Powerpc hw triggers watchpoint before executing the instruction. To make trigger-after-execute behavior, kernel emulates the instruction. If the instruction is 'load something into non- volatile register', exception handler should restore emulated register state while returning back, otherwise there will be register state corruption. Ex, Adding a watchpoint on a list can corrput the list:
# cat /proc/kallsyms | grep kthread_create_list c00000000121c8b8 d kthread_create_list Add watchpoint on kthread_create_list->next: # perf record -e mem:0xc00000000121c8c0 Run some workload such that new kthread gets invoked. Ex, I just logged out from console: list_add corruption. next->prev should be prev (c000000001214e00), \ but was c00000000121c8b8. (next=c00000000121c8b8). WARNING: CPU: 59 PID: 309 at lib/list_debug.c:25 __list_add_valid+0xb4/0xc0 CPU: 59 PID: 309 Comm: kworker/59:0 Kdump: loaded Not tainted 5.1.0-rc7+ #69 ... NIP __list_add_valid+0xb4/0xc0 LR __list_add_valid+0xb0/0xc0 Call Trace: __list_add_valid+0xb0/0xc0 (unreliable) __kthread_create_on_node+0xe0/0x260 kthread_create_on_node+0x34/0x50 create_worker+0xe8/0x260 worker_thread+0x444/0x560 kthread+0x160/0x1a0 ret_from_kernel_thread+0x5c/0x70 Signed-off-by: Ravi Bangoria <ravi.bango...@linux.ibm.com> --- arch/powerpc/kernel/exceptions-64s.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S index 9481a11..96de0d1 100644 --- a/arch/powerpc/kernel/exceptions-64s.S +++ b/arch/powerpc/kernel/exceptions-64s.S @@ -1753,7 +1753,7 @@ handle_dabr_fault: ld r5,_DSISR(r1) addi r3,r1,STACK_FRAME_OVERHEAD bl do_break -12: b ret_from_except_lite +12: b ret_from_except #ifdef CONFIG_PPC_BOOK3S_64 -- 1.8.3.1