Commit 97806dfb authored by Vasily Gorbik's avatar Vasily Gorbik
Browse files

s390/unwind: make reuse_sp default when unwinding pt_regs 



Currently unwinder yields 2 entries when pt_regs are met:
sp="address of pt_regs itself" ip=pt_regs->psw
sp=pt_regs->gprs[15] ip="r14 from stack frame pointed by pt_regs->gprs[15]"

And neither of those 2 states (combination of sp and ip) ever happened.

reuse_sp has been introduced by commit a1d863ac ("s390/unwind: fix
mixing regs and sp"). reuse_sp=true makes unwinder keen to produce the
following result, when pt_regs are given (as an arg to unwind_start):
sp=pt_regs->gprs[15] ip=pt_regs->psw
sp=pt_regs->gprs[15] ip="r14 from stack frame pointed by pt_regs->gprs[15]"

The first state is an actual state in which a task was when pt_regs were
collected. The second state is marked unreliable and is for debugging
purposes to cover the case when a task has been interrupted in between
stack frame allocation and writing back_chain - in this case r14 might
show an actual caller.

Make unwinder behaviour enabled via reuse_sp=true default and drop the
special case handling.

Reviewed-by: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: default avatarVasily Gorbik <gor@linux.ibm.com>
parent 67f55934

arch/s390/include/asm/unwind.h

+0 −1
Original line number Diff line number Diff line
@@ -35,7 +35,6 @@ struct unwind_state { 
	struct task_struct *task;

	struct pt_regs *regs;

	unsigned long sp, ip;

	bool reuse_sp;

	int graph_idx;

	bool reliable;

	bool error;

arch/s390/kernel/unwind_bc.c

+7 −14
Original line number Diff line number Diff line
@@ -46,16 +46,7 @@ bool unwind_next_frame(struct unwind_state *state) 


	regs = state->regs;

	if (unlikely(regs)) {

		if (state->reuse_sp) {

		sp = state->sp;

			state->reuse_sp = false;

		} else {

			sp = READ_ONCE_NOCHECK(regs->gprs[15]);

			if (unlikely(outside_of_stack(state, sp))) {

				if (!update_stack_info(state, sp))

					goto out_err;

			}

		}

		sf = (struct stack_frame *) sp;

		ip = READ_ONCE_NOCHECK(sf->gprs[8]);

		reliable = false;
@@ -81,6 +72,11 @@ bool unwind_next_frame(struct unwind_state *state) 
			if (READ_ONCE_NOCHECK(regs->psw.mask) & PSW_MASK_PSTATE)

				goto out_stop;

			ip = READ_ONCE_NOCHECK(regs->psw.addr);

			sp = READ_ONCE_NOCHECK(regs->gprs[15]);

			if (unlikely(outside_of_stack(state, sp))) {

				if (!update_stack_info(state, sp))

					goto out_err;

			}

			reliable = true;

		}

	}
@@ -107,7 +103,7 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task, 
{

	struct stack_info *info = &state->stack_info;

	unsigned long *mask = &state->stack_mask;

	bool reliable, reuse_sp;

	bool reliable;

	struct stack_frame *sf;

	unsigned long ip;
@@ -134,12 +130,10 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task, 
	if (regs) {

		ip = READ_ONCE_NOCHECK(regs->psw.addr);

		reliable = true;

		reuse_sp = true;

	} else {

		sf = (struct stack_frame *) sp;

		ip = READ_ONCE_NOCHECK(sf->gprs[8]);

		reliable = false;

		reuse_sp = false;

	}



	ip = ftrace_graph_ret_addr(state->task, &state->graph_idx, ip, NULL);
@@ -148,6 +142,5 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task, 
	state->sp = sp;

	state->ip = ip;

	state->reliable = reliable;

	state->reuse_sp = reuse_sp;

}

EXPORT_SYMBOL_GPL(__unwind_start);