From: Josh Poimboeuf jpoimboe@redhat.com
commit 187b96db5ca79423618dfa29a05c438c34f9e1f0 upstream.
Normally, show_trace_log_lvl() scans the stack, looking for text addresses to print. In parallel, it unwinds the stack with unwind_next_frame(). If the stack address matches the pointer returned by unwind_get_return_address_ptr() for the current frame, the text address is printed normally without a question mark. Otherwise it's considered a breadcrumb (potentially from a previous call path) and it's printed with a question mark to indicate that the address is unreliable and typically can be ignored.
Since the following commit:
f1d9a2abff66 ("x86/unwind/orc: Don't skip the first frame for inactive tasks")
... for inactive tasks, show_trace_log_lvl() prints *only* unreliable addresses (prepended with '?').
That happens because, for the first frame of an inactive task, unwind_get_return_address_ptr() returns the wrong return address pointer: one word *below* the task stack pointer. show_trace_log_lvl() starts scanning at the stack pointer itself, so it never finds the first 'reliable' address, causing only guesses to being printed.
The first frame of an inactive task isn't a normal stack frame. It's actually just an instance of 'struct inactive_task_frame' which is left behind by __switch_to_asm(). Now that this inactive frame is actually exposed to callers, fix unwind_get_return_address_ptr() to interpret it properly.
Fixes: f1d9a2abff66 ("x86/unwind/orc: Don't skip the first frame for inactive tasks") Reported-by: Tetsuo Handa penguin-kernel@i-love.sakura.ne.jp Signed-off-by: Josh Poimboeuf jpoimboe@redhat.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lkml.kernel.org/r/20200522135435.vbxs7umku5pyrdbk@treble Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kernel/unwind_orc.c | 7 +++++++ 1 file changed, 7 insertions(+)
--- a/arch/x86/kernel/unwind_orc.c +++ b/arch/x86/kernel/unwind_orc.c @@ -255,12 +255,19 @@ EXPORT_SYMBOL_GPL(unwind_get_return_addr
unsigned long *unwind_get_return_address_ptr(struct unwind_state *state) { + struct task_struct *task = state->task; + if (unwind_done(state)) return NULL;
if (state->regs) return &state->regs->ip;
+ if (task != current && state->sp == task->thread.sp) { + struct inactive_task_frame *frame = (void *)task->thread.sp; + return &frame->ret_addr; + } + if (state->sp) return (unsigned long *)state->sp - 1;