[PATCH v2 1/3] venus: core: handle race condititon for core ops

[Mansur Alisha Shaik]

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@xxxxxxxxxxxxxx>
Acked-by: Stanimir Varbanov <stanimir.varbanov@xxxxxxxxxx>
---
Changes in V2:
- Addressed review comments by stan by validating on top
- of https://lore.kernel.org/patchwork/project/lkml/list/?series=455962

 drivers/media/platform/qcom/venus/hfi.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/media/platform/qcom/venus/hfi.c b/drivers/media/platform/qcom/venus/hfi.c
index a59022a..3137071 100644
--- a/drivers/media/platform/qcom/venus/hfi.c
+++ b/drivers/media/platform/qcom/venus/hfi.c
@@ -195,7 +195,7 @@ 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 (inst->state != INST_UNINIT)
@@ -204,10 +204,13 @@ int hfi_session_init(struct venus_inst *inst, u32 pixfmt)
 	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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