From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752365AbcFEKWK (ORCPT ); Sun, 5 Jun 2016 06:22:10 -0400 Received: from wtarreau.pck.nerim.net ([62.212.114.60]:21776 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752128AbcFEKWA (ORCPT ); Sun, 5 Jun 2016 06:22:00 -0400 From: Willy Tarreau To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: "Steven Rostedt (Red Hat)" , stable@vger.kernel.org#v3.5+, Willy Tarreau Subject: [PATCH 3.10 046/143] tracing: Fix trace_printk() to print when not using bprintk() Date: Sun, 5 Jun 2016 12:19:09 +0200 Message-Id: <1465122046-9645-47-git-send-email-w@1wt.eu> X-Mailer: git-send-email 2.8.0.rc2.1.gbe9624a In-Reply-To: <1465122046-9645-1-git-send-email-w@1wt.eu> References: <1465122046-9645-1-git-send-email-w@1wt.eu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Steven Rostedt (Red Hat)" commit 3debb0a9ddb16526de8b456491b7db60114f7b5e upstream. The trace_printk() code will allocate extra buffers if the compile detects that a trace_printk() is used. To do this, the format of the trace_printk() is saved to the __trace_printk_fmt section, and if that section is bigger than zero, the buffers are allocated (along with a message that this has happened). If trace_printk() uses a format that is not a constant, and thus something not guaranteed to be around when the print happens, the compiler optimizes the fmt out, as it is not used, and the __trace_printk_fmt section is not filled. This means the kernel will not allocate the special buffers needed for the trace_printk() and the trace_printk() will not write anything to the tracing buffer. Adding a "__used" to the variable in the __trace_printk_fmt section will keep it around, even though it is set to NULL. This will keep the string from being printed in the debugfs/tracing/printk_formats section as it is not needed. Reported-by: Vlastimil Babka Fixes: 07d777fe8c398 "tracing: Add percpu buffers for trace_printk()" Cc: stable@vger.kernel.org # v3.5+ Signed-off-by: Steven Rostedt Signed-off-by: Willy Tarreau --- include/linux/kernel.h | 6 +++--- kernel/trace/trace_printk.c | 3 +++ 2 files changed, 6 insertions(+), 3 deletions(-) diff --git a/include/linux/kernel.h b/include/linux/kernel.h index 341551c..5f4554b 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -557,7 +557,7 @@ do { \ #define do_trace_printk(fmt, args...) \ do { \ - static const char *trace_printk_fmt \ + static const char *trace_printk_fmt __used \ __attribute__((section("__trace_printk_fmt"))) = \ __builtin_constant_p(fmt) ? fmt : NULL; \ \ @@ -604,7 +604,7 @@ extern int __trace_puts(unsigned long ip, const char *str, int size); */ #define trace_puts(str) ({ \ - static const char *trace_printk_fmt \ + static const char *trace_printk_fmt __used \ __attribute__((section("__trace_printk_fmt"))) = \ __builtin_constant_p(str) ? str : NULL; \ \ @@ -624,7 +624,7 @@ extern void trace_dump_stack(int skip); #define ftrace_vprintk(fmt, vargs) \ do { \ if (__builtin_constant_p(fmt)) { \ - static const char *trace_printk_fmt \ + static const char *trace_printk_fmt __used \ __attribute__((section("__trace_printk_fmt"))) = \ __builtin_constant_p(fmt) ? fmt : NULL; \ \ diff --git a/kernel/trace/trace_printk.c b/kernel/trace/trace_printk.c index a9077c1..fdb23e8 100644 --- a/kernel/trace/trace_printk.c +++ b/kernel/trace/trace_printk.c @@ -272,6 +272,9 @@ static int t_show(struct seq_file *m, void *v) const char *str = *fmt; int i; + if (!*fmt) + return 0; + seq_printf(m, "0x%lx : \"", *(unsigned long *)fmt); /* -- 2.8.0.rc2.1.gbe9624a