From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-182.mta0.migadu.com (out-182.mta0.migadu.com [91.218.175.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5361D2E8B82 for ; Mon, 2 Feb 2026 15:29:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770046145; cv=none; b=J03CISKicFQ+5kU+uMoTDLNU3yrAZVY9dTgyYDdTVEkg/ofrKmTB6nY2F7HTrRNlAGu31V49/NwDQrXjcPB2/EaBIsDsCQJ41wK5Csb+YVL3xOJ42wNMdVowe+3wRNd4mX4mbdTZUrJnaM7BjBzPtrAjedVY15gmBgQc4Xtws3E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770046145; c=relaxed/simple; bh=n8nPb95OAv50P4UALPzgR41/K79pVRuV+Y1TanlonZ4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ezPtz3BTWFhJrygwMSNYzXOfquFwM9n1cfMFcxEv/0QBeoq6simey4K/2hxzrVI13YpL7ntOx2hyNPzvYYeZf4Qup90daH443UE/kKNhbaFdOpPxaDWg+uVG4c8m14S5LaZH40+8UQBWm9iy+hwCDEfdFEZ9D3uOLX7rPIC4QlE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=ZlaAJ82o; arc=none smtp.client-ip=91.218.175.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="ZlaAJ82o" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1770046140; h=from:from: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=2u02U3vpF4EplMWQSalMCjafWzF6Hwn57pvK5cjnwuE=; b=ZlaAJ82o+50jBNUMkOuWTLbcvuR+8lAd/ZxJoxpR4q9vnWYuynwk+wPrDxB3KPtClbgbZh kkuHIe1pXITvGGQ6YswYiVmr0C2whqDm75HN9RYpfAhP0pV86zkWNqcefTDSewhyvcoqpn 2ou9O8bTGylxCkYJgJJJmpfi16qyqZw= Date: Mon, 2 Feb 2026 23:28:53 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [v2 PATCH 1/1] hung_task: Explicitly report I/O wait state in log output Content-Language: en-US To: Petr Mladek , Aaron Tomlin Cc: akpm@linux-foundation.org, mhiramat@kernel.org, gregkh@linuxfoundation.org, joel.granados@kernel.org, neelx@suse.com, sean@ashe.io, mproche@gmail.com, chjohnst@gmail.com, nick.lange@gmail.com, linux-kernel@vger.kernel.org References: <20260128204516.3473709-1-atomlin@atomlin.com> <20260128204516.3473709-2-atomlin@atomlin.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2026/2/2 23:14, Petr Mladek wrote: > On Wed 2026-01-28 15:45:16, Aaron Tomlin wrote: >> Currently, the hung task reporting mechanism indiscriminately labels all >> TASK_UNINTERRUPTIBLE (D) tasks as "blocked", irrespective of whether they >> are awaiting I/O completion or kernel locking primitives. This ambiguity >> compels system administrators to manually inspect stack traces to discern >> whether the delay stems from an I/O wait (typically indicative of >> hardware or filesystem anomalies) or software contention. Such detailed >> analysis is not always immediately accessible to system administrators >> or support engineers. >> >> To address this, this patch utilises the existing in_iowait field within >> struct task_struct to augment the failure report. If the task is blocked >> due to I/O (e.g., via io_schedule_prepare()), the log message is updated >> to explicitly state "blocked in I/O wait". >> >> Examples: >> - Standard Block: "INFO: task bash:123 blocked for more than 120 >> seconds". >> >> - I/O Block: "INFO: task dd:456 blocked in I/O wait for more than >> 120 seconds". >> >> Accessing in_iowait is safe in this context. The detector holds >> rcu_read_lock() within check_hung_uninterruptible_tasks(), ensuring the >> task structure remains valid in memory. > > This part is true. > >> Furthermore, as the task is >> confirmed to be in a persistent TASK_UNINTERRUPTIBLE state, it cannot >> modify its own in_iowait flag, rendering the read operation stable and >> free from data races. > > Strictly speaking, this is not true. IMHO, nothing prevents the task > from waking up in parallel. Just the chance is small. > > I would say that the information will be valid in 99.99% of situations > because the message is printed only when the task has been stuck > in the state for a long time. A possible mistake should be > visible from the later printed backtrace. > >> --- a/kernel/hung_task.c >> +++ b/kernel/hung_task.c >> @@ -250,8 +250,9 @@ static void hung_task_info(struct task_struct *t, unsigned long timeout, >> if (sysctl_hung_task_warnings || hung_task_call_panic) { >> if (sysctl_hung_task_warnings > 0) >> sysctl_hung_task_warnings--; >> - pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n", >> - t->comm, t->pid, (jiffies - t->last_switch_time) / HZ); >> + pr_err("INFO: task %s:%d blocked %s for more than %ld seconds.\n", > > s/blocked %s for/blocked%s for/ > >> + t->comm, t->pid, t->in_iowait ? "in I/O wait" : "", > > and here: " in I/O wait". > > Otherwise, it would print two spaces in the non-io case, like" > > "INFO: task bash:123 blocked for more than 120 seconds" Good catch! > >> + (jiffies - t->last_switch_time) / HZ); >> pr_err(" %s %s %.*s\n", >> print_tainted(), init_utsname()->release, >> (int)strcspn(init_utsname()->version, " "), > > Otherwise, it looks good. Other than that, looks good to me.