[PATCH RFC] Btrfs: fix confusing worker helper info

[PATCH RFC] Btrfs: fix confusing worker helper info

[Liu Bo]

We've seen the following backtrace stack in ftrace or dmesg log,

  kworker/u16:10-4244  [000] 241942.480955: function:             btrfs_put_ordered_extent
  kworker/u16:10-4244  [000] 241942.480956: kernel_stack:         <stack trace>
=> finish_ordered_fn (ffffffffa0384475)
=> btrfs_scrubparity_helper (ffffffffa03ca577)
=> btrfs_freespace_write_helper (ffffffffa03ca98e)
=> process_one_work (ffffffff81117b2f)
=> worker_thread (ffffffff81118c2a)
=> kthread (ffffffff81121de0)
=> ret_from_fork (ffffffff81d7087a)

btrfs_scrubparity_helper really shouldn't be shown up.

It's caused by compiler doing inline for our helper function, adding a
noinline tag can fix that.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
---
 fs/btrfs/async-thread.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/async-thread.c b/fs/btrfs/async-thread.c
index ff0b0be..593709a 100644
--- a/fs/btrfs/async-thread.c
+++ b/fs/btrfs/async-thread.c
@@ -67,7 +67,7 @@ struct btrfs_workqueue {
 static void normal_work_helper(struct btrfs_work *work);
 
 #define BTRFS_WORK_HELPER(name)					\
-void btrfs_##name(struct work_struct *arg)				\
+noinline void btrfs_##name(struct work_struct *arg)			\
 {									\
 	struct btrfs_work *work = container_of(arg, struct btrfs_work,	\
 					       normal_work);		\
-- 
2.9.4

Re: [PATCH RFC] Btrfs: fix confusing worker helper info

[David Sterba]

On Fri, Sep 08, 2017 at 03:34:45PM -0600, Liu Bo wrote:
> We've seen the following backtrace stack in ftrace or dmesg log,
> 
>   kworker/u16:10-4244  [000] 241942.480955: function:             btrfs_put_ordered_extent
>   kworker/u16:10-4244  [000] 241942.480956: kernel_stack:         <stack trace>
> => finish_ordered_fn (ffffffffa0384475)
> => btrfs_scrubparity_helper (ffffffffa03ca577)
> => btrfs_freespace_write_helper (ffffffffa03ca98e)
> => process_one_work (ffffffff81117b2f)
> => worker_thread (ffffffff81118c2a)
> => kthread (ffffffff81121de0)
> => ret_from_fork (ffffffff81d7087a)
> 
> btrfs_scrubparity_helper really shouldn't be shown up.
> 
> It's caused by compiler doing inline for our helper function, adding a
> noinline tag can fix that.

Isn't it the other way around then? Noninline would make the function
object exist separately and then it would appear in the stacktrace. And
I think this is desired, so you see the call stack withtou the shortcuts
that the inlining can cause.