From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f180.google.com ([209.85.192.180]:35208 "EHLO mail-pf0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752346AbcHIATl (ORCPT ); Mon, 8 Aug 2016 20:19:41 -0400 Received: by mail-pf0-f180.google.com with SMTP id x72so123926908pfd.2 for ; Mon, 08 Aug 2016 17:19:41 -0700 (PDT) Date: Mon, 8 Aug 2016 17:19:38 -0700 From: Brian Norris To: Lars-Peter Clausen Cc: Jonathan Cameron , Hartmut Knaack , Peter Meerwald-Stadler , linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, Guenter Roeck , Brian Norris , Peter Zijlstra , Ingo Molnar Subject: [PATCH v2] iio: fix sched WARNING "do not call blocking ops when !TASK_RUNNING" Message-ID: <20160809001937.GA23658@google.com> References: <20160802011244.GA54171@google.com> <37ea974c-9ac6-5a40-0f0e-ee34ef605a08@metafoo.de> <20160802165732.GA3310@localhost> <9a6a7f54-0343-db74-57a2-9f747ae659cc@metafoo.de> <20160804082621.GA11331@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20160804082621.GA11331@localhost> Sender: linux-iio-owner@vger.kernel.org List-Id: linux-iio@vger.kernel.org When using CONFIG_DEBUG_ATOMIC_SLEEP, the scheduler nicely points out that we're calling sleeping primitives within the wait_event loop, which means we might clobber the task state: [ 10.831289] do not call blocking ops when !TASK_RUNNING; state=1 set at [] [ 10.845531] ------------[ cut here ]------------ [ 10.850161] WARNING: at kernel/sched/core.c:7630 ... [ 12.164333] ---[ end trace 45409966a9a76438 ]--- [ 12.168942] Call trace: [ 12.171391] [] __might_sleep+0x64/0x90 [ 12.176699] [] mutex_lock_nested+0x50/0x3fc [ 12.182440] [] iio_kfifo_buf_data_available+0x28/0x4c [ 12.189043] [] iio_buffer_ready+0x60/0xe0 [ 12.194608] [] iio_buffer_read_first_n_outer+0x108/0x1a8 [ 12.201474] [] __vfs_read+0x58/0x114 [ 12.206606] [] vfs_read+0x94/0x118 [ 12.211564] [] SyS_read+0x64/0xb4 [ 12.216436] [] el0_svc_naked+0x24/0x28 To avoid this, we should (a la https://lwn.net/Articles/628628/) use the wait_woken() function, which avoids the nested sleeping while still handling races between waiting / wake-events. Signed-off-by: Brian Norris --- v2: * Only add/remove to/from the wait queue once per call * Restore interruptability via explicit signal_pending() call * Refactor to avoid nested loop Note that I did not remove the first (semi-redundant) test for !indio_dev->info, so as to avoid disturbing the error codes used here. drivers/iio/industrialio-buffer.c | 23 +++++++++++++++++------ 1 file changed, 17 insertions(+), 6 deletions(-) diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c index 90462fcf5436..49bf9c59f117 100644 --- a/drivers/iio/industrialio-buffer.c +++ b/drivers/iio/industrialio-buffer.c @@ -107,6 +107,7 @@ ssize_t iio_buffer_read_first_n_outer(struct file *filp, char __user *buf, { struct iio_dev *indio_dev = filp->private_data; struct iio_buffer *rb = indio_dev->buffer; + DEFINE_WAIT_FUNC(wait, woken_wake_function); size_t datum_size; size_t to_wait; int ret; @@ -131,19 +132,29 @@ ssize_t iio_buffer_read_first_n_outer(struct file *filp, char __user *buf, else to_wait = min_t(size_t, n / datum_size, rb->watermark); + add_wait_queue(&rb->pollq, &wait); do { - ret = wait_event_interruptible(rb->pollq, - iio_buffer_ready(indio_dev, rb, to_wait, n / datum_size)); - if (ret) - return ret; + if (!indio_dev->info) { + ret = -ENODEV; + break; + } - if (!indio_dev->info) - return -ENODEV; + if (!iio_buffer_ready(indio_dev, rb, to_wait, n / datum_size)) { + if (signal_pending(current)) { + ret = -ERESTARTSYS; + break; + } + + wait_woken(&wait, TASK_INTERRUPTIBLE, + MAX_SCHEDULE_TIMEOUT); + continue; + } ret = rb->access->read_first_n(rb, n, buf); if (ret == 0 && (filp->f_flags & O_NONBLOCK)) ret = -EAGAIN; } while (ret == 0); + remove_wait_queue(&rb->pollq, &wait); return ret; } -- 2.8.0.rc3.226.g39d4020