On 2022/9/1 22:18, Petr Mladek wrote:
> On Thu 2022-09-01 10:27:06, Zhen Lei wrote:
>> The patch->mod is not a protected object of mutex_lock(&klp_mutex). Since
>> it's in the error handling branch, it might not be helpful to reduce lock
>> conflicts, but it can reduce some code size.
>>
>> Before:
>> text data bss dec hex filename
>> 10330 464 8 10802 2a32 kernel/livepatch/core.o
>>
>> After:
>> text data bss dec hex filename
>> 10307 464 8 10779 2a1b kernel/livepatch/core.o
>
> Please, is this part of some longterm effort to reduce the size of
> the kernel? Or is this just some random observation?
>
>
>> Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
>> ---
>> kernel/livepatch/core.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
>> index 42f7e716d56bf72..cb7abc821a50584 100644
>> --- a/kernel/livepatch/core.c
>> +++ b/kernel/livepatch/core.c
>> @@ -1041,9 +1041,9 @@ int klp_enable_patch(struct klp_patch *patch)
>> mutex_lock(&klp_mutex);
>>
>> if (!klp_is_patch_compatible(patch)) {
>> + mutex_unlock(&klp_mutex);
>> pr_err("Livepatch patch (%s) is not compatible with the already installed livepatches.\n",
>> patch->mod->name);
>> - mutex_unlock(&klp_mutex);
>
> I do not see how this change could reliably reduce the code size.
>
> As Joe wrote, it looks like a random effect that is specific to a
> particular compiler version, compilation options, and architecture.
>
> I am against these kind of random microptimizations. It is just a call
> for problems. If you move printk() outside of a lock, you need to make
> sure that the information is not racy.
OK.
mutex_lock(&klp_mutex);
if (!klp_is_patch_compatible(patch)) {
mutex_unlock(&klp_mutex);
<--------- Do you mean the incompatible patches maybe disabled at this point?
pr_err("Livepatch patch (%s) ...\n", patch->mod->name);
return -EINVAL;
}
>
> It might be safe in this particular case. But it is a bad practice.
> It adds an extra work. It is error-prone with questionable gain.
>
> I am sorry but I NACK this patch. There must be better ways to
OK
> reduce the kernel binary size.
>
> Best Regards,
> Petr
> .
>
--
Regards,
Zhen Lei
