From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f181.google.com (mail-pg1-f181.google.com [209.85.215.181]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DEE2CB663 for ; Sat, 23 Aug 2025 05:02:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755925376; cv=none; b=rrSwtBPDIRMnAe4FZvwz7baemXAxOAbvv02qxQMHLoO3TWZUqXNoFFsX8Tr2N61Tt8/PiqAc6NsgK9+pN8TUHJ/ijMFnHR7y1rbqyCfan3ExwxflZSdU4j4tWSKeWP4nM6B+0HYDpwO6juPZT/E28e6q7eJ8R8BAOs/M6dnPW5s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755925376; c=relaxed/simple; bh=PUw1CEY9BF2A4FCoMSDLPSzSajO6DMKtVoLXf9xDEPk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=S9NC6dlC5Vmdlz7re5AZD/ICtA0KyztURanG272Um7fPq4IWrQ/Oe+UIkZjQqCaqb9xX9NkMEfYmrgVRnln052UwlezrKBr8/eqHX7G+BV4c8e5EvyDn0dg+JPDneLuL7O9fBvMpKgG4xUTMX7onZF1Xht7hB6YKY9Uft7pwAs8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=gmail.com; arc=none smtp.client-ip=209.85.215.181 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Received: by mail-pg1-f181.google.com with SMTP id 41be03b00d2f7-b49d3b48d8aso8231a12.2 for ; Fri, 22 Aug 2025 22:02:54 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1755925374; x=1756530174; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=/d62ZhyQDkr88P3RsdKpz2BL7mo3EK8sLLtOc02S/I0=; b=KwV5nM0JrxYg4wP/2lilj3WJTLme3PW7ecVsHOxXrO4/ewAG8ME/FecrteTn4YzF7M eKtym1mCbK2Ya67OnZjsP/kleS9UOQqzCSo5t92r89VXIGzLn7W4QxzKwQeVTdUH8IQx F353oIkuwt/wcEp1IRRPtXh8zosZcq4vW8qtthQg0/YTix1JWPQmOYh71i7L8D50dJtD Rt6VGBbwvzjNbqKFxo65M6kbLyIvj4CDJTcwp+gghYnWqPcP7KiZssw63KXjsCcukM2h 7u+gNnPX+b7BGicTuOOtkZEPA0zRq6kclWbn+FhH8tBTOrg12Nzano3F2+sfHlQlmPwt 74HA== X-Forwarded-Encrypted: i=1; AJvYcCWjXHo/n6dGiqxp6DGuueyPN/lIXAWyFNFp+Ct+glbDXR99B4X9tmOzKi2TjyNiMtrAVz2Xk9YRkWYH@lists.linux-m68k.org X-Gm-Message-State: AOJu0YzdXdfKyPa6qltv9xpA4iN10iP09aN0eXgBUkHvBhr3/Khl5VFs W+KhH/3VOdlcFN7T6h7C68gDp005hG1jVzd3rBVApzSfgC/VxBB57uRd X-Gm-Gg: ASbGncvm4SL5REfStR+maVOLHOQiTyaOC9Qcw/BqW4E8bU8KJtsa6uy54UrJBPdga1M AWjILS7k7KcKM025Os6EMIeRzUF8aZDpjNhsAFIV+73AQ47cDwB75e9Wt12jYcNRc+Kq0ICv+HV 11CAszN8QTVkPgoq5/n19p6vJay4EhsTBvsuX+XW++p+rLkJdjr5MQvHiLqNrV98MPoPEwJt9z7 awMuvGHiOxP3dardzTyH0wLudclprQTl2/VmJpEzT9v/4an8l1qnjpA8WmhObyfi/1FM0QzSBTg YZM9NGrdowqY4DzRoJo4adAlyOYcuXT0VBAjn4TjJl5DFwhWLbhRz2UjkgwASyaM97hFeJwtRd/ VLgVx0Ptv7oN0QMRdxrpraDi7rMf5 X-Google-Smtp-Source: AGHT+IE8770SMYUXmPTg9FqFtmb8WBT+htAHMIkfnPossk9y2D5JS3AQrYJBFyN+jCsWvbzmTaOlqA== X-Received: by 2002:a17:902:c946:b0:246:39d7:8e6a with SMTP id d9443c01a7336-24639d78f54mr74824125ad.43.1755925373870; Fri, 22 Aug 2025 22:02:53 -0700 (PDT) Received: from localhost.localdomain ([2403:2c80:17::10:4030]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2466877c732sm11997115ad.1.2025.08.22.22.02.43 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Fri, 22 Aug 2025 22:02:53 -0700 (PDT) From: Lance Yang To: