arm64: backtrace: Don't bother trying to unwind the userspace stack

Calling dump_backtrace() with a pt_regs argument corresponding to
userspace doesn't make any sense and our unwinder will simply print
"Call trace:" before unwinding the stack looking for user frames.

Rather than go through this song and dance, just return early if we're
passed a user register state.

Cc: <stable@vger.kernel.org>
Fixes: 6f9bcfcf217e ("arm64: Add dump_backtrace() in show_regs")
Reported-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 8ad119c3f665d4e8001038ccf3bd6dcb62e2e224..29755989f616c187481803b27ca9dbfcf0a7847b 100644 (file)
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -102,10 +102,16 @@ static void dump_instr(const char *lvl, struct pt_regs *regs)
 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
 {
        struct stackframe frame;
-       int skip;
+       int skip = 0;
 
        pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
 
+       if (regs) {
+               if (user_mode(regs))
+                       return;
+               skip = 1;
+       }
+
        if (!tsk)
                tsk = current;
 
@@ -126,7 +132,6 @@ void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
        frame.graph = 0;
 #endif
 
-       skip = !!regs;
        printk("Call trace:\n");
        do {
                /* skip until specified stack frame */
@@ -176,15 +181,13 @@ static int __die(const char *str, int err, struct pt_regs *regs)
                return ret;
 
        print_modules();
-       __show_regs(regs);
        pr_emerg("Process %.*s (pid: %d, stack limit = 0x%p)\n",
                 TASK_COMM_LEN, tsk->comm, task_pid_nr(tsk),
                 end_of_stack(tsk));
+       show_regs(regs);
 
-       if (!user_mode(regs)) {
-               dump_backtrace(regs, tsk);
+       if (!user_mode(regs))
                dump_instr(KERN_EMERG, regs);
-       }
 
        return ret;
 }