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McKenney" , Peter Zijlstra , damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, zouyipeng@huawei.com, Hugh Dickins Subject: Re: [BUG REPORT] mm/damon: softlockup when kdamond walk page with cpu hotplug Date: Thu, 18 Sep 2025 01:57:00 -0700 Message-Id: <20250918085701.59085-1-sj@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250918085249.58966-1-sj@kernel.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: p1b7eat1x6je6ibgkx6co6miuu3jbics X-Rspam-User: X-Rspamd-Queue-Id: 2B5C3A0007 X-Rspamd-Server: rspam10 X-HE-Tag: 1758185824-342773 X-HE-Meta: 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 uFZdp8yj ThRrZgHVvX8j842EuJrqbktHqobrTsHH7WyPw7wdbd72TdDoo5SbwavgLj1xjDLbcgkBKVfvbWPleu5+vzDO8ItBjHxZavG/K8N1BJIQgkv6KIdoi/G+dDelDeKZ+6ahOir2uPfnLzDX5JfaTxnPvVe+7l6uQ/lPw08CyYZ5BR0QqcWtwzRfwAtg+mWpddcrOQOiGy92ErdszyGXOfy+GcNgiuyeM37Hzppbhrj6aqNqj0Ieo7KYMELEknyQCk7mABKNX X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 18 Sep 2025 01:52:49 -0700 SeongJae Park wrote: > Hello, > > On Thu, 18 Sep 2025 03:00:29 +0000 Xinyu Zheng wrote: > > > A softlockup issue was found with stress test: [...] > damon_mkold_pmd_entry() calls pte_offset_map_lock(). If the call returns an > error, damon_mkold_pmd_entry() sets walk->action as ACTION_AGAIN, to retry. If > the pte_offset_map_lock() continues fails, infinite loop can happen. I > understand the loop you mentioned above is this case. > > The error handling (retrying) was introduced by commit 7780d04046a2 > ("mm/pagewalkers: ACTION_AGAIN if pte_offset_map_lock() fails"). I added Hugh to this thread from the original mail of this reply, because he is the author of the commit. I should clarified this on the original mail but forgot saying that, sorry. Thanks, SJ [...]