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Subject[PATCH] arm64: break while loop if task had been rescheduled
Date
While printing a task's backtrace and this task isn't
current task, it is possible that task's fp and fp+8
have the same value, so cannot break the while loop.
This can break while loop if this task had been
rescheduled during print this task's backtrace.

Signed-off-by: Tengfei Fan <tengfeif@codeaurora.org>
---
arch/arm64/kernel/traps.c | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)

diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 2975598..9df6e02 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -103,6 +103,9 @@ void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
{
struct stackframe frame;
int skip = 0;
+ long cur_state = 0;
+ unsigned long cur_sp = 0;
+ unsigned long cur_fp = 0;

pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);

@@ -127,6 +130,9 @@ void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
*/
frame.fp = thread_saved_fp(tsk);
frame.pc = thread_saved_pc(tsk);
+ cur_state = tsk->state;
+ cur_sp = thread_saved_sp(tsk);
+ cur_fp = frame.fp;
}
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
frame.graph = 0;
@@ -134,6 +140,23 @@ void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)

printk("Call trace:\n");
do {
+ if (tsk != current && (cur_state != tsk->state
+ /*
+ * We would not be printing backtrace for the task
+ * that has changed state from uninterruptible to
+ * running before hitting the do-while loop but after
+ * saving the current state. If task is in running
+ * state before saving the state, then we may print
+ * wrong call trace or end up in infinite while loop
+ * if *(fp) and *(fp+8) are same. While the situation
+ * will stop print when that task schedule out.
+ */
+ || cur_sp != thread_saved_sp(tsk)
+ || cur_fp != thread_saved_fp(tsk))) {
+ printk("The task:%s had been rescheduled!\n",
+ tsk->comm);
+ break;
+ }
/* skip until specified stack frame */
if (!skip) {
dump_backtrace_entry(frame.pc);
--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project
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