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Subject[PATCH] stacktrace: fix CONFIG_ARCH_STACKWALK stack_trace_save_tsk_reliable return
Date
Miroslav reported that the livepatch self-tests were failing,
specifically a case in which the consistency model ensures that we do
not patch a current executing function, "TEST: busy target module".

Recent renovations to stack_trace_save_tsk_reliable() left it returning
only an -ERRNO success indication in some configuration combinations:

klp_check_stack()
ret = stack_trace_save_tsk_reliable()
#ifdef CONFIG_ARCH_STACKWALK && CONFIG_HAVE_RELIABLE_STACKTRACE
stack_trace_save_tsk_reliable()
ret = arch_stack_walk_reliable()
return 0
return -EINVAL
...
return ret;
...
if (ret < 0)
/* stack_trace_save_tsk_reliable error */
nr_entries = ret; << 0

Previously (and currently for !CONFIG_ARCH_STACKWALK &&
CONFIG_HAVE_RELIABLE_STACKTRACE) stack_trace_save_tsk_reliable()
returned the number of entries that it consumed in the passed storage
array.

In the case of the above config and trace, be sure to return the
stacktrace_cookie.len on stack_trace_save_tsk_reliable() success.

Fixes: 25e39e32b0a3f ("livepatch: Simplify stack trace retrieval")
Reported-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
---
kernel/stacktrace.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
index 27bafc1e271e..90d3e0bf0302 100644
--- a/kernel/stacktrace.c
+++ b/kernel/stacktrace.c
@@ -206,7 +206,7 @@ int stack_trace_save_tsk_reliable(struct task_struct *tsk, unsigned long *store,

ret = arch_stack_walk_reliable(consume_entry, &c, tsk);
put_task_stack(tsk);
- return ret;
+ return ret ? ret : c.len;
}
#endif

--
2.20.1
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