linux-kernel - Re: [PATCH 2/6] tracing: increase size of number of possible events

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Date:	Sun, 26 Apr 2009 14:53:24 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 2/6] tracing: increase size of number of possible events

Steven Rostedt wrote:
> On Fri, 24 Apr 2009, Steven Rostedt wrote:
> 
>> On Fri, 24 Apr 2009, Li Zefan wrote:
>>> console 1:
>>>  # cat /debug/tracing/trace_pipe
>>>
>>> console 2:
>>> while (1) {
>>> 	insmod trace-events-sample.ko
>>> 	echo foo_bar > /debug/tracing/set_event
>>> 	rmmod trace-events-sample.ko
>>> }
>>>
>>> I got this immediately:
>>>
>>> BUG: unable to handle kernel NULL pointer dereference at 0000006f
>>> IP: [<c05210f3>] bstr_printf+0x2ce/0x302
>>> ...
>>> Call Trace:
>>>  [<c0476d12>] ? trace_seq_bprintf+0x28/0x41
>>>  [<c0477569>] ? trace_bprint_print+0x58/0x6c
>>>  [<c0472ffc>] ? print_trace_line+0x2c5/0x2df
>>>  [<c0428a41>] ? sub_preempt_count+0x85/0xa0
>>>  [<c04758cf>] ? tracing_read_pipe+0x118/0x191
>>>  [<c04757b7>] ? tracing_read_pipe+0x0/0x191
>>>  [<c04b09f9>] ? vfs_read+0x8f/0x136
>>>  [<c04b0da3>] ? sys_read+0x40/0x65
>>>  [<c0402a68>] ? sysenter_do_call+0x12/0x36
>>>
>>> (We can even get other crashes..)
>>>
>> Can you send me your full bootlog and config. I'm not able to reproduce 
>> this.
> 
> And the SHA1 of the HEAD of the git repo you are using.
> 
> Thanks,
> 

the HEAD: 9ce5424d75e56891905b77d1589924765e62059a + this patch

(I commented out "hi" from the sample module)

I think it's because "type" is wrapped back to 0. I changed the test script
like this:

while (foo_bar.id < 65536)
{
	insmod trace-events-sample.ko
	rmmod trace-events-sample.ko
}

for ((; ;))
{
        insmod /home/lizf/linux-2.6-tip/samples/trace_events/*.ko
        echo trace-events-sample:foo_bar > /mnt/tracing/set_event
        sleep 1
        cat /mnt/tracing/trace
        rmmod /home/lizf/linux-2.6-tip/samples/trace_events/*.ko
}

See what I saw:

# tracer: nop
#
#           TASK-PID    CPU#    TIMESTAMP  FUNCTION
#              | |       |          |         |
           <...>-8449  [000]  1305.284303: Unknown type 0
           <...>-8449  [000]  1305.376875: Unknown type 0
           <...>-8457  [000]  1306.384178:  <-
           <...>-8457  [000]  1306.476297:  <-
           <...>-8467  [000]  1307.501050:  1819043176:111:R ==> [-1478325281] 1819017216:  0:R <...>
           <...>-8467  [000]  1307.589070:  1819043176:111:R ==> [-1629971735] 1819017216:  1:R <...>
           <...>-8476  [000]  1308.611875:  1819043176:111:R   + [-1444866625] 1819017216:  0:R <...>
           <...>-8476  [000]  1308.700941:  1819043176:111:R   + [1819017216] 1819017216:  1:R <...>
           <...>-8485  [001]  1309.710751:
 <=
 <=
 <= 0
 <=
 <=
 <=
 <=
           <...>-8485  [001]  1309.807031:
 <=
 <=
 <=
 <=
 <=
 <=
 <=
           <...>-8493  [001]  1310.815615: : o./test.sh: line 15:  8505 Killed                  cat /mnt/tracing/trace
(OOPS!!)

.config and full log are attached

(ps: I will be on vacation, and won't be able to reply to any mail in the
 following one week..)

View attachment "dmesg.log" of type "text/x-log" (28995 bytes)

View attachment "myconfig" of type "text/plain" (64135 bytes)