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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1740061142; bh=QDV5g8FGlk1PKGA8+qOmRMSnu6kXIaPu1NrxOeUEEus=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=CPRzJH9lrL89V6GMsTdLhx5uSzTjLkgR4NcbDpLlxeN5/whY5+WadHOWnxq2xU5X9 MJLqxOiGMBwVRiCxyGo8UJxa7u3OedspofMhEI5cpGZG4vecSvTioze9vhtED4yJSJ rugBuKxRhNaTSxtH6NsOAJQPZ6UV1L0fhe/JSG9A3kiRaq8CdiK+7hHoUAAQJTBGc6 B04qJ3OgZlVaOUmtEOit08B65sZAjxI68TrQ0CX6u7H0LJqcp5Kkf7ppOBJCC3JFtf LPeOfC+QdL3A2D5hKjTi6mODWTvO7/WQSVPIHMfQvEp1QdOxwyRqWje4tesSxTcKRR Yu45u3fuZVLFw== Date: Thu, 20 Feb 2025 23:18:57 +0900 From: Masami Hiramatsu (Google) To: Waiman Long Cc: Lance Yang , mhiramat@kernel.org, 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 Subject: Re: [PATCH 0/2] hung_task: Dump the blocking task stacktrace Message-Id: <20250220231857.6e377e5f208b60a7ba303cea@kernel.org> In-Reply-To: <8ca57548-4b18-401d-bfda-95bc12216adf@redhat.com> References: <173997003868.2137198.9462617208992136056.stgit@mhiramat.tok.corp.google.com> <8ca57548-4b18-401d-bfda-95bc12216adf@redhat.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: A601B20011 X-Stat-Signature: irqj7ajteoh5e51ue3g1e5yoaiewcx8q X-Rspam-User: X-HE-Tag: 1740061143-136719 X-HE-Meta: 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 4Bo4asNb iLS54yt2QQwzJQCOxQ9REBgc0e4R1KC2T4wqkaqXkP0l/7DIF/HwxU11NTNQb7mObdQPXbZ1RI19NF8gBu+rNXAhVitJKgVKcRueGew8fDPBesSdgKITEgmKf9h178nhPM/+XmW+riFyhD7vaz2SKvhmmlBHmt0BJcHL48ToltYNLXdGh7cUi6FoniplQuD9o/sCtEHUe3Xg4zoFroZ5rDAv7ICdA1TelGfxJiDcDXY5Gy+0JZJPKhggybDYWqZY1Mj/oZTwShi+3QI/a5SQDZwXx6dH45mmWA4fK/Yp6KOldSgPgvh2tGR2aMFUZ2I6EfbuWRGalDdrF3t3Pk4Q2DCgyBgF+FfaA0Ae9WL/qfxa1Y+246bFO0r//WEQ3+0F4JND3sx0mbXI3QRMpgdGokYDam7rgFh9KYwJXvUxQzqa4yZhHFy/Kv2PWOIbcE0tPUm0n5ITWibO6+sQ= 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 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) Thanks, -- Masami Hiramatsu (Google)