[PATCH v3] drm/i915/gt: Protect against overflow in active_engine()

[Krzysztof Karas]

It is unlikely, but possible for the first call to
intel_context_create() to fail with -ENOMEM, which would result
in entering the following code block and decrementing "count",
when it is set to 0 (initial condition in the for loop).

Protect from overflowing the variable by checking for 0 value
of "count" before entering the loop.

Signed-off-by: Krzysztof Karas <krzysztof.karas at intel.com>
---

v2:
 * remove unlikely() - Jani
 * replace "while" with "do while" - Andi

v3:
 * use additional check for 0 value instead of changes to the
   "while" loop - Andi

 drivers/gpu/drm/i915/gt/selftest_hangcheck.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/i915/gt/selftest_hangcheck.c b/drivers/gpu/drm/i915/gt/selftest_hangcheck.c
index f057c16410e7..619c70c54ef9 100644
--- a/drivers/gpu/drm/i915/gt/selftest_hangcheck.c
+++ b/drivers/gpu/drm/i915/gt/selftest_hangcheck.c
@@ -904,6 +904,8 @@ static void active_engine(struct kthread_work *work)
 			arg->result = PTR_ERR(ce[count]);
 			pr_err("[%s] Create context #%ld failed: %d!\n",
 			       engine->name, count, arg->result);
+			if (!count)
+				return;
 			while (--count)
 				intel_context_put(ce[count]);
 			return;
-- 
2.34.1

-- 
Best Regards,
Krzysztof