Hi Ming,
On Thu, 18 Jun 2020 20:54:38 +0800
Ming Lei <ming....@redhat.com> wrote:
> On Wed, Jun 17, 2020 at 06:30:39PM +0800, Ming Lei wrote:
> > 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
Could you dump the kprobe_event as below?
# cat /sys/kernel/tracing/kprobe_events
> >
> > or
> >
> > /usr/share/bcc/tools/stackcount __blkdev_put
> >
> > 2) run the following command:
> > blockdev --getbsz /dev/sda1
And dump the kprobe profile?
# cat /sys/kernel/tracing/kprobe_profile
> >
> > 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 issue can be shown by loading a kprobe module which registers on
> __blkdev_put(), just by replacing _do_fork with __blkdev_put on
> samples/kprobes/kprobe_example.c.
Could you tell me what kernel are you using?
I'm using 5.4 on ubuntu and can not reproduce it with kprobe_event.
root@devnote2:/sys/kernel/tracing# uname -a
Linux devnote2 5.4.0-37-generic #41-Ubuntu SMP Wed Jun 3 18:57:02 UTC 2020
x86_64 x86_64 x86_64 GNU/Linux
root@devnote2:/sys/kernel/tracing# echo p __blkdev_put > kprobe_events
root@devnote2:/sys/kernel/tracing# echo 1 >
events/kprobes/p___blkdev_put_0/enable
root@devnote2:/sys/kernel/tracing# cat trace
# tracer: nop
#
# entries-in-buffer/entries-written: 0/0 #P:8
#
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
root@devnote2:/sys/kernel/tracing# blockdev --getbsz /dev/nvme0n1
4096
root@devnote2:/sys/kernel/tracing# cat trace
# tracer: nop
#
# entries-in-buffer/entries-written: 1/1 #P:8
#
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
<...>-111740 [002] .... 301734.476991: p___blkdev_put_0:
(__blkdev_put+0x0/0x1e0)
Hmm, maybe some issue in the latest kernel...?
Thank you,
--
Masami Hiramatsu <mhira...@kernel.org>
