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([2601:188:c100:5710:627d:9ff:fe85:9ade]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6e65d7a3c20sm86544956d6.53.2025.02.20.06.22.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 20 Feb 2025 06:22:23 -0800 (PST) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: Date: Thu, 20 Feb 2025 09:22:22 -0500 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/2] hung_task: Dump the blocking task stacktrace To: "Masami Hiramatsu (Google)" , Waiman Long Cc: Lance Yang , Peter Zijlstra , Ingo Molnar , Will Deacon , Andrew Morton , Boqun Feng , Joel Granados , Anna Schumaker , Kent Overstreet , Yongliang Gao , Steven Rostedt , Tomasz Figa , Sergey Senozhatsky , linux-kernel@vger.kernel.org, Linux Memory Management List References: <173997003868.2137198.9462617208992136056.stgit@mhiramat.tok.corp.google.com> <8ca57548-4b18-401d-bfda-95bc12216adf@redhat.com> <20250220231857.6e377e5f208b60a7ba303cea@kernel.org> In-Reply-To: <20250220231857.6e377e5f208b60a7ba303cea@kernel.org> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: UDmzavpREkEVFsW6gQ76AZHCcNbZw7uyGg4EmD-UOQU_1740061345 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 2776014001C X-Stat-Signature: 91jy3zg85h3r78ce8rszqofihouxt78d X-Rspam-User: X-HE-Tag: 1740061346-220121 X-HE-Meta: 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 IUPMDVUy 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000002, 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 2/20/25 9:18 AM, Masami Hiramatsu (Google) wrote: > On Wed, 19 Feb 2025 15:20:39 -0500 > Waiman Long wrote: > >> On 2/19/25 10:02 AM, Lance Yang wrote: >>> On Wed, Feb 19, 2025 at 9:33 PM Lance Yang wrote: >>>> CC linux-mm >>>> >>>> On Wed, Feb 19, 2025 at 9:00 PM Masami Hiramatsu (Google) >>>> wrote: >>>>> Hi, >>>>> >>>>> The hung_task detector is very useful for detecting the lockup. >>>>> However, since it only dumps the blocked (uninterruptible sleep) >>>>> processes, it is not enough to identify the root cause of that >>>>> lockup. >>>>> >>>>> For example, if a process holds a mutex and sleep an event in >>>>> interruptible state long time, the other processes will wait on >>>>> the mutex in uninterruptible state. In this case, the waiter >>>>> processes are dumped, but the blocker process is not shown >>>>> because it is sleep in interruptible state. >>> Cool! I just ran into something similar today, but with rwsem. In that >>> case, the blocked process was locked up, and we could not identify >>> the root cause either ;( >> Once this patch series is settled down, we can extend rwsem to provide >> similar feature. > While discussing about rwsem with Sergey, he pointed that we can not > identify a single blocker on rwsem, because several readers can block > several writers. In this case, we need to dump all of them but we > don't have such info. > > So anyway, I would like to start from mutex, which is the simplest one. > For the other locks, we will discuss later. (or start with limited > support, like showing only rwsem::owner) Yes, reader tracking is a problem as the rw_semaphore structure doesn't store information about the reader-owners as the count can vary. That is a limitation that we have to live with. Cheers, Longman