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([2601:188:c100:5710:627d:9ff:fe85:9ade]) by smtp.gmail.com with ESMTPSA id 5614622812f47-3f3ffedc858sm1921820b6e.4.2025.02.19.17.40.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 19 Feb 2025 17:40:04 -0800 (PST) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: <141d77e3-19e0-4f1b-9049-13dca0d5f339@redhat.com> Date: Wed, 19 Feb 2025 20:40:02 -0500 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] hung_task: Show the blocker task if the task is hung on mutex To: "Masami Hiramatsu (Google)" , Steven Rostedt Cc: Waiman Long , Peter Zijlstra , Ingo Molnar , Will Deacon , Andrew Morton , Boqun Feng , Joel Granados , Anna Schumaker , Lance Yang , Kent Overstreet , Yongliang Gao , Tomasz Figa , Sergey Senozhatsky , linux-kernel@vger.kernel.org, Linux Memory Management List References: <173997003868.2137198.9462617208992136056.stgit@mhiramat.tok.corp.google.com> <173997004932.2137198.7959507113210521328.stgit@mhiramat.tok.corp.google.com> <20250219112308.5d905680@gandalf.local.home> <0fa9dd8e-2d83-487e-bfb1-1f5d20cd9fe6@redhat.com> <20250219152435.35077ac3@gandalf.local.home> <20250220080908.fc1494f0f7c611b48fbe0f8b@kernel.org> In-Reply-To: <20250220080908.fc1494f0f7c611b48fbe0f8b@kernel.org> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: k2SoWPnGh-HVfFhJ-j1TPv3jYvub5oGT3cb1OxVfEPQ_1740015605 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 8F56520004 X-Rspamd-Server: rspam12 X-Stat-Signature: 876it4r7ktc5h4o7b7uxeythswe6yzs6 X-HE-Tag: 1740015611-199585 X-HE-Meta: U2FsdGVkX1+d0xOEPp+8RK47T7rinzM0+GMqO4+sFJXO0xNFCB1/2Co4IIJ2A+XpMXZSjgyBktxu8Em7+GmGVwyQOF5EFn2AOs6jUTT2yD1jmDmPBOw7aEnsS2NM6Ll2cRgfWR5211nLyNwtXe6Ol60GD0KJvSKJV3jPFMoWxiMA5FCPyct6YwkyYf6hfoE0V6MN6pHdgib7tyfZDfSSS/9j1qk7U+Q58h1TBqh0vbLt5PwUsuGqF351Ta47B1OLFFdms/Ijfsgn7Qmkd4Wyn9zPeeJh9roVjXF4cLDuzlB72GHgQkL0rs8G4Ea6fAXHkd/nL+ztUcQ1cl4SwuPOdru5/w+1CWhrDeABoCUhVH5mkPjcDvUhzM6sPQ52Ti2dG6Mti9CMQEp59wMq75kiYNQtGV1tMz7pX3akizt5CmQ6BrJB5zuc8ddohfBLsDKLnLCyG6zsxq18mKJwAGImzABPbHqBVNPA00RDALfMJRTXX/Q2Vt85xECSpTnx4onFEqY2/K37oHXboUqBZFEz9wL+EWPm+IRb7Kv/pUS/KnJLMkmVSwtGvB3rTUgBQO3nF5MZuPJPbhu4NNnrCoUQyy74YKCURpcj3ltwXfNist1Q32875PEB6wW7Xu9+UfwBUYSwmmRvqzjsEi55pCdMUtoSJmTNspqG3YY1Gkqv8mn4bsL45ao1s6M850qL+NTUzjJLiKK65Pb3BJMj66smv1pOv2xON5/GSdXKgimlxkXcagMqXbeI7Qug5XZhQneyJg0t3TNFjIitmLJ9ozcF04r16lTfycsx8fKm/FOBGyT853m27jU52GdfFrPjll+xZzDx7Whrqoz6st8KT8q3Dpl5STpsRHDT9kTIP8A1Iktw4VvdjXpykg4SmhTMiVP9bUY6nkck0zNhdWPFNIrDe9r1JRRMZO5AF1MCVQvkybU6elnpURXSNNYkY/zoE88Im1gNK6AO5AQMWvyCLV8 VGlv0OKv 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000022, 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 2/19/25 6:09 PM, Masami Hiramatsu (Google) wrote: > On Wed, 19 Feb 2025 15:24:35 -0500 > Steven Rostedt wrote: > >> On Wed, 19 Feb 2025 15:18:57 -0500 >> Waiman Long wrote: >> >>> It is tricky to access the mutex_waiter structure which is allocated >>> from stack. So another way to work around this issue is to add a new >>> blocked_on_mutex field in task_struct to directly point to relevant >>> mutex. Yes, that increase the size of task_struct by 8 bytes, but it is >>> a pretty large structure anyway. Using READ_ONCE/WRITE_ONCE() to access >> And it's been on my TODO list for some time to try to make that structure >> smaller again :-/ >> >>> this field, we don't need to take lock, though taking the wait_lock may >>> still be needed to examine other information inside the mutex. >> But perhaps if we add a new config option for this feature, we could just >> add the lock that a task is blocked on before it goes to sleep and >> reference that instead. That would be easier than trying to play games >> getting the lock owner from the blocked_on field. > So something like this? > > unsigned int block_flags; > union { > struct mutex *mutex; > struct rwsem +rwsem; > struct rtmutex *rtmutex; > } blocked_on; > > enum { > BLOCKED_ON_MUTEX; > BLOCKED_ON_RWSEM; > BLOCKED_ON_RTMUTEX; > BLOCKED_ON_IO; > } block_reason; You should add one enum, e.g. BLOCKED_NONE, to represent the normal state of not being blocked. Cheers, Longman > For the safety, we may anyway lock the task anyway, but that is the > same as stacktrace. > > Thank you, > >> -- Steve >