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

[Jens Axboe <axboe@kernel.dk>]

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.

-- 
Jens Axboe