powerpc: Fix DSCR inheritance over fork()

PATCH Applied Anton Blanchard 2 participants 2 messages Dec 9, 2015 – Dec 14, 2015

Subsystems (2)

PowerPC Kselftest

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Anton Blanchard

author

2015-12-09 09:12 UTC #0 lore raw

PATCH 1/1 powerpc: Fix DSCR inheritance over fork()

Two DSCR tests have a hack in them:

/*
* XXX: Force a context switch out so that DSCR
* current value is copied into the thread struct
* which is required for the child to inherit the
* changed value.
*/
sleep(1);

We should not be working around this in the testcase, it is a kernel bug. Fix it by copying the current DSCR to the child, instead of what we had in the thread struct at last context switch.

Signed-off-by Anton Blanchard <[email protected]>

---
 arch/powerpc/kernel/process.c                                 | 2 +-
 tools/testing/selftests/powerpc/dscr/dscr_inherit_exec_test.c | 8 --------
 tools/testing/selftests/powerpc/dscr/dscr_inherit_test.c      | 8 --------
 3 files changed, 1 insertion(+), 17 deletions(-)

arch/powerpc/kernel/process.c +1 -1

index ec10250..fffc2d2 100644
@@ -1282,7 +1282,7 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
 #ifdef CONFIG_PPC64 
 	if (cpu_has_feature(CPU_FTR_DSCR)) {
 		p->thread.dscr_inherit = current->thread.dscr_inherit;
-		p->thread.dscr = current->thread.dscr;
+		p->thread.dscr = mfspr(SPRN_DSCR);
 	}
 	if (cpu_has_feature(CPU_FTR_HAS_PPR))
 		p->thread.ppr = INIT_PPR;

tools/testing/selftests/powerpc/dscr/dscr_inherit_exec_test.c +0 -8

index 8265504..08a8b95 100644
@@ -60,14 +60,6 @@ int dscr_inherit_exec(void)
 		else
 			set_dscr(dscr);
 
-		/*
-		 * XXX: Force a context switch out so that DSCR
-		 * current value is copied into the thread struct
-		 * which is required for the child to inherit the
-		 * changed value.
-		 */
-		sleep(1);
-
 		pid = fork();
 		if (pid == -1) {
 			perror("fork() failed");

tools/testing/selftests/powerpc/dscr/dscr_inherit_test.c +0 -8

index 4e414ca..3e5a6d1 100644
@@ -40,14 +40,6 @@ int dscr_inherit(void)
 		else
 			set_dscr(dscr);
 
-		/*
-		 * XXX: Force a context switch out so that DSCR
-		 * current value is copied into the thread struct
-		 * which is required for the child to inherit the
-		 * changed value.
-		 */
-		sleep(1);
-
 		pid = fork();
 		if (pid == -1) {
 			perror("fork() failed");

Signature · 1 line

2.5.0

Michael Ellerman

reviewer Applied

2015-12-14 09:47 UTC #1 lore raw

Quoted 10 lines · Anton Blanchard

Two DSCR tests have a hack in them:
/*
* XXX: Force a context switch out so that DSCR
* current value is copied into the thread struct
* which is required for the child to inherit the
* changed value.
*/
sleep(1);

Quoted 5 lines

We should not be working around this in the testcase, it is a kernel bug. Fix it by copying the current DSCR to the child, instead of what we had in the thread struct at last context switch.
Signed-off-by Anton Blanchard <[email protected]>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/db1231dcdb4dc6cdcbdef0ba

cheers