linux-kernel - Re: [PATCHv3 12/50] csky: Add show_stack

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Message-Id: <20200515122340.d0d93b7a29846934e161ef41@linux-foundation.org>
Date:   Fri, 15 May 2020 12:23:40 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Dmitry Safonov <dima@...sta.com>
Cc:     linux-kernel@...r.kernel.org,
        Dmitry Safonov <0x7f454c46@...il.com>,
        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>,
        Guo Ren <guoren@...nel.org>
Subject: Re: [PATCHv3 12/50] csky: Add show_stack_loglvl()

On Sat, 18 Apr 2020 21:19:06 +0100 Dmitry Safonov <dima@...sta.com> wrote:

> 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.
> 
> Introduce show_stack_loglvl(), that eventually will substitute
> show_stack().

The csky code has changed a lot in linux-next due to 18c07d23da5a
("csky: Fixup calltrace panic").  I redid this patch as below.  Can we
please review and test?


From: Dmitry Safonov <dima@...sta.com>
Subject: csky: add show_stack_loglvl()

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.

Introduce show_stack_loglvl(), that eventually will substitute
show_stack().

[1]: https://lore.kernel.org/lkml/20190528002412.1625-1-dima@arista.com/T/#u

Link: http://lkml.kernel.org/r/20200418201944.482088-13-dima@arista.com
Signed-off-by: Dmitry Safonov <dima@...sta.com>
Cc: Guo Ren <guoren@...nel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 arch/csky/kernel/stacktrace.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

--- a/arch/csky/kernel/stacktrace.c~csky-add-show_stack_loglvl
+++ a/arch/csky/kernel/stacktrace.c
@@ -91,14 +91,21 @@ static void notrace walk_stackframe(stru
 
 static bool print_trace_address(unsigned long pc, void *arg)
 {
-	print_ip_sym(pc);
+	print_ip_sym((const char *)arg, pc);
 	return false;
 }
 
+void show_stack_loglvl(struct task_struct *task, unsigned long *sp,
+		       const char *loglvl)
+{
+	pr_cont("Call Trace:\n");
+	walk_stackframe(task, NULL, print_trace_address, (void *)loglvl);
+}
+
 void show_stack(struct task_struct *task, unsigned long *sp)
 {
 	pr_cont("Call Trace:\n");
-	walk_stackframe(task, NULL, print_trace_address, NULL);
+	walk_stackframe(task, NULL, print_trace_address, KERN_INFO);
 }
 
 static bool save_wchan(unsigned long pc, void *arg)
_