From patchwork Thu Sep 5 15:33:59 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Steven Rostedt X-Patchwork-Id: 13792624 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 2F241D529; Thu, 5 Sep 2024 15:32:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725550378; cv=none; b=CYhevXBgb1Zr/Js1jGnuQWWwsGSnNzLaWQ3KOM1tSm0p9I98tuwj+w/1kET7Wnw4wM3djrn41fwSTJ55G1K6V25GM+ZINYTcJ3gypLR/vKQ+f8Pq5LB34abJWBhmjpM6SWDw1og+7VNysc2zWNOMG2NGNM5v7S2u9S4AritwVr0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725550378; c=relaxed/simple; bh=xD7MNg+tgLlZMUiUnfeZq+0qhrLx2Q27iIlkruJ7OtM=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type; b=Grdb3Rcwv6kQPINopgTbACqwkdmvKNPBPO4mthufl3NeQkGN4oN7SqSLvcT7mra3NZqpLCCOhOzupIZc8WUdICT221rr2Exa8yJ0jEy/8i1bbE8U2hFZrsUwcc41veSAmWqCfehY8CRxQHeCguUDIY6IJpn8K6ZFHQH69OkOEe0= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2CA42C4CEC5; Thu, 5 Sep 2024 15:32:57 +0000 (UTC) Date: Thu, 5 Sep 2024 11:33:59 -0400 From: Steven Rostedt To: LKML , Linux Trace Kernel Cc: Masami Hiramatsu , Mathieu Desnoyers , Tomas Glozar , John Kacur , "Luis Claudio R. Goncalves" Subject: [PATCH] tracing/timerlat: Add interface_lock around clearing of kthread in stop_kthread() Message-ID: <20240905113359.2b934242@gandalf.local.home> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Steven Rostedt The timerlat interface will get and put the task that is part of the "kthread" field of the osn_var to keep it around until all references are released. But here's a race in the "stop_kthread()" code that will call put_task_struct() on the kthread if it is not a kernel thread. This can race with the releasing of the references to that task struct and the put_task_struct() can be called twice when it should have been called just once. Take the interface_lock() in stop_kthread() to synchronize this change. But to do so, the function stop_per_cpu_kthreads() needs to change the loop from for_each_online_cpu() to for_each_possible_cpu() and remove the cpu_read_lock(), as the interface_lock can not be taken while the cpu locks are held. The only side effect of this change is that it may do some extra work, as the per_cpu variables of the offline CPUs would not be set anyway, and would simply be skipped in the loop. Remove unneeded "return;" in stop_kthread(). Cc: stable@vger.kernel.org Fixes: e88ed227f639e ("tracing/timerlat: Add user-space interface") Signed-off-by: Steven Rostedt (Google) --- kernel/trace/trace_osnoise.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c index 48e5014dd4ab..bbe47781617e 100644 --- a/kernel/trace/trace_osnoise.c +++ b/kernel/trace/trace_osnoise.c @@ -1953,8 +1953,12 @@ static void stop_kthread(unsigned int cpu) { struct task_struct *kthread; + mutex_lock(&interface_lock); kthread = per_cpu(per_cpu_osnoise_var, cpu).kthread; if (kthread) { + per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL; + mutex_unlock(&interface_lock); + if (cpumask_test_and_clear_cpu(cpu, &kthread_cpumask) && !WARN_ON(!test_bit(OSN_WORKLOAD, &osnoise_options))) { kthread_stop(kthread); @@ -1967,8 +1971,8 @@ static void stop_kthread(unsigned int cpu) kill_pid(kthread->thread_pid, SIGKILL, 1); put_task_struct(kthread); } - per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL; } else { + mutex_unlock(&interface_lock); /* if no workload, just return */ if (!test_bit(OSN_WORKLOAD, &osnoise_options)) { /* @@ -1976,7 +1980,6 @@ static void stop_kthread(unsigned int cpu) */ per_cpu(per_cpu_osnoise_var, cpu).sampling = false; barrier(); - return; } } } @@ -1991,12 +1994,8 @@ static void stop_per_cpu_kthreads(void) { int cpu; - cpus_read_lock(); - - for_each_online_cpu(cpu) + for_each_possible_cpu(cpu) stop_kthread(cpu); - - cpus_read_unlock(); } /*