powerpc: Fix MAX_STACK_TRACE_ENTRIES too low warning again

Saw this warning again, and this time from the ret_from_fork path.

It seems we could clear the back chain earlier in copy_thread(), which
could cover both path, and also fix potential lockdep usage in
schedule_tail(), or exception occurred before we clear the back chain.

Signed-off-by: Li Zhong <zhong@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

3 files changed, 1 insertions, 4 deletions

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index e514de57a125..d22e73e4618b 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -439,8 +439,6 @@ ret_from_fork:
 ret_from_kernel_thread:
         REST_NVGPRS(r1)
         bl      schedule_tail
-        li      r3,0
-        stw     r3,0(r1)
         mtlr    r14
         mr      r3,r15
         PPC440EP_ERR42
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 3fe5259e2fea..48e8a86e7cb2 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -376,8 +376,6 @@ _GLOBAL(ret_from_fork)
 _GLOBAL(ret_from_kernel_thread)
         bl      .schedule_tail
         REST_NVGPRS(r1)
-        li      r3,0
-        std     r3,0(r1)
         ld      r14, 0(r14)
         mtlr    r14
         mr      r3,r15
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index ceb4e7b62cf4..21981a89e394 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -971,6 +971,7 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
          * do some house keeping and then return from the fork or clone
          * system call, using the stack frame created above.
          */
+        ((unsigned long *)sp)[0] = 0;
         sp -= sizeof(struct pt_regs);
         kregs = (struct pt_regs *) sp;
         sp -= STACK_FRAME_OVERHEAD;