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[95.25.158.125]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5aebe4985eesm629795e87.46.2026.06.30.07.25.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 30 Jun 2026 07:25:47 -0700 (PDT) From: Igor Putko To: sj@kernel.org Cc: damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/damon/vaddr: remove redundant RCU lock Date: Tue, 30 Jun 2026 17:25:22 +0300 Message-ID: <20260630102400.reply-damon@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260629165349.4260-1-igorpetindev@gmail.com> References: <20260629165349.4260-1-igorpetindev@gmail.com> Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Hi SJ, Thanks for the reply and the pointers! Regarding the issue Sashiko AI flagged - I dug into damon/vaddr.c, and I think it's a real bug, but it's isolated to __damon_va_three_regions(). damon_va_walk_page_range() is fine here, since lock_vma_under_rcu() handles stability on its own. __damon_va_three_regions() is the problematic one: right after mmap_read_lock(mm) is taken in the caller, it sets up a VMA_ITERATOR and runs for_each_vma(). But mmap_read_lock doesn't stop the OOM reaper from running concurrently, setting MMF_UNSTABLE, and leaving empty markers in the maple tree. Walking the tree in that state without a check_stable_address_space(mm) call could lead to a NULL pointer dereference. Since this looks like a separate issue, I'll prepare a dedicated fix and send it as its own patch thread, so it doesn't hold up the current cleanup. Let me know if that approach works for you. Thanks, Igor