* [PATCH] tty: hvc: don't allocate a buffer for console print on stack
@ 2017-02-17 20:42 Jan Dakinevich
2017-03-17 5:09 ` Greg Kroah-Hartman
0 siblings, 1 reply; 3+ messages in thread
From: Jan Dakinevich @ 2017-02-17 20:42 UTC (permalink / raw)
To: Greg Kroah-Hartman, Jiri Slaby, Jan Dakinevich, Peter Hurley,
Dan Carpenter, Arnd Bergmann, Amit Shah, virtualization,
linuxppc-dev, linux-kernel
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.
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__;
+
/* Console access attempt outside of acceptable console range. */
if (index >= MAX_NR_HVC_CONSOLES)
return;
--
1.9.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] tty: hvc: don't allocate a buffer for console print on stack
2017-02-17 20:42 [PATCH] tty: hvc: don't allocate a buffer for console print on stack Jan Dakinevich
@ 2017-03-17 5:09 ` Greg Kroah-Hartman
2017-03-20 15:55 ` Jan Dakinevich
0 siblings, 1 reply; 3+ messages in thread
From: Greg Kroah-Hartman @ 2017-03-17 5:09 UTC (permalink / raw)
To: Jan Dakinevich
Cc: Jiri Slaby, Peter Hurley, Dan Carpenter, Arnd Bergmann,
Amit Shah, virtualization, linuxppc-dev, linux-kernel
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
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] tty: hvc: don't allocate a buffer for console print on stack
2017-03-17 5:09 ` Greg Kroah-Hartman
@ 2017-03-20 15:55 ` Jan Dakinevich
0 siblings, 0 replies; 3+ messages in thread
From: Jan Dakinevich @ 2017-03-20 15:55 UTC (permalink / raw)
To: Greg Kroah-Hartman
Cc: Jiri Slaby, Peter Hurley, Dan Carpenter, Arnd Bergmann,
Amit Shah, virtualization, linuxppc-dev, linux-kernel
> 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
^ permalink raw reply [flat|nested] 3+ messages in thread
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2017-03-17 5:09 ` Greg Kroah-Hartman
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