akpm@linux-foundation.org, fthain@linux-m68k.org, geert@linux-m68k.org, mhiramat@kernel.org, senozhatsky@chromium.org Cc: lance.yang@linux.dev, amaindex@outlook.com, anna.schumaker@oracle.com, boqun.feng@gmail.com, ioworker0@gmail.com, joel.granados@kernel.org, jstultz@google.com, kent.overstreet@linux.dev, leonylgao@tencent.com, linux-kernel@vger.kernel.org, linux-m68k@lists.linux-m68k.org, longman@redhat.com, mingo@redhat.com, mingzhe.yang@ly.com, oak@helsinkinet.fi, peterz@infradead.org, rostedt@goodmis.org, tfiga@chromium.org, will@kernel.org, stable@vger.kernel.org Subject: [PATCH 1/1] hung_task: fix warnings caused by unaligned lock pointers Date: Sat, 23 Aug 2025 13:00:36 +0800 Message-ID: <20250823050036.7748-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-m68k@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Lance Yang The blocker tracking mechanism assumes that lock pointers are at least 4-byte aligned to use their lower bits for type encoding. However, as reported by Geert Uytterhoeven, some architectures like m68k only guarantee 2-byte alignment of 32-bit values. This breaks the assumption and causes two related WARN_ON_ONCE checks to trigger. To fix this, the runtime checks are adjusted. The first WARN_ON_ONCE in hung_task_set_blocker() is changed to a simple 'if' that returns silently for unaligned pointers. The second, now-invalid WARN_ON_ONCE in hung_task_clear_blocker() is then removed. Thanks to Geert for bisecting! Reported-by: Geert Uytterhoeven Closes: https://lore.kernel.org/lkml/CAMuHMdW7Ab13DdGs2acMQcix5ObJK0O2dG_Fxzr8_g58Rc1_0g@mail.gmail.com Fixes: e711faaafbe5 ("hung_task: replace blocker_mutex with encoded blocker") Cc: Signed-off-by: Lance Yang --- include/linux/hung_task.h | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/include/linux/hung_task.h b/include/linux/hung_task.h index 34e615c76ca5..69640f266a69 100644 --- a/include/linux/hung_task.h +++ b/include/linux/hung_task.h @@ -20,6 +20,10 @@ * always zero. So we can use these bits to encode the specific blocking * type. * + * Note that on architectures like m68k with only 2-byte alignment, the + * blocker tracking mechanism gracefully does nothing for any lock that is + * not 4-byte aligned. + * * Type encoding: * 00 - Blocked on mutex (BLOCKER_TYPE_MUTEX) * 01 - Blocked on semaphore (BLOCKER_TYPE_SEM) @@ -45,7 +49,7 @@ static inline void hung_task_set_blocker(void *lock, unsigned long type) * If the lock pointer matches the BLOCKER_TYPE_MASK, return * without writing anything. */ - if (WARN_ON_ONCE(lock_ptr & BLOCKER_TYPE_MASK)) + if (lock_ptr & BLOCKER_TYPE_MASK) return; WRITE_ONCE(current->blocker, lock_ptr | type); @@ -53,8 +57,6 @@ static inline void hung_task_set_blocker(void *lock, unsigned long type) static inline void hung_task_clear_blocker(void) { - WARN_ON_ONCE(!READ_ONCE(current->blocker)); - WRITE_ONCE(current->blocker, 0UL); } -- 2.49.0