From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mailout4.w1.samsung.com ([210.118.77.14]:55692 "EHLO mailout4.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751427AbbHQM0X (ORCPT ); Mon, 17 Aug 2015 08:26:23 -0400 Received: from eucpsbgm1.samsung.com (unknown [203.254.199.244]) by mailout4.w1.samsung.com (Oracle Communications Messaging Server 7.0.5.31.0 64bit (built May 5 2014)) with ESMTP id <0NT8008QX7VXBJ00@mailout4.w1.samsung.com> for linux-media@vger.kernel.org; Mon, 17 Aug 2015 13:26:21 +0100 (BST) Subject: Re: [PATCH v2] [media] m2m: fix bad unlock balance To: Zahari Doychev , linux-media@vger.kernel.org, hverkuil@xs4all.nl, kamil@wypas.org References: <0fb928455b6cd997c70f4fe1c04fb79a01190b5e.1439805593.git.zahari.doychev@linux.com> Cc: mchehab@osg.samsung.com From: Marek Szyprowski Message-id: <55D1D2EC.3010205@samsung.com> Date: Mon, 17 Aug 2015 14:26:20 +0200 MIME-version: 1.0 In-reply-to: <0fb928455b6cd997c70f4fe1c04fb79a01190b5e.1439805593.git.zahari.doychev@linux.com> Content-type: text/plain; charset=utf-8; format=flowed Content-transfer-encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: Hello, On 2015-08-17 12:13, Zahari Doychev wrote: > This patch removes unnecessary mutex queue unlock/lock sequence causing bad > unlock balance in v4l2_m2m_poll when the last buffer on the destination > queue has been dequeued and adds spin lock protection for the done list > list_empty calls. > > [ 144.990873] ===================================== > [ 144.995584] [ BUG: bad unlock balance detected! ] > [ 145.000301] 4.1.0-00137-ga105070 #98 Tainted: G W > [ 145.006140] ------------------------------------- > [ 145.010851] demux:sink/487 is trying to release lock (&dev->dev_mutex) at: > [ 145.017785] [<808cc578>] mutex_unlock+0x18/0x1c > [ 145.022322] but there are no more locks to release! > [ 145.027205] > [ 145.027205] other info that might help us debug this: > [ 145.033741] no locks held by demux:sink/487. > [ 145.038015] > [ 145.038015] stack backtrace: > [ 145.042385] CPU: 2 PID: 487 Comm: demux:sink Tainted: G W 4.1.0-00137-ga105070 #98 > [ 145.051089] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree) > [ 145.057622] Backtrace: > [ 145.060102] [<80014a4c>] (dump_backtrace) from [<80014cc4>] (show_stack+0x20/0x24) > [ 145.067679] r6:80cedf78 r5:00000000 r4:00000000 r3:00000000 > [ 145.073421] [<80014ca4>] (show_stack) from [<808c61e0>] (dump_stack+0x8c/0xa4) > [ 145.080661] [<808c6154>] (dump_stack) from [<80072b64>] (print_unlock_imbalance_bug+0xb8/0xe8) > [ 145.089277] r6:808cc578 r5:ac6cd050 r4:ac38e400 r3:00000001 > [ 145.095020] [<80072aac>] (print_unlock_imbalance_bug) from [<80077db4>] (lock_release+0x1a4/0x250) > [ 145.103983] r6:808cc578 r5:ac6cd050 r4:ac38e400 r3:00000000 > [ 145.109728] [<80077c10>] (lock_release) from [<808cc470>] (__mutex_unlock_slowpath+0xc4/0x1b4) > [ 145.118344] r9:acb27a41 r8:00000000 r7:81553814 r6:808cc578 r5:60030013 r4:ac6cd01c > [ 145.126190] [<808cc3ac>] (__mutex_unlock_slowpath) from [<808cc578>] (mutex_unlock+0x18/0x1c) > [ 145.134720] r7:00000000 r6:aced7cd4 r5:00000041 r4:acb87800 > [ 145.140468] [<808cc560>] (mutex_unlock) from [<805a98b8>] (v4l2_m2m_fop_poll+0x5c/0x64) > [ 145.148494] [<805a985c>] (v4l2_m2m_fop_poll) from [<805955a0>] (v4l2_poll+0x6c/0xa0) > [ 145.156243] r6:aced7bec r5:00000000 r4:ac6cc380 r3:805a985c > [ 145.161991] [<80595534>] (v4l2_poll) from [<80156edc>] (do_sys_poll+0x230/0x4c0) > [ 145.169391] r5:00000000 r4:aced7be4 > [ 145.173013] [<80156cac>] (do_sys_poll) from [<801574a8>] (SyS_ppoll+0x1d4/0x1fc) > [ 145.180414] r10:00000000 r9:aced6000 r8:00000000 r7:00000000 r6:75c04538 r5:00000002 > [ 145.188338] r4:00000000 > [ 145.190906] [<801572d4>] (SyS_ppoll) from [<800108c0>] (ret_fast_syscall+0x0/0x54) > [ 145.198481] r8:80010aa4 r7:00000150 r6:75c04538 r5:00000002 r4:00000008 > > Signed-off-by: Zahari Doychev Acked-by: Marek Szyprowski > --- > drivers/media/v4l2-core/v4l2-mem2mem.c | 23 ++++++++--------------- > 1 file changed, 8 insertions(+), 15 deletions(-) > > diff --git a/drivers/media/v4l2-core/v4l2-mem2mem.c b/drivers/media/v4l2-core/v4l2-mem2mem.c > index ec3ad4e..2f7291c 100644 > --- a/drivers/media/v4l2-core/v4l2-mem2mem.c > +++ b/drivers/media/v4l2-core/v4l2-mem2mem.c > @@ -583,32 +583,25 @@ unsigned int v4l2_m2m_poll(struct file *file, struct v4l2_m2m_ctx *m2m_ctx, > goto end; > } > > - if (m2m_ctx->m2m_dev->m2m_ops->unlock) > - m2m_ctx->m2m_dev->m2m_ops->unlock(m2m_ctx->priv); > - else if (m2m_ctx->q_lock) > - mutex_unlock(m2m_ctx->q_lock); > - > + spin_lock_irqsave(&src_q->done_lock, flags); > if (list_empty(&src_q->done_list)) > poll_wait(file, &src_q->done_wq, wait); > + spin_unlock_irqrestore(&src_q->done_lock, flags); > + > + spin_lock_irqsave(&dst_q->done_lock, flags); > if (list_empty(&dst_q->done_list)) { > /* > * If the last buffer was dequeued from the capture queue, > * return immediately. DQBUF will return -EPIPE. > */ > - if (dst_q->last_buffer_dequeued) > + if (dst_q->last_buffer_dequeued) { > + spin_unlock_irqrestore(&dst_q->done_lock, flags); > return rc | POLLIN | POLLRDNORM; > + } > > poll_wait(file, &dst_q->done_wq, wait); > } > - > - if (m2m_ctx->m2m_dev->m2m_ops->lock) > - m2m_ctx->m2m_dev->m2m_ops->lock(m2m_ctx->priv); > - else if (m2m_ctx->q_lock) { > - if (mutex_lock_interruptible(m2m_ctx->q_lock)) { > - rc |= POLLERR; > - goto end; > - } > - } > + spin_unlock_irqrestore(&dst_q->done_lock, flags); > > spin_lock_irqsave(&src_q->done_lock, flags); > if (!list_empty(&src_q->done_list)) Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland