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SubjectRe: [PATCH] tty: hvc: don't allocate a buffer for console print on stack
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> You shouldn't use 'static' data either, that's not always guaranteed to
> be DMA-able, right?

I naively thought all 'static' data was linked into .data and the
section was always kmapped.

> What about allocating it dynamically? That's the correct thing to do.

Yep, the solution was more welcomed and happened earlier:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c4baad50297d84bde1a7ad45e50c73adae4a2192

On 03/17/2017 08:09 AM, Greg Kroah-Hartman wrote:
> On Fri, Feb 17, 2017 at 11:42:45PM +0300, Jan Dakinevich wrote:
>> The buffer is used by virtio console driver as DMA buffer. Since v4.9
>> (if VMAP_STACK is enabled) we shouldn't use the stack for DMA.
>
> You shouldn't use 'static' data either, that's not always guaranteed to
> be DMA-able, right?
>
>>
>> Signed-off-by: Jan Dakinevich <jan.dakinevich@gmail.com>
>> ---
>> drivers/tty/hvc/hvc_console.c | 7 ++++++-
>> 1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
>> index 9b5c0fb..1ce6aaf 100644
>> --- a/drivers/tty/hvc/hvc_console.c
>> +++ b/drivers/tty/hvc/hvc_console.c
>> @@ -143,10 +143,15 @@ static struct hvc_struct *hvc_get_by_index(int index)
>> static void hvc_console_print(struct console *co, const char *b,
>> unsigned count)
>> {
>> - char c[N_OUTBUF] __ALIGNED__;
>> unsigned i = 0, n = 0;
>> int r, donecr = 0, index = co->index;
>>
>> + /*
>> + * Access to the buffer is serialized by console_sem in caller code from
>> + * kernel/printk/printk.c
>> + */
>> + static char c[N_OUTBUF] __ALIGNED__;
>
> What about allocating it dynamically? That's the correct thing to do.
>
> thanks,
>
> greg k-h
>

--
Best regards
Jan Dakinevich

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