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 a1d863ac3e10 ("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: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

1 files changed, 0 insertions, 1 deletions

diff --git a/arch/s390/include/asm/unwind.h b/arch/s390/include/asm/unwind.h
index a2d8dd766987..5d6c8fe7a271 100644
--- a/arch/s390/include/asm/unwind.h
+++ b/arch/s390/include/asm/unwind.h
@@ -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;