From: Masami Hiramatsu <mhiramat@kernel.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Ming Lei <ming.lei@redhat.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Ming Lei <tom.leiming@gmail.com>,
"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>,
linux-block <linux-block@vger.kernel.org>
Subject: Re: kprobe: __blkdev_put probe is missed
Date: Tue, 23 Jun 2020 08:47:06 +0900 [thread overview]
Message-ID: <20200623084706.e6e99e99d7da6690e7a6c199@kernel.org> (raw)
In-Reply-To: <20200622090148.6e0f2ac9@oasis.local.home>
On Mon, 22 Jun 2020 09:01:48 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:
> On Mon, 22 Jun 2020 08:27:53 +0800
> Ming Lei <ming.lei@redhat.com> wrote:
>
> > Can you kprobe guys improve the implementation for covering this case?
> > For example, put probe on 3) in case the above situation is recognized.
>
> To do so would require solving the halting problem.
>
> https://en.wikipedia.org/wiki/Halting_problem
>
> Or perhaps reading the DWARF output of the compiler to determine if it
> optimized the location you are looking for.
As far as I can see, gcc-9.3 doesn't generate this information :(
Maybe the optimizer forgot to push the tail-call callsite information
to dwarf generator when making a recursive tail-call to a loop.
> The first case is impossible to solve, the second would take a lot of
> work, (are you going to fund it?)
What I can provide is "--skip-prologue" option for the perf-probe
which will be similar to the "-P" option. If the compiler correctly
generates the information, we can enable it automatically. But
as far as I can see, it doesn't.
[OT] DWARF has its option(and GNU extension) but it seems not correctly
implemented yet.
http://www.dwarfstd.org/ShowIssue.php?issue=100909.2
What I found on __blkdev_put and the callers, the "tail-call to other
function" were recorded as a call-site DIE with DW_AT_tail_call. But
if the "tail-call to itself (recursive call)" was expanded as a loop,
it was just disappeared. No call-site information, nor the DW_AT_tail_call.
Thank you,
--
Masami Hiramatsu <mhiramat@kernel.org>
next prev parent reply other threads:[~2020-06-22 23:47 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-17 10:30 krobe: __blkdev_put probe is missed Ming Lei
2020-06-18 12:54 ` kprobe: " Ming Lei
2020-06-18 13:56 ` Masami Hiramatsu
2020-06-18 23:19 ` Ming Lei
2020-06-19 5:12 ` Masami Hiramatsu
2020-06-19 7:28 ` Ming Lei
2020-06-19 12:19 ` Steven Rostedt
2020-06-19 13:32 ` Ming Lei
2020-06-19 15:35 ` Masami Hiramatsu
2020-06-19 23:28 ` Ming Lei
2020-06-20 0:59 ` Steven Rostedt
2020-06-20 1:37 ` Masami Hiramatsu
2020-06-22 0:27 ` Ming Lei
2020-06-22 1:34 ` Masami Hiramatsu
2020-06-22 13:01 ` Steven Rostedt
2020-06-22 23:47 ` Masami Hiramatsu [this message]
2020-06-23 0:38 ` Masami Hiramatsu
2020-06-23 5:28 ` Masami Hiramatsu
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