in line with existing code. > > However, it turns out doing so can cause performance regressions, > especially when asserted in vma_has_anon_rmap() which is referenced in a > number of hotpaths. > > Since the intent was always a debug-only assertion, explicitly check for > CONFIG_DEBUG_VM and do not assert if it isn't set. > > Really all of the assert paths need to be predicated on this, but start > with this one only, out of caution. > > Additionally, since a detached VMA is trivially stabilised (nothing to > stabilise against), check for this case at the outset, and update > vma_has_anon_rmap() to not explicitly need to check for this. > > This also, importantly, avoids reading any VMA fields if CONFIG_DEBUG_VM is > not set. > > Target the commit which introduced vma_has_anon_rmap() for the fix, as this > is where the issue started manifesting in practice. > > Fixes: 38564710f443 ("mm: implement and use vma_has_anon_rmap(), silence KCSAN") > Reported-by: Seunghyun An > Closes: https://lore.kernel.org/linux-mm/20261110000002.1834454-1-san55@wisc.edu/ > Signed-off-by: Lorenzo Stoakes (ARM) Reviewed-by: Pedro Falcato -- Pedro