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SubjectRe: [PATCH] powerpc: kernel/kgdb.c: fix memory leakage
On 02/08/2013 10:41 AM, Benjamin Herrenschmidt wrote:
> On Thu, 2013-01-31 at 20:04 -0600, Jason Wessel wrote:
>
>>> diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
>>> index 8747447..5ca82cd 100644
>>> --- a/arch/powerpc/kernel/kgdb.c
>>> +++ b/arch/powerpc/kernel/kgdb.c
>>> @@ -154,12 +154,12 @@ static int kgdb_handle_breakpoint(struct pt_regs *regs)
>>> static int kgdb_singlestep(struct pt_regs *regs)
>>> {
>>> struct thread_info *thread_info, *exception_thread_info;
>>> - struct thread_info *backup_current_thread_info = \
>>> - (struct thread_info *)kmalloc(sizeof(struct thread_info), GFP_KERNEL);
>>> + struct thread_info *backup_current_thread_info;
>>
>>
>>
>> Woh... This is definitely wrong. You have found a problem for sure,
>> but this is not the right way to fix it.
>>
>> It is not a good idea to kmalloc while single stepping because you can
>> hang the kernel if you single step any operation in kmalloc().
>
> Ok. I applied the fix because it was obviously correct vs. the previous
> version of the code (ie. the kmalloc was already there)
>
>> I am in the process of going through all the kgdb mails from the last
>> few months while I had been away from the project, so I didn't catch
>> this one and I see it has upstream commit (fefd9e6f8). I'll submit
>> another patch to fix this the right way and use a static variable.
>> This is ok to use a static variable here because this is not something
>> we can recursively call at a single CPU level.
>
> But a static will be shared by all CPUs or do you mean a per-cpu one ?
>
>> If Ben prefers we not burn the memory unless kgdb is active we can
>> kmalloc / kfree the space we need at the time that kgdb is
>> initialized. Else we can go with this patch you see below. We'll see
>> what Ben desires.
>
> What about the stack ? thread info isn't very big...


Actually booke already copy the thread_info when we enter the debug exception,
and I will send a patch to do the same thing for book3e, so I also remove these
copying action here then we're happy without these nasty stuff :)

Tiejun

>
> Cheers,
> Ben.
>
>> -----
>> diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
>> index a7bc752..bb12c8b 100644
>> --- a/arch/powerpc/kernel/kgdb.c
>> +++ b/arch/powerpc/kernel/kgdb.c
>> @@ -151,15 +151,16 @@ static int kgdb_handle_breakpoint(struct pt_regs *regs)
>> return 1;
>> }
>>
>> +static struct thread_info kgdb_backup_thread_info[NR_CPUS];
>> +
>> static int kgdb_singlestep(struct pt_regs *regs)
>> {
>> struct thread_info *thread_info, *exception_thread_info;
>> - struct thread_info *backup_current_thread_info;
>> + int cpu = raw_smp_processor_id();
>>
>> if (user_mode(regs))
>> return 0;
>>
>> - backup_current_thread_info = (struct thread_info *)kmalloc(sizeof(struct thread_info), GFP_KERNEL);
>> /*
>> * On Book E and perhaps other processors, singlestep is handled on
>> * the critical exception stack. This causes current_thread_info()
>> @@ -175,7 +176,7 @@ static int kgdb_singlestep(struct pt_regs *regs)
>>
>> if (thread_info != exception_thread_info) {
>> /* Save the original current_thread_info. */
>> - memcpy(backup_current_thread_info, exception_thread_info, sizeof *thread_info);
>> + memcpy(&kgdb_backup_thread_info[cpu], exception_thread_info, sizeof *thread_info);
>> memcpy(exception_thread_info, thread_info, sizeof *thread_info);
>> }
>>
>> @@ -183,9 +184,8 @@ static int kgdb_singlestep(struct pt_regs *regs)
>>
>> if (thread_info != exception_thread_info)
>> /* Restore current_thread_info lastly. */
>> - memcpy(exception_thread_info, backup_current_thread_info, sizeof *thread_info);
>> + memcpy(exception_thread_info, &kgdb_backup_thread_info[cpu], sizeof *thread_info);
>>
>> - kfree(backup_current_thread_info);
>> return 1;
>> }
>>
>>
>> -----
>>
>>
>> Thanks,
>> Jason.
>>
>>
>>>
>>> if (user_mode(regs))
>>> return 0;
>>>
>>> + backup_current_thread_info = (struct thread_info *)kmalloc(sizeof(struct thread_info), GFP_KERNEL);
>>> /*
>>> * On Book E and perhaps other processors, singlestep is handled on
>>> * the critical exception stack. This causes current_thread_info()
>>> @@ -185,6 +185,7 @@ static int kgdb_singlestep(struct pt_regs *regs)
>>> /* Restore current_thread_info lastly. */
>>> memcpy(exception_thread_info, backup_current_thread_info, sizeof *thread_info);
>>>
>>> + kfree(backup_current_thread_info);
>>> return 1;
>>> }
>>>
>>>
>
>
>
>



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