linux-kernel - [RFC][PATCHv5 04/13] printk: add enforce

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Message-Id: <20170815025625.1977-5-sergey.senozhatsky@gmail.com>
Date:   Tue, 15 Aug 2017 11:56:16 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Jan Kara <jack@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Eric Biederman <ebiederm@...ssion.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, Pavel Machek <pavel@....cz>,
        Andreas Mohr <andi@...as.de>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: [RFC][PATCHv5 04/13] printk: add enforce_emergency parameter

This param permits user-space to forcibly on/off printk emergency
mode via `/sys/module/printk/parameters/enforce_emergency' node.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 7 +++++++
 kernel/printk/printk.c                          | 8 +++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index b5b6d5d24596..001f578ec5f5 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3215,6 +3215,13 @@
 
 			default: off.
 
+	printk.enforce_emergency=
+			This parameter allows to disable/enable printing
+			offloading to printk kthread.
+			Format: <bool> (1 - emergency, 0 - permit offloading).
+
+			default: off.
+
 	processor.max_cstate=	[HW,ACPI]
 			Limit processor to maximum C-state
 			max_cstate=9 overrides any DMI blacklist limit.
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 5d4b4beeebf5..3a0e78812818 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -455,9 +455,15 @@ static cpumask_var_t printk_offload_cpus;
 static atomic_t printk_emergency __read_mostly;
 /*
  * Disable printk_kthread permanently. Unlike `oops_in_progress'
- * it doesn't go back to 0.
+ * it doesn't go back to 0 (unless set by user-space).
  */
 static bool printk_enforce_emergency __read_mostly;
+
+module_param_named(enforce_emergency, printk_enforce_emergency,
+		    bool, 0644);
+MODULE_PARM_DESC(printk_enforce_emergency,
+		 "don't offload message printing to printk kthread");
+
 /*
  * The number of seconds a task can print before it offloads printing
  * duty to printk_kthread. 0 indicates 'no limit'.
-- 
2.14.1