linux-kernel - [PATCHv3 07/50] arm: Wire up dump_backtrace

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Date:   Sat, 18 Apr 2020 21:19:01 +0100
From:   Dmitry Safonov <dima@...sta.com>
To:     linux-kernel@...r.kernel.org
Cc:     Dmitry Safonov <0x7f454c46@...il.com>,
        Dmitry Safonov <dima@...sta.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>, Jiri Slaby <jslaby@...e.com>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Russell King <linux@...linux.org.uk>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        clang-built-linux@...glegroups.com
Subject: [PATCHv3 07/50] arm: Wire up dump_backtrace_{entry,stm}

Currently, the log-level of show_stack() depends on a platform
realization. It creates situations where the headers are printed with
lower log level or higher than the stacktrace (depending on
a platform or user).

Furthermore, it forces the logic decision from user to an architecture
side. In result, some users as sysrq/kdb/etc are doing tricks with
temporary rising console_loglevel while printing their messages.
And in result it not only may print unwanted messages from other CPUs,
but also omit printing at all in the unlucky case where the printk()
was deferred.

Introducing log-level parameter and KERN_UNSUPPRESSED [1] seems
an easier approach than introducing more printk buffers.
Also, it will consolidate printings with headers.

Now that c_backtrace() always emits correct loglvl, use it for printing.

Cc: Russell King <linux@...linux.org.uk>
Cc: Will Deacon <will@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org
Cc: clang-built-linux@...glegroups.com
[1]: https://lore.kernel.org/lkml/20190528002412.1625-1-dima@arista.com/T/#u
Signed-off-by: Dmitry Safonov <dima@...sta.com>
---
 arch/arm/kernel/traps.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 0f09ace18e6c..e1be6c85327c 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -68,13 +68,15 @@ void dump_backtrace_entry(unsigned long where, unsigned long from,
 	unsigned long end = frame + 4 + sizeof(struct pt_regs);
 
 #ifdef CONFIG_KALLSYMS
-	printk("[<%08lx>] (%ps) from [<%08lx>] (%pS)\n", where, (void *)where, from, (void *)from);
+	printk("%s[<%08lx>] (%ps) from [<%08lx>] (%pS)\n",
+		loglvl, where, (void *)where, from, (void *)from);
 #else
-	printk("Function entered at [<%08lx>] from [<%08lx>]\n", where, from);
+	printk("%sFunction entered at [<%08lx>] from [<%08lx>]\n",
+		loglvl, where, from);
 #endif
 
 	if (in_entry_text(from) && end <= ALIGN(frame, THREAD_SIZE))
-		dump_mem("", "Exception stack", frame + 4, end);
+		dump_mem(loglvl, "Exception stack", frame + 4, end);
 }
 
 void dump_backtrace_stm(u32 *stack, u32 instruction, const char *loglvl)
@@ -89,12 +91,12 @@ void dump_backtrace_stm(u32 *stack, u32 instruction, const char *loglvl)
 			if (++x == 6) {
 				x = 0;
 				p = str;
-				printk("%s\n", str);
+				printk("%s%s\n", loglvl, str);
 			}
 		}
 	}
 	if (p != str)
-		printk("%s\n", str);
+		printk("%s%s\n", loglvl, str);
 }
 
 #ifndef CONFIG_ARM_UNWIND
-- 
2.26.0