linux-kernel - Re: [PATCH v2 0/3] printk: introduce new macros pr_<level>

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Date:   Wed, 30 Nov 2022 18:57:09 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Thomas Weißschuh <linux@...ssschuh.net>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        linux-pm@...r.kernel.org, Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Andy Whitcroft <apw@...onical.com>,
        Joe Perches <joe@...ches.com>, linux-kernel@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        Dwaipayan Ray <dwaipayanray1@...il.com>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>
Subject: Re: [PATCH v2 0/3] printk: introduce new macros pr_<level>_cont()

On Fri, Nov 25, 2022 at 8:10 PM Thomas Weißschuh <linux@...ssschuh.net> wrote:
>
> This series adds new printk wrapper macros pr_<level>_cont().
> These create continuation messages with an explicit level.
>
> Explicit levels are useful when a continuation message is split from its main
> message. Without the explicit level KERN_DEFAULT ("warn" by default) is used
> which can lead to stray partial log messages when filtering by level.
>
> Also checkpatch is modified to recommend the new macros over plain pr_cont().
>
> Lastly the new macros are used in kernel/power/process.c as this file uses
> continuation messages during system suspend-resume which creates a high
> likelyhood of interspersed messages.

Well, if process.c is the only problematic piece of code in this
respect, I'm not sure if adding the new infrastructure for its benefit
alone is worth it, because it can very well do without pr_cont() at
all.

Please see the patch below (compiled only, sorry for gmail-induced
white space damage).  I'll submit it properly later if it works for
everyone.

---
 kernel/power/process.c |   25 ++++++++++---------------
 1 file changed, 10 insertions(+), 15 deletions(-)

Index: linux-pm/kernel/power/process.c
===================================================================
--- linux-pm.orig/kernel/power/process.c
+++ linux-pm/kernel/power/process.c
@@ -27,6 +27,8 @@ unsigned int __read_mostly freeze_timeou

 static int try_to_freeze_tasks(bool user_only)
 {
+    const char *what = user_only ? "user space processes" :
+                    "remaining freezable tasks";
     struct task_struct *g, *p;
     unsigned long end_time;
     unsigned int todo;
@@ -36,6 +38,8 @@ static int try_to_freeze_tasks(bool user
     bool wakeup = false;
     int sleep_usecs = USEC_PER_MSEC;

+    pr_info("Freezing %s\n", what);
+
     start = ktime_get_boottime();

     end_time = jiffies + msecs_to_jiffies(freeze_timeout_msecs);
@@ -82,9 +86,8 @@ static int try_to_freeze_tasks(bool user
     elapsed_msecs = ktime_to_ms(elapsed);

     if (todo) {
-        pr_cont("\n");
-        pr_err("Freezing of tasks %s after %d.%03d seconds "
-               "(%d tasks refusing to freeze, wq_busy=%d):\n",
+        pr_err("Freezing %s %s after %d.%03d seconds "
+               "(%d tasks refusing to freeze, wq_busy=%d):\n", what,
                wakeup ? "aborted" : "failed",
                elapsed_msecs / 1000, elapsed_msecs % 1000,
                todo - wq_busy, wq_busy);
@@ -101,8 +104,8 @@ static int try_to_freeze_tasks(bool user
             read_unlock(&tasklist_lock);
         }
     } else {
-        pr_cont("(elapsed %d.%03d seconds) ", elapsed_msecs / 1000,
-            elapsed_msecs % 1000);
+        pr_info("Freezing %s completed (elapsed %d.%03d seconds)\n",
+            what, elapsed_msecs / 1000, elapsed_msecs % 1000);
     }

     return todo ? -EBUSY : 0;
@@ -130,14 +133,11 @@ int freeze_processes(void)
         static_branch_inc(&freezer_active);

     pm_wakeup_clear(0);
-    pr_info("Freezing user space processes ... ");
     pm_freezing = true;
     error = try_to_freeze_tasks(true);
-    if (!error) {
+    if (!error)
         __usermodehelper_set_disable_depth(UMH_DISABLED);
-        pr_cont("done.");
-    }
-    pr_cont("\n");
+
     BUG_ON(in_atomic());

     /*
@@ -166,14 +166,9 @@ int freeze_kernel_threads(void)
 {
     int error;

-    pr_info("Freezing remaining freezable tasks ... ");
-
     pm_nosig_freezing = true;
     error = try_to_freeze_tasks(false);
-    if (!error)
-        pr_cont("done.");

-    pr_cont("\n");
     BUG_ON(in_atomic());

     if (error)