lkml.org 
[lkml]   [2020]   [Jun]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: kprobe: __blkdev_put probe is missed
Hi Ming,

On Thu, 18 Jun 2020 20:54:38 +0800
Ming Lei <ming.lei@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 <mhiramat@kernel.org>

\
 
 \ /
  Last update: 2020-06-18 15:56    [W:0.076 / U:0.244 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site