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, 4 insertions, 5 deletions

diff --git a/drivers/gpu/nvgpu/gp10b/gr_gp10b.c b/drivers/gpu/nvgpu/gp10b/gr_gp10b.c
index f70a5a00..a3655146 100644
--- a/drivers/gpu/nvgpu/gp10b/gr_gp10b.c
+++ b/drivers/gpu/nvgpu/gp10b/gr_gp10b.c
@@ -1961,8 +1961,8 @@ static int gr_gp10b_get_cilp_preempt_pending_chid(struct gk20a *g, int *__chid)
 
         chid = g->gr.cilp_preempt_pending_chid;
 
-        ch = gk20a_channel_get(gk20a_fifo_channel_from_chid(g, chid));
-        if (!ch) {
+        ch = gk20a_channel_from_id(g, chid);
+        if (ch == NULL) {
                 return ret;
         }
 
@@ -2014,9 +2014,8 @@ int gr_gp10b_handle_fecs_error(struct gk20a *g,
                         goto clean_up;
                 }
 
-                ch = gk20a_channel_get(
-                                gk20a_fifo_channel_from_chid(g, chid));
-                if (!ch) {
+                ch = gk20a_channel_from_id(g, chid);
+                if (ch == NULL) {
                         goto clean_up;
                 }