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: 1149aad10b1e ("arm64: Add dump_backtrace() in show_regs")
Reported-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 9 insertions, 6 deletions

diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 8ad119c3f665..29755989f616 100644
--- 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;
 }