On Thu 2015-05-14 11:35:01, Wang Long wrote: > From: "Steven Rostedt (Red Hat)" <rostedt@xxxxxxxxxxx> > > commit afdc34a3d3b823a12a93b822ee1efb566f884032 upstream. > > Being able to divert printk to call another function besides the normal > logging is useful for such things like NMI handling. If some functions > are to be called from NMI that does printk() it is possible to lock up > the box if the nmi handler triggers when another printk is happening. > > One example of this use is to perform a stack trace on all CPUs via NMI. > But if the NMI is to do the printk() it can cause the system to lock up. > By allowing the printk to be diverted to another function that can safely > record the printk output and then print it when it in a safe context > then NMIs will be safe to call these functions like show_regs(). > > Link: http://lkml.kernel.org/p/20140619213952.209176403@xxxxxxxxxxx > > Tested-by: Jiri Kosina <jkosina@xxxxxxx> > Acked-by: Jiri Kosina <jkosina@xxxxxxx> > Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> > Reviewed-by: Petr Mladek <pmladek@xxxxxxx> > [wanglong: backport to 3.10 stable > - adjust context > ] > Signed-off-by: Wang Long <long.wanglong@xxxxxxxxxx> > Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx> > --- > include/linux/percpu.h | 3 +++ > include/linux/printk.h | 2 ++ > kernel/printk.c | 38 +++++++++++++++++++++++++++++--------- > 3 files changed, 34 insertions(+), 9 deletions(-) > > diff --git a/include/linux/percpu.h b/include/linux/percpu.h > index cc88172..bb1d29c 100644 > --- a/include/linux/percpu.h > +++ b/include/linux/percpu.h > @@ -755,4 +755,7 @@ do { \ > __pcpu_double_call_return_bool(__this_cpu_cmpxchg_double_, (pcp1), (pcp2), (oval1), (oval2), (nval1), (nval2)) > #endif > > +/* To avoid include hell, as printk can not declare this, we declare it here */ > +DECLARE_PER_CPU(printk_func_t, printk_func); > + > #endif /* __LINUX_PERCPU_H */ > diff --git a/include/linux/printk.h b/include/linux/printk.h > index 708b8a8..ebc7f3e 100644 > --- a/include/linux/printk.h > +++ b/include/linux/printk.h > @@ -144,6 +144,8 @@ extern int kptr_restrict; > > extern void wake_up_klogd(void); > > +typedef int(*printk_func_t)(const char *fmt, va_list args); > + > void log_buf_kexec_setup(void); > void __init setup_log_buf(int early); > void dump_stack_set_arch_desc(const char *fmt, ...); > diff --git a/kernel/printk.c b/kernel/printk.c > index fd0154a..d3d929d 100644 > --- a/kernel/printk.c > +++ b/kernel/printk.c > @@ -1657,6 +1657,30 @@ asmlinkage int printk_emit(int facility, int level, > } > EXPORT_SYMBOL(printk_emit); > > +int vprintk_default(const char *fmt, va_list args) > +{ > + int r; > + > +#ifdef CONFIG_KGDB_KDB > + if (unlikely(kdb_trap_printk)) { > + r = vkdb_printf(fmt, args); > + return r; > + } > +#endif > + r = vprintk_emit(0, -1, NULL, 0, fmt, args); > + > + return r; There is broken indentation in this hunk. The rest of the patch looks fine. Best Regards, Petr -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html