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a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1740018407; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VzIAwpNUmWerXOqDlJFyQELIArgUPvv6tmJZYtm2tO4=; b=UCn5gBiMUVrnmiLc9vBK12WRqOU2kvfn6MdEMGeJ3nr74kkyccfOVLeR4tQQZIZR7wu2j1 YStl7xN30O0Yivh6h6Fz8Lwuuto6KtI5AWKdGPCPmkE2QUOD9Ee8Aa97L6CM1hyRGnuUdP ObMl2HID5UjCcQ57IeIuDRgFxDElCB0= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id C50A85C5D0B; Thu, 20 Feb 2025 02:26:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EDB23C4CED1; Thu, 20 Feb 2025 02:26:43 +0000 (UTC) Date: Wed, 19 Feb 2025 21:27:08 -0500 From: Steven Rostedt To: Waiman Long Cc: "Masami Hiramatsu (Google)" , 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 Subject: Re: [PATCH 1/2] hung_task: Show the blocker task if the task is hung on mutex Message-ID: <20250219212708.78b93a84@gandalf.local.home> In-Reply-To: <9f9150b4-1cf5-4380-b431-419f70775a7d@redhat.com> 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> <20250220075639.298616eb494248d390417977@kernel.org> <20250219204153.65ed1f5e@gandalf.local.home> <9f9150b4-1cf5-4380-b431-419f70775a7d@redhat.com> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 1B6BA40014 X-Stat-Signature: k7idzu3rqdyghbnoo8z68gtb9s66g439 X-Rspam-User: X-HE-Tag: 1740018406-570447 X-HE-Meta: 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 L4Yc8Yry 3+woUj2kGAtz+7EMBKykcN63kYX7mhlMMQoqeoEcT7pExfd130w5Nw40kh/yJ31OCwJrkAk/kCBeH+pRuSPVDTG4n9xDU+82Uaiv3n+tHa1wzqd7tcJL13ojdMM7eZ8qUgGqohoOMMZWJOJm4mnvnaCEpVphwDIThDmskcHcnbOVu33R0ldPDWi8Gv1Qsjh1mp9JeZFmqVPTr0QBDO2rwRPpsPQWDOK/1BPA9VywlWcHT1wjNZvyAT5/Mp3utcWZsnlHf3U7QOWdOMTQBscEkZkT2m4Wz3RsOOVTMv4BMOpFsN8mTHB1zvd8XqYxhDJUGD4DGwWsJSlffkXGyQLz5lK4AGVnZcUu/DJioi2a1S89Z2SvejdPYj8cV/jvyqSUDi8cOQtMzkBmZ3Gk= 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 21:15:08 -0500 Waiman Long wrote: > Writer - setting them: >=20 > =C2=A0=C2=A0=C2=A0 WRITE_ONCE(lock) > =C2=A0=C2=A0=C2=A0 smp_wmb() > =C2=A0=C2=A0=C2=A0 WRITE_ONCE(type) >=20 > Clearing them: >=20 > =C2=A0=C2=A0=C2=A0 WRITE_ONCE(type, 0) > =C2=A0=C2=A0=C2=A0 smp_wmb() > =C2=A0=C2=A0=C2=A0 WRITE_ONCE(lock, NULL) >=20 > Reader: >=20 > =C2=A0=C2=A0=C2=A0 READ_ONCE(type) > again: > =C2=A0=C2=A0=C2=A0 smp_rmb() > =C2=A0=C2=A0=C2=A0 READ_ONCE(lock) > =C2=A0=C2=A0=C2=A0 smp_rmb() > =C2=A0=C2=A0=C2=A0 if (READ_ONCE(type) !=3D type) > =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 goto again Do you really need the READ/WRITE_ONCE() with the memory barriers? From what I understand, the compiler can't even assume what it read is the same after passing a memory barrier like that. So there should be no reason it can reread the memory location after a barrier. -- Steve