krobe: __blkdev_put probe is missed

[Ming Lei]

Hello Guys,

I found probe on __blkdev_put is missed, which can be observed
via bcc/perf reliably:

1) start trace
- perf probe __blkdev_put
- perf trace -a  -e probe:__blkdev_put

or

/usr/share/bcc/tools/stackcount __blkdev_put

2) run the following command:
blockdev --getbsz /dev/sda1

3) 'perf trace'  or stackcount just  dumps one trace event, and it
should have been two
__blkdev_put() traces, since one __blkdev_put() is called for
partition(/dev/sda1),
and another is for disk(/dev/sda). If trace_printk() is added in __blkdev_put(),
two events will be captured from ftrace.

The only special thing about __blkdev_put() is that the function will call into
itself. However, no such issue on __blkdev_get() which calls itself too.


Thanks,
Ming Lei