On Wed 2015-12-02 13:45:16, Michael Ellerman wrote:
> On Fri, 2015-11-27 at 12:09 +0100, Petr Mladek wrote:
>
> > printk() takes some locks and could not be used a safe way in NMI
> > context.
> >
> > The chance of a deadlock is real especially when printing
> > stacks from all CPUs. This particular problem has been addressed
> > on x86 by the commit a9edc8809328 ("x86/nmi: Perform a safe NMI stack
> > trace on all CPUs").
>
> ...
>
> > diff --git a/kernel/printk/nmi.c b/kernel/printk/nmi.c
> > new file mode 100644
> > index 000000000000..3989e13a0021
> > --- /dev/null
> > +++ b/kernel/printk/nmi.c
> > @@ -0,0 +1,200 @@
>
> ...
>
> > +
> > +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) -
> > + sizeof(struct irq_work)];
> > +};
> > +static DEFINE_PER_CPU(struct nmi_seq_buf, nmi_print_seq);
>
>
> PAGE_SIZE isn't always 4K.
>
> On typical powerpc systems this will give you 128K, and on some 512K, which is
> probably not what we wanted.
Good point!
> The existing code just did:
>
> #define NMI_BUF_SIZE 4096
I will change this to 8192. The 4kB were not enough in some cases.
Best Regards,
Petr
