s390/unwind: stop gracefully at task pt_regs

Consider reaching task pt_regs graceful unwinder termination. Task
pt_regs itself never contains a valid state to which a task might return
within the kernel context (user task pt_regs is a special case). Since
we already avoid printing user task pt_regs and in most cases we don't
even bother filling task pt_regs psw and r15 with something reasonable
simply skip task pt_regs altogether. With this change unwind_error() now
accurately represent whether unwinder reached task pt_regs successfully
or failed along the way.

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

diff --git a/arch/s390/kernel/unwind_bc.c b/arch/s390/kernel/unwind_bc.c
index ac6cfab567d189eadacd67036d43b416402d8cf1..c5ebb8a4cdd6d676612c157364b57c5df29c181e 100644 (file)
--- a/arch/s390/kernel/unwind_bc.c
+++ b/arch/s390/kernel/unwind_bc.c
@@ -36,6 +36,12 @@ static bool update_stack_info(struct unwind_state *state, unsigned long sp)
        return true;
 }
 
+static inline bool is_task_pt_regs(struct unwind_state *state,
+                                  struct pt_regs *regs)
+{
+       return task_pt_regs(state->task) == regs;
+}
+
 bool unwind_next_frame(struct unwind_state *state)
 {
        struct stack_info *info = &state->stack_info;
@@ -69,7 +75,7 @@ bool unwind_next_frame(struct unwind_state *state)
                        if (!on_stack(info, sp, sizeof(struct pt_regs)))
                                goto out_err;
                        regs = (struct pt_regs *) sp;
-                       if (READ_ONCE_NOCHECK(regs->psw.mask) & PSW_MASK_PSTATE)
+                       if (is_task_pt_regs(state, regs))
                                goto out_stop;
                        ip = READ_ONCE_NOCHECK(regs->psw.addr);
                        sp = READ_ONCE_NOCHECK(regs->gprs[15]);