linux-kernel - [PATCH v4 1/3] venus: core: handle race condititon for core ops

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Date:   Wed, 16 Sep 2020 14:19:32 +0530
From:   Mansur Alisha Shaik <mansur@...eaurora.org>
To:     linux-media@...r.kernel.org, stanimir.varbanov@...aro.org
Cc:     linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        vgarodia@...eaurora.org,
        Mansur Alisha Shaik <mansur@...eaurora.org>
Subject: [PATCH v4 1/3] venus: core: handle race condititon for core ops

For core ops we are having only write protect but there
is no read protect, because of this in multthreading
and concurrency, one CPU core is reading without wait
which is causing the NULL pointer dereferece crash.

one such scenario is as show below, where in one CPU
core, core->ops becoming NULL and in another CPU core
calling core->ops->session_init().

CPU: core-7:
Call trace:
 hfi_session_init+0x180/0x1dc [venus_core]
 vdec_queue_setup+0x9c/0x364 [venus_dec]
 vb2_core_reqbufs+0x1e4/0x368 [videobuf2_common]
 vb2_reqbufs+0x4c/0x64 [videobuf2_v4l2]
 v4l2_m2m_reqbufs+0x50/0x84 [v4l2_mem2mem]
 v4l2_m2m_ioctl_reqbufs+0x2c/0x38 [v4l2_mem2mem]
 v4l_reqbufs+0x4c/0x5c
__video_do_ioctl+0x2b0/0x39c

CPU: core-0:
Call trace:
 venus_shutdown+0x98/0xfc [venus_core]
 venus_sys_error_handler+0x64/0x148 [venus_core]
 process_one_work+0x210/0x3d0
 worker_thread+0x248/0x3f4
 kthread+0x11c/0x12c

Signed-off-by: Mansur Alisha Shaik <mansur@...eaurora.org>
Acked-by: Stanimir Varbanov <stanimir.varbanov@...aro.org>
---
Changes in V4:
- Addressed review comments by Stan in patch series 
  https://lore.kernel.org/patchwork/patch/1303678/
  and combining this change along with shutdown callback
  as we are facing race conditions with shutdown callback

 drivers/media/platform/qcom/venus/hfi.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/media/platform/qcom/venus/hfi.c b/drivers/media/platform/qcom/venus/hfi.c
index a59022a..58d4c06 100644
--- a/drivers/media/platform/qcom/venus/hfi.c
+++ b/drivers/media/platform/qcom/venus/hfi.c
@@ -195,19 +195,34 @@ EXPORT_SYMBOL_GPL(hfi_session_create);
 int hfi_session_init(struct venus_inst *inst, u32 pixfmt)
 {
 	struct venus_core *core = inst->core;
-	const struct hfi_ops *ops = core->ops;
+	const struct hfi_ops *ops;
 	int ret;
 
+	/*
+	 * If core shutdown is in progress or if we are in system
+	 * recovery, return an error as during system error recovery
+	 * session_init() can't pass successfully
+	 */
+	mutex_lock(&core->lock);
+	if (!core->ops || core->sys_error) {
+		mutex_unlock(&core->lock);
+		return -EIO;
+	}
+	mutex_unlock(&core->lock);
+
 	if (inst->state != INST_UNINIT)
 		return -EINVAL;
 
 	inst->hfi_codec = to_codec_type(pixfmt);
 	reinit_completion(&inst->done);
 
+	mutex_lock(&core->lock);
+	ops = core->ops;
 	ret = ops->session_init(inst, inst->session_type, inst->hfi_codec);
 	if (ret)
 		return ret;
 
+	mutex_unlock(&core->lock);
 	ret = wait_session_msg(inst);
 	if (ret)
 		return ret;
-- 
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