dmaengine: dmatest: warn user when dma test times out

Commit adfa543e7314 ("dmatest: don't use set_freezable_with_signal()") introduced a bug (that is in fact documented by the patch commit text) that leaves behind a dangling pointer. Since the done_wait structure is allocated on the stack, future invocations to the DMATEST can produce undesirable results (e.g., corrupted spinlocks). Ideally, this would be cleaned up in the thread handler, but at the very least, the kernel is left in a very precarious scenario that can lead to some long debug sessions when the crash comes later.

This bug has also been captured at
https://bugzilla.kernel.org/show_bug.cgi?id=197605

---
changes from v1: No longer using BUG at request of Vinod

 drivers/dma/dmatest.c | 1 +
 1 file changed, 1 insertion(+)

index 34ff532..47edc7f 100644
@@ -702,6 +702,7 @@ static int dmatest_func(void *data)
 			 * free it this time?" dancing.  For now, just
 			 * leave it dangling.
 			 */
+			WARN(1, "dmatest: Kernel stack may be corrupted!!\n");
 			dmaengine_unmap_put(um);
 			result("test timed out", total_tests, src_off, dst_off,
 			       len, 0);

Qualcomm Datacenter Technologies as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.

Vinod

Did you have any other feedback on the patch or the wording of the warning?

Thanks

Adam Wallis
Qualcomm Datacenter Technologies as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.

I have made it

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=197605

and applied. Thanks

~Vinod