Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753907AbbERNxi (ORCPT ); Mon, 18 May 2015 09:53:38 -0400 Received: from cantor2.suse.de ([195.135.220.15]:45842 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753903AbbERNx1 (ORCPT ); Mon, 18 May 2015 09:53:27 -0400 Date: Mon, 18 May 2015 15:56:03 +0200 From: Petr Mladek To: Wang Long Cc: rostedt@goodmis.org, jkosina@suse.cz, gregkh@linuxfoundation.org, stable@vger.kernel.org, wanglong@laoqinren.net, peifeiyue@huawei.com, linux-kernel@vger.kernel.org, morgan.wang@huawei.com, paulmck@linux.vnet.ibm.com, dzickus@redhat.com, x86@kernel.org, sasha.levin@oracle.com Subject: Re: [RFC PATCH 14/17] printk: Add per_cpu printk func to allow printk to be diverted Message-ID: <20150518135603.GD2632@pathway.suse.cz> References: <1431603304-162571-1-git-send-email-long.wanglong@huawei.com> <1431603304-162571-15-git-send-email-long.wanglong@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1431603304-162571-15-git-send-email-long.wanglong@huawei.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3312 Lines: 91 On Thu 2015-05-14 11:35:01, Wang Long wrote: > From: "Steven Rostedt (Red Hat)" > > 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@goodmis.org > > Tested-by: Jiri Kosina > Acked-by: Jiri Kosina > Acked-by: Paul E. McKenney > Reviewed-by: Petr Mladek > [wanglong: backport to 3.10 stable > - adjust context > ] > Signed-off-by: Wang Long > Signed-off-by: Steven Rostedt > --- > 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 linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/