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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> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: iysef79ecfwbsxhhjfddk4egqiep4dq9 X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 504CA4000C X-HE-Tag: 1782829550-844366 X-HE-Meta: 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 7e687ort 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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