gpu: nvgpu: add safe channel id lookup

Add gk20a_channel_from_id() to retrieve a channel, given a raw channel
ID, with a reference taken (or NULL if the channel was dead). This makes
it harder to mistakenly use a channel that's dead and thus uncovers bugs
sooner. Convert code to use the new lookup when applicable; work remains
to convert complex uses where a ref should have been taken but hasn't.

The channel ID is also validated against FIFO_INVAL_CHANNEL_ID; NULL is
returned for such IDs. This is often useful and does not hurt when
unnecessary.

However, this does not prevent the case where a channel would be closed
and reopened again when someone would hold a stale channel number. In
all such conditions the caller should hold a reference already.

The only conditions where a channel can be safely looked up by an id and
used without taking a ref are when initializing or deinitializing the
list of channels.

Jira NVGPU-1460

Change-Id: I0a30968d17c1e0784d315a676bbe69c03a73481c
Signed-off-by: Konsta Holtta <kholtta@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/1955400
Signed-off-by: Debarshi Dutta <ddutta@nvidia.com>
(cherry picked from commit 7df3d587502c2de997dfbe8ea8ddc114d0a0481e
in dev-kernel)
Reviewed-on: https://git-master.nvidia.com/r/2008515
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/gpu/nvgpu/include/nvgpu/channel.h b/drivers/gpu/nvgpu/include/nvgpu/channel.h
index 6cdcb973..1851b9e2 100644
--- a/drivers/gpu/nvgpu/include/nvgpu/channel.h
+++ b/drivers/gpu/nvgpu/include/nvgpu/channel.h
@@ -393,6 +393,11 @@ struct channel_gk20a *__must_check _gk20a_channel_get(struct channel_gk20a *ch,
 void _gk20a_channel_put(struct channel_gk20a *ch, const char *caller);
 #define gk20a_channel_put(ch) _gk20a_channel_put(ch, __func__)
 
+/* returns NULL if could not take a ref to the channel */
+struct channel_gk20a *__must_check _gk20a_channel_from_id(struct gk20a *g,
+                u32 chid, const char *caller);
+#define gk20a_channel_from_id(g, chid) _gk20a_channel_from_id(g, chid, __func__)
+
 int gk20a_wait_channel_idle(struct channel_gk20a *ch);
 
 /* runlist_id -1 is synonym for ENGINE_GR_GK20A runlist id */