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From:   Ming Lei <tom.leiming@gmail.com>
Date:   Wed, 17 Jun 2020 18:30:39 +0800
Message-ID: <CACVXFVO5saamQXs0naLamTKJfXZMW+p446weeqJK=9+V34UM0g@mail.gmail.com>
Subject: krobe: __blkdev_put probe is missed
To:     "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Masami Hiramatsu <mhiramat@kernel.org>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        linux-block <linux-block@vger.kernel.org>
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Sender: linux-kernel-owner@vger.kernel.org
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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