Re: [PATCH 2/2] virtio-console: remove unnecessary kmemdup()

[Xianting Tian <xianting.tian@linux.alibaba.com>]

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在 2021/8/2 下午3:25, Jiri Slaby 写道:
> Hi,
>
> why is this 2/2? I seem (Lore neither) to find 1/2.
You didn't receive 1/2?
[PATCH 1/2] tty: hvc: pass DMA capable memory to put_chars()
https://lkml.org/lkml/2021/8/1/8 <https://lkml.org/lkml/2021/8/1/8>
>
> On 01. 08. 21, 7:16, Xianting Tian wrote:
>> hvc framework will never pass stack memory to the put_chars() function,
>
> Am I blind or missing something?
>
> hvc_console_print(...)
> {
>   char c[N_OUTBUF]
> ...
>   cons_ops[index]->put_chars(vtermnos[index], c, i);
>
> The same here:
>
> hvc_poll_put_char(..., char ch)
> {
> ...
>    n = hp->ops->put_chars(hp->vtermno, &ch, 1);
>
> AFAICS both of them *pass* a pointer to stack variable.

yes, I discussed the issue with Arnd before in below thread,  you can 
get the history, thanks

https://lkml.org/lkml/2021/7/27/494 <https://lkml.org/lkml/2021/7/27/494>

>
>> So the calling of kmemdup() is unnecessary, remove it.
>>
>> Fixes: c4baad5029 ("virtio-console: avoid DMA from stack")
>
> This patch doesn't "Fix" -- it reverts the commit. You should've CCed 
> the author too.

yes, we discussed ther issue in above thread, which we CCed the author.

>
>> Signed-off-by: Xianting Tian <xianting.tian@linux.alibaba.com>
>> ---
>>   drivers/char/virtio_console.c | 12 ++----------
>>   1 file changed, 2 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/char/virtio_console.c 
>> b/drivers/char/virtio_console.c
>> index 7eaf303a7..4ed3ffb1d 100644
>> --- a/drivers/char/virtio_console.c
>> +++ b/drivers/char/virtio_console.c
>> @@ -1117,8 +1117,6 @@ static int put_chars(u32 vtermno, const char 
>> *buf, int count)
>>   {
>>       struct port *port;
>>       struct scatterlist sg[1];
>> -    void *data;
>> -    int ret;
>>         if (unlikely(early_put_chars))
>>           return early_put_chars(vtermno, buf, count);
>> @@ -1127,14 +1125,8 @@ static int put_chars(u32 vtermno, const char 
>> *buf, int count)
>>       if (!port)
>>           return -EPIPE;
>>   -    data = kmemdup(buf, count, GFP_ATOMIC);
>> -    if (!data)
>> -        return -ENOMEM;
>> -
>> -    sg_init_one(sg, data, count);
>> -    ret = __send_to_port(port, sg, 1, count, data, false);
>> -    kfree(data);
>> -    return ret;
>> +    sg_init_one(sg, buf, count);
>> +    return __send_to_port(port, sg, 1, count, (void *)buf, false);
>>   }
>>     /*
>>
>
>

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