linux-kernel - [PATCH v2 1/3] kdb: Remove unused kdb

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Date:   Tue, 29 Nov 2016 10:37:54 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Jason Wessel <jason.wessel@...driver.com>
Cc:     Daniel Thompson <daniel.thompson@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        linux-kernel@...r.kernel.org, Petr Mladek <pmladek@...e.com>
Subject: [PATCH v2 1/3] kdb: Remove unused kdb_event handling

kdb_event state variable is only set but never checked in
the kernel code.

http://www.spinics.net/lists/kdb/msg01733.html suggests that
this variable affected WARN_CONSOLE_UNLOCKED() in the original
implementation. But this check never went upstream.

The semantic is unclear and racy. The value is updated after
the kdb_printf_lock is acquired and after it is released.
It should be symmetric at minimum. The value should be manipulated
either inside or outside the locked area.

Fortunately, it seems that the original function is gone and
we could simply remove the state variable.

Suggested-by: Daniel Thompson <daniel.thompson@...aro.org>
Signed-off-by: Petr Mladek <pmladek@...e.com>
---
 include/linux/kdb.h         | 1 -
 kernel/debug/kdb/kdb_io.c   | 2 --
 kernel/debug/kdb/kdb_main.c | 1 -
 3 files changed, 4 deletions(-)

diff --git a/include/linux/kdb.h b/include/linux/kdb.h
index 410decacff8f..eb706188dc23 100644
--- a/include/linux/kdb.h
+++ b/include/linux/kdb.h
@@ -77,7 +77,6 @@
  * number whenever the kernel debugger is entered.
  */
 extern int kdb_initial_cpu;
-extern atomic_t kdb_event;
 
 /* Types and messages used for dynamically added kdb shell commands */
 
diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index fc1ef736253c..3faadc988ec0 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -576,7 +576,6 @@ int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap)
 		KDB_STATE_SET(PRINTF_LOCK);
 		spin_lock_irqsave(&kdb_printf_lock, flags);
 		got_printf_lock = 1;
-		atomic_inc(&kdb_event);
 	} else {
 		__acquire(kdb_printf_lock);
 	}
@@ -851,7 +850,6 @@ int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap)
 		got_printf_lock = 0;
 		spin_unlock_irqrestore(&kdb_printf_lock, flags);
 		KDB_STATE_CLEAR(PRINTF_LOCK);
-		atomic_dec(&kdb_event);
 	} else {
 		__release(kdb_printf_lock);
 	}
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 2a20c0dfdafc..ca183919d302 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -60,7 +60,6 @@
  * Kernel debugger state flags
  */
 int kdb_flags;
-atomic_t kdb_event;
 
 /*
  * kdb_lock protects updates to kdb_initial_cpu.  Used to
-- 
1.8.5.6