Messages in this thread | | | Subject | Re: [PATCH v2 1/5] printk/nmi: Generic solution for safe printk in NMI | From | Michael Ellerman <> | Date | Wed, 02 Dec 2015 13:45:16 +1100 |
| |
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.
The existing code just did:
#define NMI_BUF_SIZE 4096
So I think you should just go back to doing that.
cheers
| |