Patch "selftests/powerpc: Fix TM resched DSCR test with some compilers" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

selftests/powerpc: Fix TM resched DSCR test with some compilers

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
selftests-powerpc-fix-tm-resched-dscr-test-with-some-compilers.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Michael Ellerman <[email protected]>
Date: Fri, 19 May 2017 11:29:04 +1000
Subject: selftests/powerpc: Fix TM resched DSCR test with some compilers

From: Michael Ellerman <[email protected]>

[ Upstream commit fe06fe860250a4f01d0eaf70a2563b1997174a74 ]

The tm-resched-dscr test has started failing sometimes, depending on what compiler it's built with, eg:

test: tm_resched_dscr
Check DSCR TM context switch: tm-resched-dscr: tm-resched-dscr.c:76: test_body: Assertion `rv' failed. !! child died by signal 6

When it fails we see that the compiler doesn't initialise rv to 1 before entering the inline asm block. Although that's counter intuitive, it is allowed because we tell the compiler that the inline asm will write to rv (using "=r"), meaning the original value is irrelevant.

Marking it as a read/write parameter would presumably work, but it seems simpler to fix it by setting the initial value of rv in the inline asm.

---
 tools/testing/selftests/powerpc/tm/tm-resched-dscr.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -45,12 +45,12 @@ int test_body(void)
 	printf("Check DSCR TM context switch: ");
 	fflush(stdout);
 	for (;;) {
-		rv = 1;
 		asm __volatile__ (
 			/* set a known value into the DSCR */
 			"ld      3, %[dscr1];"
 			"mtspr   %[sprn_dscr], 3;"
 
+			"li      %[rv], 1;"
 			/* start and suspend a transaction */
 			TBEGIN
 			"beq     1f;"

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/selftests-powerpc-fix-tm-resched-dscr-test-with-some-compilers.patch queue-4.4/powerpc-mm-fix-virt_addr_valid-etc.-on-64-bit-hash.patch queue-4.4/powerpc-spufs-fix-coredump-of-spu-contexts.patch queue-4.4/signal-powerpc-document-conflicts-with-si_user-and-sigfpe-and-sigtrap.patch queue-4.4/powerpc-don-t-clobber-tcr-when-setting-tcr.patch