From nobody Mon Feb 9 07:32:48 2026 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 90A3E5CDF5; Fri, 8 Mar 2024 20:22:34 +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=1709929354; cv=none; b=NDuuAmLKlErnXU/xY/COiSL1knGYPcRNrLiYlSiOFfKfLbitAMtVig+2+ciCbze807Rr80opkOg33EXK0U68vLiPJJzJbMhQCfpN6KvDs7ovIooSK14jtkTxd9Pgs0DZJUWvFj0INpxNSuForX/J1RrnAIu58hL6WThIEhO7r0I= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709929354; c=relaxed/simple; bh=YI8/vnqPugKBuZi57m6Pdrz5Fc9pTxcOvLj/2eGyPhk=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=ktwqHdYxfQwHXiULvnyZ5RdjBI12QDw9qcyKxaPa3x8rCXtLxuybpXliGJ4SmFZiUxlika65XScifnUJIvqCONTawTibBkA8+ZKlVaCiU/x4bdhWkOsXkgbvsW8Jyyp55dxj9IupT+7BR6LOrB00Zf3cLsu3IEP4/U+B07ILTzc= 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 4486BC433B1; Fri, 8 Mar 2024 20:22:34 +0000 (UTC) Received: from rostedt by gandalf with local (Exim 4.97) (envelope-from ) id 1riglc-00000000yrd-12ic; Fri, 08 Mar 2024 15:24:32 -0500 Message-ID: <20240308202432.107909457@goodmis.org> User-Agent: quilt/0.67 Date: Fri, 08 Mar 2024 15:24:05 -0500 From: Steven Rostedt To: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Linus Torvalds , joel@joelfernandes.org, linke li , Rabin Vincent , stable@vger.kernel.org Subject: [PATCH v2 3/6] tracing: Use .flush() call to wake up readers References: <20240308202402.234176464@goodmis.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: "Steven Rostedt (Google)" The .release() function does not get called until all readers of a file descriptor are finished. If a thread is blocked on reading a file descriptor in ring_buffer_wait(), and another thread closes the file descriptor, it will not wake up the other thread as ring_buffer_wake_waiters() is called by .release(), and that will not get called until the .read() is finished. The issue originally showed up in trace-cmd, but the readers are actually other processes with their own file descriptors. So calling close() would w= ake up the other tasks because they are blocked on another descriptor then the one that was closed(). But there's other wake ups that solve that issue. When a thread is blocked on a read, it can still hang even when another thread closed its descriptor. This is what the .flush() callback is for. Have the .flush() wake up the readers. Cc: stable@vger.kernel.org Fixes: f3ddb74ad0790 ("tracing: Wake up ring buffer waiters on closing of t= he file") Signed-off-by: Steven Rostedt (Google) --- kernel/trace/trace.c | 21 +++++++++++++++------ 1 file changed, 15 insertions(+), 6 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index d16b95ca58a7..c9c898307348 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -8393,6 +8393,20 @@ tracing_buffers_read(struct file *filp, char __user = *ubuf, return size; } =20 +static int tracing_buffers_flush(struct file *file, fl_owner_t id) +{ + struct ftrace_buffer_info *info =3D file->private_data; + struct trace_iterator *iter =3D &info->iter; + + iter->wait_index++; + /* Make sure the waiters see the new wait_index */ + smp_wmb(); + + ring_buffer_wake_waiters(iter->array_buffer->buffer, iter->cpu_file); + + return 0; +} + static int tracing_buffers_release(struct inode *inode, struct file *file) { struct ftrace_buffer_info *info =3D file->private_data; @@ -8404,12 +8418,6 @@ static int tracing_buffers_release(struct inode *ino= de, struct file *file) =20 __trace_array_put(iter->tr); =20 - iter->wait_index++; - /* Make sure the waiters see the new wait_index */ - smp_wmb(); - - ring_buffer_wake_waiters(iter->array_buffer->buffer, iter->cpu_file); - if (info->spare) ring_buffer_free_read_page(iter->array_buffer->buffer, info->spare_cpu, info->spare); @@ -8625,6 +8633,7 @@ static const struct file_operations tracing_buffers_f= ops =3D { .read =3D tracing_buffers_read, .poll =3D tracing_buffers_poll, .release =3D tracing_buffers_release, + .flush =3D tracing_buffers_flush, .splice_read =3D tracing_buffers_splice_read, .unlocked_ioctl =3D tracing_buffers_ioctl, .llseek =3D no_llseek, --=20 2.43.0