> On Nov 27, 2015, at 19:09, Petr Mladek <pmladek@xxxxxxxx> wrote:
>
> Testing has shown that the backtrace sometimes does not fit
> into the 4kB temporary buffer that is used in NMI context.
>
> The warnings are gone when I double the temporary buffer size.
>
> Note that this problem existed even in the x86-specific
> implementation that was added by the commit a9edc8809328
> ("x86/nmi: Perform a safe NMI stack trace on all CPUs").
> Nobody noticed it because it did not print any warnings.
>
> Signed-off-by: Petr Mladek <pmladek@xxxxxxxx>
> ---
> kernel/printk/nmi.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/printk/nmi.c b/kernel/printk/nmi.c
> index 8af1e4016719..6111644d5f01 100644
> --- a/kernel/printk/nmi.c
> +++ b/kernel/printk/nmi.c
> @@ -42,7 +42,7 @@ atomic_t nmi_message_lost;
> struct nmi_seq_buf {
> atomic_t len; /* length of written data */
> struct irq_work work; /* IRQ work that flushes the buffer */
> - unsigned char buffer[PAGE_SIZE - sizeof(atomic_t) -
> + unsigned char buffer[2 * PAGE_SIZE - sizeof(atomic_t) -
> sizeof(struct irq_work)];
> };
>
why not define like this:
union {
struct {atomic_t len;
struct irq_work work;
}
unsigned char buffer[PAGE_SIZE * 2] ;
}
we can make sure the union is 2 PAGE_SIZE .
Thanks
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