Re: [PATCH v2 1/5] printk/nmi: Generic solution for safe printk in NMI
From: Petr Mladek <pmladek@suse.com>
Date: 2015-12-04 15:29:31
Also in:
linux-arm-kernel, linux-mips, linux-sh, lkml, sparclinux
On Wed 2015-12-02 13:45:16, Michael Ellerman wrote:
On Fri, 2015-11-27 at 12:09 +0100, Petr Mladek wrote:quoted
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")....quoted
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 @@...quoted
+ +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