Re: [PATCH V7 5/7] cpufreq: Register notifiers with the PM QoS framework

[Dmitry Osipenko]

15.10.2019 14:46, Viresh Kumar ÐÐÑÐÑ:
> On 22-09-19, 23:12, Dmitry Osipenko wrote:
>> Hello Viresh,
>>
>> This patch causes use-after-free on a cpufreq driver module reload. Please take a look, thanks in advance.
>>
>>
>> [   87.952369] ==================================================================
>> [   87.953259] BUG: KASAN: use-after-free in notifier_chain_register+0x4f/0x9c
>> [   87.954031] Read of size 4 at addr e6abbd0c by task modprobe/243
>>
>> [   87.954901] CPU: 1 PID: 243 Comm: modprobe Tainted: G        W
>> 5.3.0-next-20190920-00185-gf61698eab956-dirty #2408
>> [   87.956077] Hardware name: NVIDIA Tegra SoC (Flattened Device Tree)
>> [   87.956807] [<c0110aad>] (unwind_backtrace) from [<c010bb71>] (show_stack+0x11/0x14)
>> [   87.957709] [<c010bb71>] (show_stack) from [<c0d37b25>] (dump_stack+0x89/0x98)
>> [   87.958616] [<c0d37b25>] (dump_stack) from [<c02937e1>]
>> (print_address_description.constprop.0+0x3d/0x340)
>> [   87.959785] [<c02937e1>] (print_address_description.constprop.0) from [<c0293c6b>]
>> (__kasan_report+0xe3/0x12c)
>> [   87.960907] [<c0293c6b>] (__kasan_report) from [<c014988f>] (notifier_chain_register+0x4f/0x9c)
>> [   87.962001] [<c014988f>] (notifier_chain_register) from [<c01499b5>]
>> (blocking_notifier_chain_register+0x29/0x3c)
>> [   87.963180] [<c01499b5>] (blocking_notifier_chain_register) from [<c06f7ee9>]
>> (dev_pm_qos_add_notifier+0x79/0xf8)
>> [   87.964339] [<c06f7ee9>] (dev_pm_qos_add_notifier) from [<c092927d>] (cpufreq_online+0x5e1/0x8a4)
>> [   87.965351] [<c092927d>] (cpufreq_online) from [<c09295c9>] (cpufreq_add_dev+0x79/0x80)
>> [   87.966247] [<c09295c9>] (cpufreq_add_dev) from [<c06eb9d3>] (subsys_interface_register+0xc3/0x100)
>> [   87.967297] [<c06eb9d3>] (subsys_interface_register) from [<c0926e53>]
>> (cpufreq_register_driver+0x13b/0x1ec)
>> [   87.968476] [<c0926e53>] (cpufreq_register_driver) from [<bf800435>]
>> (tegra20_cpufreq_probe+0x165/0x1a8 [tegra20_cpufreq])
> 
> Hi Dmitry,
> 
> Thanks for the bug report and I was finally able to reproduce it at my end and
> this was quite an interesting debugging exercise :)
> 
> When a cpufreq driver gets registered, we register with the subsys interface and
> it calls cpufreq_add_dev() for each CPU, starting from CPU0. And so the QoS
> notifiers get added to the first CPU of the policy, i.e. CPU0 in common cases.
> 
> When the cpufreq driver gets unregistered, we unregister with the subsys
> interface and it calls cpufreq_remove_dev() for each CPU, starting from CPU0
> (should have been in reverse order I feel). We remove the QoS notifier only when
> cpufreq_remove_dev() gets called for the last CPU of the policy, lets call it
> CPUx. Now this has a different notifier list as compared to CPU0.
> 
> In short, we are adding the cpufreq notifiers to CPU0 and removing them from
> CPUx. When we try to add it again by inserting the module for second time, we
> find a node in the notifier list which is already freed but still in the list as
> we removed it from CPUx's list (which doesn't do anything as the node wasn't
> there in the first place).
> 
> @Rafael: How do you see we solve this problem ? Here are the options I could
> think of:
> 
> - Update subsys layer to reverse the order of devices while unregistering (this
>   will fix the current problem, but we will still have corner cases hanging
>   around, like if the CPU0 is hotplugged out, etc).
> 
> - Update QoS framework with the knowledge of related CPUs, this has been pending
>   until now from my side. And this is the thing we really need to do. Eventually
>   we shall have only a single notifier list for all CPUs of a policy, at least
>   for MIN/MAX frequencies.
> 
> - ??
> 

Viresh, thank you very much! Looking forward to a fix :)