Re: [PATCH] arm64: avoid race condition issue in dump_backtrace

From: kbuild test robot
Date: Sat Mar 24 2018 - 07:03:01 EST


Hi Ji,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on arm64/for-next/core]
[also build test ERROR on v4.16-rc6 next-20180323]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url: https://github.com/0day-ci/linux/commits/Ji-Zhang/arm64-avoid-race-condition-issue-in-dump_backtrace/20180324-165040
base: https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-next/core
config: arm64-defconfig (attached as .config)
compiler: aarch64-linux-gnu-gcc (Debian 7.2.0-11) 7.2.0
reproduce:
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# save the attached .config to linux build tree
make.cross ARCH=arm64

All errors (new ones prefixed by >>):

arch/arm64/kernel/traps.c: In function 'dump_backtrace':
>> arch/arm64/kernel/traps.c:116:2: error: expected '}' before 'else'
else if (tsk->state == TASK_RUNNING) {
^~~~

vim +116 arch/arm64/kernel/traps.c

99
100 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
101 {
102 struct stackframe frame;
103 int skip;
104
105 pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
106
107 if (!tsk)
108 tsk = current;
109
110 if (!try_get_task_stack(tsk))
111 return;
112
113 if (tsk == current) {
114 frame.fp = (unsigned long)__builtin_frame_address(0);
115 frame.pc = (unsigned long)dump_backtrace;
> 116 else if (tsk->state == TASK_RUNNING) {
117 pr_notice("Do not dump other running tasks\n");
118 return;
119 } else {
120 /*
121 * task blocked in __switch_to
122 */
123 frame.fp = thread_saved_fp(tsk);
124 frame.pc = thread_saved_pc(tsk);
125 }
126 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
127 frame.graph = tsk->curr_ret_stack;
128 #endif
129
130 skip = !!regs;
131 printk("Call trace:\n");
132 do {
133 /* skip until specified stack frame */
134 if (!skip) {
135 dump_backtrace_entry(frame.pc);
136 } else if (frame.fp == regs->regs[29]) {
137 skip = 0;
138 /*
139 * Mostly, this is the case where this function is
140 * called in panic/abort. As exception handler's
141 * stack frame does not contain the corresponding pc
142 * at which an exception has taken place, use regs->pc
143 * instead.
144 */
145 dump_backtrace_entry(regs->pc);
146 }
147 } while (!unwind_frame(tsk, &frame));
148
149 put_task_stack(tsk);
150 }
151

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