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Message-ID: <20200619072859.GA205278@T590>
Date: Fri, 19 Jun 2020 15:28:59 +0800
From: Ming Lei <ming.lei@...hat.com>
To: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Ming Lei <tom.leiming@...il.com>,
"Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
"David S. Miller" <davem@...emloft.net>,
Steven Rostedt <rostedt@...dmis.org>,
linux-block <linux-block@...r.kernel.org>
Subject: Re: kprobe: __blkdev_put probe is missed
Hi Masami,
On Fri, Jun 19, 2020 at 02:12:39PM +0900, Masami Hiramatsu wrote:
> Hi Ming,
>
> On Fri, 19 Jun 2020 07:19:01 +0800
> Ming Lei <ming.lei@...hat.com> wrote:
>
> > > I'm using 5.4 on ubuntu and can not reproduce it with kprobe_event.
> > >
> > > root@...note2:/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@...note2:/sys/kernel/tracing# echo p __blkdev_put > kprobe_events
> > > root@...note2:/sys/kernel/tracing# echo 1 > events/kprobes/p___blkdev_put_0/enable
> > > root@...note2:/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@...note2:/sys/kernel/tracing# blockdev --getbsz /dev/nvme0n1
> > > 4096
> > > root@...note2:/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...?
> >
> > Hello Masami,
> >
> > I am testing the latest upstream kernel, your trace actually reproduces
> > this issue.
>
> OK.
>
> >
> > After 'blockdev --getbsz /dev/nvme0n1' returns, __blkdev_put() should
> > have been called two times(one for partition, and the other for disk),
> > however kprobe trace just shows one time of calling this function.
> >
> > If trace_printk() is added at the entry of __blkdev_put() manually,
> > you will see that __blkdev_put() is called two times in 'blockdev
> > --getbsz /dev/nvme0n1'.
>
> OK, let me check again on the latest kernel.
> Here I tested with qemu.
>
> root@...note2:/sys/kernel/debug/tracing# uname -a
> Linux devnote2 5.8.0-rc1+ #26 SMP PREEMPT Fri Jun 19 12:12:53 JST 2020 x86_64 x86_64 x86_64 GNU/Linux
>
> And we have a (virtual) sda with 1 partition.
>
> root@...note2:/sys/kernel/debug/tracing# cat /proc/partitions
> major minor #blocks name
>
> 8 0 10240 sda
> 8 1 9216 sda1
>
> OK, then let's make events (for sure)
>
> root@...note2:/sys/kernel/debug/tracing# echo p __blkdev_put >> kprobe_events
> root@...note2:/sys/kernel/debug/tracing# echo r __blkdev_put >> kprobe_events
> root@...note2:/sys/kernel/debug/tracing# echo p blkdev_put >> kprobe_events
>
> There are 3 events in the kernel, blkdev_put() and __blkdev_put() and
> the return of __blkdev_put().
> Then enable it and access to */dev/sda* (a disk)
>
> root@...note2:/sys/kernel/debug/tracing# echo 1 > events/kprobes/enable
> root@...note2:/sys/kernel/debug/tracing# blockdev --getbsz /dev/sda
> 4096
> root@...note2:/sys/kernel/debug/tracing# echo 0 > events/kprobes/enable
> root@...note2:/sys/kernel/debug/tracing# cat trace
> # tracer: nop
> #
> # entries-in-buffer/entries-written: 3/3 #P:8
> #
> # _-----=> irqs-off
> # / _----=> need-resched
> # | / _---=> hardirq/softirq
> # || / _--=> preempt-depth
> # ||| / delay
> # TASK-PID CPU# |||| TIMESTAMP FUNCTION
> # | | | |||| | |
> blockdev-185 [002] ...1 72.604266: p_blkdev_put_0: (blkdev_put+0x0/0x130)
> blockdev-185 [002] ...1 72.604276: p___blkdev_put_0: (__blkdev_put+0x0/0x220)
> blockdev-185 [002] d..2 72.604288: r___blkdev_put_0: (blkdev_put+0x50/0x130 <- __blkdev_put)
>
> So the __blkdev_put() is called once from blkdev_put().
> Next, we do same trace with accessing */dev/sda1* (a partition).
>
> root@...note2:/sys/kernel/debug/tracing# echo > trace
> root@...note2:/sys/kernel/debug/tracing# echo 1 > events/kprobes/enable
I can't find 'events/kprobes' in my VM with upstream kernel, also not found
the dir under fedora31(5.5.15-200) & rhel8(v4.18 based).
Could you share me how to enable the kprobes event? I guess some kernel
config options are required.
> root@...note2:/sys/kernel/debug/tracing# blockdev --getbsz /dev/sda1
> 4096
> root@...note2:/sys/kernel/debug/tracing# echo 0 > events/kprobes/enable
I used samples/kprobes/kprobe_example.c by replacing __do_fork with
__blkdev_put for confirming this issue, and only one __blkdev_put trace is
observed in dmesg log when running 'blockdev --getbsz /dev/sda1'.
Thanks,
Ming
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