[PATCH] kprobes: bugfix: checks kprobes_all_disarmed in unoptimized_kprobe().
Masami Hiramatsu
masami.hiramatsu.pt at hitachi.com
Mon Jan 19 04:45:34 PST 2015
(2015/01/19 20:21), Wang Nan wrote:
> On 2015/1/19 17:05, Masami Hiramatsu wrote:
>> Hi Wang,
>>
>> I've found a problem on this patch, since kprobes calls unoptioize_kprobe
>> with kprobes_all_disarmed=true when trying to disable all kprobes, this
>> cause a serious problem.
>>
>> Moreover, I couldn't reproduce your reported bug on my 3.19-rc4 kernel.
>> Could you test it again?
>>
>
> I tested it again based on 3.19-rc5 and found that the problem still exists.
> My testing is based on QEMU.
>
> First I tested my kprobeopt for ARM, then on x86_64. The test results are pasted
> at the bottom of this mail. Commands after 'gdb attaches to QEMU' is my actions
> on a gdb console attached to QEMU; commands after 'inside virtual machine' is
> what I do in Linux run under QEMU.
Thank you for the reporting.
So, now I know what happened, the problem is "debugfs/kprobes/enabled doesn't work
correctly on optimized kprobes". Please make update the patch description.
I also reproduced the bug without gdb.
Here is the log.
----
[root at localhost ~]# cd /sys/kernel/debug/tracing/
[root at localhost tracing]# echo p do_fork+5 > kprobe_events # setup new event
[root at localhost tracing]# echo $$ > set_ftrace_pid # trace only this process
[root at localhost tracing]# echo 1 > events/kprobes/p_do_fork_5/enable # enable it
[root at localhost tracing]# cat trace # check the trace data
# 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
# | | | |||| | |
bash-3883 [006] d... 279.799023: p_do_fork_5: (do_fork+0x5/0x360) # OK, now tracing
[root at localhost tracing]# cat ../kprobes/list
ffffffff810bc1c5 k do_fork+0x5 [OPTIMIZED] # and it is actually optimized
[root at localhost tracing]# echo 0 > ../kprobes/enabled # disable *ALL* kprobes
[root at localhost tracing]# echo > trace # clear events
[root at localhost tracing]# cat trace # this should show empty buffer
# 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
# | | | |||| | |
bash-3883 [006] d... 337.770785: p_do_fork_5: (do_fork+0x5/0x360) # But still tracing!
[root at localhost tracing]# cat trace # Check again
# tracer: nop
#
# entries-in-buffer/entries-written: 2/2 #P:8
#
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
bash-3883 [006] d... 337.770785: p_do_fork_5: (do_fork+0x5/0x360)
bash-3883 [006] d... 345.592178: p_do_fork_5: (do_fork+0x5/0x360) # We are tracing!!
So, after global disabling kprobes, ALL kprobes event should be disabled, but not.
OK, I think your first patch is better than the second one, but not enough.
What we should do is use kprobes_all_disarmed for force option like below.
unoptimize_kprobe(p, kprobes_all_disarmed); /* Try to unoptimize */
We also would better to check the flag in unregistering path for skipping unneeded
disarming process when kprobes globally disarmed.
Thank you,
--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt at hitachi.com
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