x86/stacktrace: Avoid recording save_stack_trace() wrappers

tehcaster · Ingo Molnar · commit 77072f09eab1 · 2017-09-29T19:44:03.000+02:00
The save_stack_trace() and save_stack_trace_tsk() wrappers of __save_stack_trace() add themselves to the call stack, and thus appear in the recorded stacktraces. This is redundant and wasteful when we have limited space to record the useful part of the backtrace with e.g. page_owner functionality. Fix this by making sure __save_stack_trace() is noinline (which matches the current gcc decision) and bumping the skip in the wrappers (save_stack_trace_tsk() only when called for the current task). This is similar to what was done for arm in 3683f44 ("ARM: stacktrace: avoid listing stacktrace functions in stacktrace") and is pending for arm64. Also make sure that __save_stack_trace_reliable() doesn't get this problem in the future by marking it __always_inline (which matches current gcc decision), per Josh Poimboeuf. Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Acked-by: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Miroslav Benes <mbenes@suse.cz> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/20170929092335.2744-1-vbabka@suse.cz Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c
@@ -30,7 +30,7 @@ static int save_stack_address(struct stack_trace *trace, unsigned long addr,
 	return 0;
 }
 
-static void __save_stack_trace(struct stack_trace *trace,
+static void noinline __save_stack_trace(struct stack_trace *trace,
 			       struct task_struct *task, struct pt_regs *regs,
 			       bool nosched)
 {
@@ -56,6 +56,7 @@ static void __save_stack_trace(struct stack_trace *trace,
  */
 void save_stack_trace(struct stack_trace *trace)
 {
+	trace->skip++;
 	__save_stack_trace(trace, current, NULL, false);
 }
 EXPORT_SYMBOL_GPL(save_stack_trace);
@@ -70,6 +71,8 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
 	if (!try_get_task_stack(tsk))
 		return;
 
+	if (tsk == current)
+		trace->skip++;
 	__save_stack_trace(trace, tsk, NULL, true);
 
 	put_task_stack(tsk);
@@ -88,8 +91,9 @@ EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
 	}							\
 })
 
-static int __save_stack_trace_reliable(struct stack_trace *trace,
-				       struct task_struct *task)
+static int __always_inline
+__save_stack_trace_reliable(struct stack_trace *trace,
+			    struct task_struct *task)
 {
 	struct unwind_state state;
 	struct pt_regs *regs;
