From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steven Rostedt Date: Thu, 27 Apr 2017 16:14:58 +0000 Subject: Re: [PATCH v5 1/4] printk/nmi: generic solution for safe printk in NMI Message-Id: <20170427121458.2be577cc@gandalf.local.home> List-Id: References: <1461239325-22779-1-git-send-email-pmladek@suse.com> <1461239325-22779-2-git-send-email-pmladek@suse.com> <20170419131341.76bc7634@gandalf.local.home> <20170420033112.GB542@jagdpanzerIV.localdomain> <20170420131154.GL3452@pathway.suse.cz> In-Reply-To: <20170420131154.GL3452@pathway.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-arm-kernel@lists.infradead.org On Thu, 20 Apr 2017 15:11:54 +0200 Petr Mladek wrote: > > >From c530d9dee91c74db5e6a198479e2e63b24cb84a2 Mon Sep 17 00:00:00 2001 > From: Petr Mladek > Date: Thu, 20 Apr 2017 10:52:31 +0200 > Subject: [PATCH] printk: Use the main logbuf in NMI when logbuf_lock is > available I tried this patch. It's better because I get the end of the trace, but I do lose the beginning of it: ** 196358 printk messages dropped ** [ 102.321182] perf-5981 0.... 12983650us : d_path <-seq_path The way I tested it was by adding this: Index: linux-trace.git/kernel/trace/trace_functions.c =================================--- linux-trace.git.orig/kernel/trace/trace_functions.c +++ linux-trace.git/kernel/trace/trace_functions.c @@ -469,8 +469,11 @@ ftrace_cpudump_probe(unsigned long ip, u struct trace_array *tr, struct ftrace_probe_ops *ops, void *data) { - if (update_count(ops, ip, data)) - ftrace_dump(DUMP_ORIG); + char *killer = NULL; + + panic_on_oops = 1; /* force panic */ + wmb(); + *killer = 1; } static int Then doing the following: # echo 1 > /proc/sys/kernel/ftrace_dump_on_oops # trace-cmd start -p function # echo nmi_handle:cpudump > /debug/tracing/set_ftrace_filter # perf record -c 100 -a sleep 1 And that triggers the crash. -- Steve