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Subject[PATCH v3 4/4] arm64: reliable stacktraces
Date
From
Make unwind_frame() report whether it had to stop normally or due to
an error condition; walk_stackframe() will pass that info.
__save_stack_trace() is used to check the validity of a frame;
save_stack_trace_tsk_reliable() can now trivially be implemented.
Modify arch/arm64/kernel/time.c for the new semantics.

Signed-off-by: Torsten Duwe <duwe@suse.de>

--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -127,8 +127,9 @@ config ARM64
select HAVE_PERF_EVENTS
select HAVE_PERF_REGS
select HAVE_PERF_USER_STACK_DUMP
- select HAVE_REGS_AND_STACK_ACCESS_API
select HAVE_RCU_TABLE_FREE
+ select HAVE_REGS_AND_STACK_ACCESS_API
+ select HAVE_RELIABLE_STACKTRACE
select HAVE_STACKPROTECTOR
select HAVE_SYSCALL_TRACEPOINTS
select HAVE_KPROBES
--- a/arch/arm64/include/asm/stacktrace.h
+++ b/arch/arm64/include/asm/stacktrace.h
@@ -33,7 +33,7 @@ struct stackframe {
};

extern int unwind_frame(struct task_struct *tsk, struct stackframe *frame);
-extern void walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
+extern int walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
int (*fn)(struct stackframe *, void *), void *data);
extern void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk);

--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -40,6 +40,13 @@
* ldp x29, x30, [sp]
* add sp, sp, #0x10
*/
+
+/*
+ * unwind_frame -- unwind a single stack frame.
+ * Returns 0 when there are more frames to go.
+ * 1 means reached end of stack; negative (error)
+ * means stopped because information is not reliable.
+ */
int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
{
unsigned long fp = frame->fp;
@@ -81,23 +88,27 @@ int notrace unwind_frame(struct task_str
* both are NULL.
*/
if (!frame->fp && !frame->pc)
- return -EINVAL;
+ return 1;

return 0;
}

-void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
+int notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
int (*fn)(struct stackframe *, void *), void *data)
{
while (1) {
int ret;

- if (fn(frame, data))
- break;
+ ret = fn(frame, data);
+ if (ret)
+ return ret;
ret = unwind_frame(tsk, frame);
if (ret < 0)
+ return ret;
+ if (ret > 0)
break;
}
+ return 0;
}

#ifdef CONFIG_STACKTRACE
@@ -145,14 +156,15 @@ void save_stack_trace_regs(struct pt_reg
trace->entries[trace->nr_entries++] = ULONG_MAX;
}

-static noinline void __save_stack_trace(struct task_struct *tsk,
+static noinline int __save_stack_trace(struct task_struct *tsk,
struct stack_trace *trace, unsigned int nosched)
{
struct stack_trace_data data;
struct stackframe frame;
+ int ret;

if (!try_get_task_stack(tsk))
- return;
+ return -EBUSY;

data.trace = trace;
data.skip = trace->skip;
@@ -171,11 +183,12 @@ static noinline void __save_stack_trace(
frame.graph = tsk->curr_ret_stack;
#endif

- walk_stackframe(tsk, &frame, save_trace, &data);
+ ret = walk_stackframe(tsk, &frame, save_trace, &data);
if (trace->nr_entries < trace->max_entries)
trace->entries[trace->nr_entries++] = ULONG_MAX;

put_task_stack(tsk);
+ return ret;
}
EXPORT_SYMBOL_GPL(save_stack_trace_tsk);

@@ -190,4 +203,12 @@ void save_stack_trace(struct stack_trace
}

EXPORT_SYMBOL_GPL(save_stack_trace);
+
+int save_stack_trace_tsk_reliable(struct task_struct *tsk,
+ struct stack_trace *trace)
+{
+ return __save_stack_trace(tsk, trace, 1);
+}
+EXPORT_SYMBOL_GPL(save_stack_trace_tsk_reliable);
+
#endif
--- a/arch/arm64/kernel/time.c
+++ b/arch/arm64/kernel/time.c
@@ -56,7 +56,7 @@ unsigned long profile_pc(struct pt_regs
#endif
do {
int ret = unwind_frame(NULL, &frame);
- if (ret < 0)
+ if (ret)
return 0;
} while (in_lock_functions(frame.pc));

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