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SubjectRe: [PATCH] kprobes: bugfix: checks kprobes_all_disarmed in unoptimized_kprobe().
On 2015/1/19 20:45, Masami Hiramatsu wrote:
> (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@localhost ~]# cd /sys/kernel/debug/tracing/
> [root@localhost tracing]# echo p do_fork+5 > kprobe_events # setup new event
> [root@localhost tracing]# echo $$ > set_ftrace_pid # trace only this process
> [root@localhost tracing]# echo 1 > events/kprobes/p_do_fork_5/enable # enable it
> [root@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@localhost tracing]# cat ../kprobes/list
> ffffffff810bc1c5 k do_fork+0x5 [OPTIMIZED] # and it is actually optimized
> [root@localhost tracing]# echo 0 > ../kprobes/enabled # disable *ALL* kprobes
> [root@localhost tracing]# echo > trace # clear events
> [root@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@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,
>

Thanks to your quick reply. I'll post an improved v1 patch tomorrow.




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