Re: [PATCH] blk-mq: avoid sysfs buffer overflow by too many CPU cores

[Hannes Reinecke <hare@suse.de>]

On 11/4/19 2:56 AM, Jens Axboe wrote:
> On 11/3/19 4:57 PM, Ming Lei wrote:
>> On Sun, Nov 3, 2019 at 8:28 AM Chaitanya Kulkarni
>> <Chaitanya.Kulkarni@wdc.com> wrote:
>>>
>>> Ming,
>>>
>>> On 11/02/2019 01:02 AM, Ming Lei wrote:
>>>> It is reported that sysfs buffer overflow can be triggered in case
>>>> of too many CPU cores(>841 on 4K PAGE_SIZE) when showing CPUs of
>>>> hctx via/sys/block/$DEV/mq/$N/cpu_list.
>>>>
>>>> So use snprintf for avoiding the potential buffer overflow.
>>>>
>>>> This version doesn't change the attribute format, and simply stop
>>>> to show CPU number if the buffer is to be overflow.
>>>
>>> Does it make sense to also add a print or WARN_ON in case of overflow ?
>>
>> Yes, it does, could you cook a patch for that?
> 
> No it doesn't. The WARN_ON brings absolutely nothing. If you're using
> a script, it gets the same values out and doesn't see the warning. If
> it's a human cat'ing it, they will probably already realize that
> we're missing CPUs. Or maybe not even see the warning. It's useless.
> 
> We should either make this seqfile, or just kill the file. Those are
> the only two options that make any sense.
> 
I'd rather retain that file; it proved really useful when debugging
interrupt affinity issues.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      Teamlead Storage & Networking
hare@suse.de			                  +49 911 74053 688
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