linux-kernel - Re: [PATCH] kdb: use correct pointer when 'btc' calls 'btt'

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Date:   Wed, 26 Sep 2018 13:19:18 +0200
From:   Christophe LEROY <christophe.leroy@....fr>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     Jason Wessel <jason.wessel@...driver.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        kgdb-bugreport@...ts.sourceforge.net, stable@...r.kernel.org,
        me@...in.cc
Subject: Re: [PATCH] kdb: use correct pointer when 'btc' calls 'btt'



Le 26/09/2018 à 13:11, Daniel Thompson a écrit :
> On 16/09/2018 20:06, Daniel Thompson wrote:
>> On Fri, Sep 14, 2018 at 12:35:44PM +0000, Christophe Leroy wrote:
>>> On a powerpc 8xx, 'btc' fails as follows:
>>>
>>> Entering kdb (current=0x(ptrval), pid 282) due to Keyboard Entry
>>> kdb> btc
>>> btc: cpu status: Currently on cpu 0
>>> Available cpus: 0
>>> kdb_getarea: Bad address 0x0
>>>
>>> when booting the kernel with 'debug_boot_weak_hash', it fails as well
>>>
>>> Entering kdb (current=0xba99ad80, pid 284) due to Keyboard Entry
>>> kdb> btc
>>> btc: cpu status: Currently on cpu 0
>>> Available cpus: 0
>>> kdb_getarea: Bad address 0xba99ad80
>>>
>>> On other platforms, Oopses have been observed too, see
>>> https://github.com/linuxppc/linux/issues/139
>>>
>>> This is due to btc calling 'btt' with %p pointer as an argument.
>>>
>>> This patch replaces %p by %px to get the real pointer value as
>>> expected by 'btt'
>>>
>>> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
>>> Cc: <stable@...r.kernel.org> # 4.15+
>>
>> Would a Fixes: be better here?
>> Fixes: ad67b74d2469d9b82 ("printk: hash addresses printed with %p")
> 
> Christophe, When you add the Fixes: could you also add my
> 
> Reviewed-by: Daniel Thompson <daniel.thompson@...aro.org>


Ok, thanks for the review, but do I have to do anything really ?

The Fixes: and now your Reviewed-by: appear automatically in patchwork 
(https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=65715), 
so I believe they'll be automatically included when Jason or someone 
else takes the patch, no ?

Christophe

> 
> 
> Thanks.
> 
> 
>>
>> No blame attached to Tobin, but the fixes makes it super clear what
>> changed and why this breaks kdb (which was not explicitly called out
>> the patch description).
>>
>>
>> Daniel.
>>
>>> ---
>>>   kernel/debug/kdb/kdb_bt.c | 4 ++--
>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/kernel/debug/kdb/kdb_bt.c b/kernel/debug/kdb/kdb_bt.c
>>> index 6ad4a9fcbd6f..7921ae4fca8d 100644
>>> --- a/kernel/debug/kdb/kdb_bt.c
>>> +++ b/kernel/debug/kdb/kdb_bt.c
>>> @@ -179,14 +179,14 @@ kdb_bt(int argc, const char **argv)
>>>                   kdb_printf("no process for cpu %ld\n", cpu);
>>>                   return 0;
>>>               }
>>> -            sprintf(buf, "btt 0x%p\n", KDB_TSK(cpu));
>>> +            sprintf(buf, "btt 0x%px\n", KDB_TSK(cpu));
>>>               kdb_parse(buf);
>>>               return 0;
>>>           }
>>>           kdb_printf("btc: cpu status: ");
>>>           kdb_parse("cpu\n");
>>>           for_each_online_cpu(cpu) {
>>> -            sprintf(buf, "btt 0x%p\n", KDB_TSK(cpu));
>>> +            sprintf(buf, "btt 0x%px\n", KDB_TSK(cpu));
>>>               kdb_parse(buf);
>>>               touch_nmi_watchdog();
>>>           }
>>> -- 
>>> 2.13.3
>>>