x86/unwind: Include __schedule() in stack traces

In the following commit:

  0100301bfdf5 ("sched/x86: Rewrite the switch_to() code")

... the layout of the 'inactive_task_frame' struct was designed to have
a frame pointer header embedded in it, so that the unwinder could use
the 'bp' and 'ret_addr' fields to report __schedule() on the stack (or
ret_from_fork() for newly forked tasks which haven't actually run yet).

Finish the job by changing get_frame_pointer() to return a pointer to
inactive_task_frame's 'bp' field rather than 'bp' itself.  This allows
the unwinder to start one frame higher on the stack, so that it properly
reports __schedule().

Reported-by: Miroslav Benes <[email protected]>
Signed-off-by: Josh Poimboeuf <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Dave Jones <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/598e9f7505ed0aba86e8b9590aa528c6c7ae8dcd.1483978430.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/arch/x86/include/asm/stacktrace.h b/arch/x86/include/asm/stacktrace.h
index 20ce3db20f24f1a9d0fae9d481327ab023ce318a..2e41c50ddf47f414c8f2e4b0a99965ceafffb4bf 100644 (file)
--- a/arch/x86/include/asm/stacktrace.h
+++ b/arch/x86/include/asm/stacktrace.h
@@ -52,16 +52,13 @@ static inline bool on_stack(struct stack_info *info, void *addr, size_t len)
 static inline unsigned long *
 get_frame_pointer(struct task_struct *task, struct pt_regs *regs)
 {
-       struct inactive_task_frame *frame;
-
        if (regs)
                return (unsigned long *)regs->bp;
 
        if (task == current)
                return __builtin_frame_address(0);
 
-       frame = (struct inactive_task_frame *)task->thread.sp;
-       return (unsigned long *)READ_ONCE_NOCHECK(frame->bp);
+       return &((struct inactive_task_frame *)task->thread.sp)->bp;
 }
 #else
 static inline unsigned long *

diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h
index 5cb436acd46315b75ba40aacc780373ea2cc4f7c..fcc5cd387fd17a59e5f28ba5fc8fb65fc57ae5af 100644 (file)
--- a/arch/x86/include/asm/switch_to.h
+++ b/arch/x86/include/asm/switch_to.h
@@ -36,7 +36,10 @@ static inline void prepare_switch_to(struct task_struct *prev,
 
 asmlinkage void ret_from_fork(void);
 
-/* data that is pointed to by thread.sp */
+/*
+ * This is the structure pointed to by thread.sp for an inactive task.  The
+ * order of the fields must match the code in __switch_to_asm().
+ */
 struct inactive_task_frame {
 #ifdef CONFIG_X86_64
        unsigned long r15;
@@ -48,6 +51,11 @@ struct inactive_task_frame {
        unsigned long di;
 #endif
        unsigned long bx;
+
+       /*
+        * These two fields must be together.  They form a stack frame header,
+        * needed by get_frame_pointer().
+        */
        unsigned long bp;
        unsigned long ret_addr;
 };