linux-kernel - Re: Floating point exception by perf record

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Message-ID: <20100405183127.GA3677@ghostprotocols.net>
Date:	Mon, 5 Apr 2010 15:31:27 -0300
From:	Arnaldo Carvalho de Melo <acme@...radead.org>
To:	Hitoshi Mitake <mitake@....info.waseda.ac.jp>
Cc:	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Floating point exception by perf record

Em Sun, Apr 04, 2010 at 05:10:57PM +0900, Hitoshi Mitake escreveu:
> I suffered a mysterious floating point exception when executing perf
> on current tip/master.
>
> For example,
>
> % sudo ./perf lock record ./perf bench sched messaging
> # Running sched/messaging benchmark...
> # 20 sender and receiver processes per group
> # 10 groups == 400 processes run
>
>      Total time: 1.375 [sec]
> [ perf record: Woken up 0 times to write data ]
> [ perf record: Captured and wrote 160.002 MB perf.data (~6990599 samples) ]
> [1]    26348 floating point exception  sudo ./perf lock record ./perf  
> bench sched messaging
>
> dmesg says that
>
> [10212.752490] perf[26348] trap divide error ip:7fade8564310  
> sp:7fff46d926e8 error:0 in libnewt.so.0.52.2[7fade8556000+15000]
>
> Example is of perf lock, but this is not a special phenomenon of perf lock,
> other users of perf record, like perf sched, caused the same problem.
>
> I found that this might be caused by the line 283 of perf.c
>
> 	if (fclose(stdout)) # <- closing stdout!
> 		die("close failed on standard output: %s", strerror(errno));
>
> I don't know well about libnewt, do you know something like cause?
>
> The version of libnewt I'm using is 0.52.2 (default of Debian lenny)

I just built a kernel where 'perf lock' can work, but I'm seeing a
different problem:

[root@...pio ~]# perf lock trace | head -3
  Warning: Error: expected 'data' but read 'overwrite'
         swapper-0     [000]   619.086424: lock_acquire: 0xffff8800029d4b28 &q->lock
         swapper-0     [000]   619.086429: lock_acquire: 0xffff8800029d08f8 &ctx->lock
         swapper-0     [000]   619.086439: lock_acquire: 0xffffffff81a38e58 clockevents_lock
[root@...pio ~]# perf lock report | head -3
  Warning: Error: expected 'data' but read 'overwrite'
                ID                 Name   acquired  contended total wait (ns)   max wait (ns)   min wait (ns) 

0xffff8800029d4b28             &q->lock          0          0               0               0               0 
[root@...pio ~]# 

My system details:

[root@...pio ~]# uname -a
Linux doppio.ghostprotocols.net 2.6.34-rc3-tip+ #1 SMP Mon Apr 5 13:49:42 BRT 2010 x86_64 x86_64 x86_64 GNU/Linux
[root@...pio ~]# rpm -q newt
newt-0.52.10-4.fc11.x86_64
[root@...pio ~]# 

No segfaults here :-\

- Arnaldo
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