Re: [PATCH RFC] BKL not necessary in cpuid_open
From: Sven-Thorsten Dietrich <hidden>
Date: 2009-10-07 19:14:49
Also in:
lkml
Subsystem:
library code, the rest · Maintainers:
Andrew Morton, Linus Torvalds
On Wed, 2009-10-07 at 20:19 +0200, John Kacur wrote:
I've been staring at the BKL lock in cpuid_open, and I can't see what it is protecting. However, I may have missed something - even something obvious, so comments are welcome.
I have been using this patch to first see if the BKL is being used simply as mutex, which would allow easier break-down. Sven Subject: Introduce the BKL-MUTEX, to allow proving the code that From: Sven-Thorsten Dietrich sdietrich@suse.de Sat Oct 3 01:26:01 2009 -0700 Date: Sat Oct 3 01:26:01 2009 -0700: Git: 4bfea26de550100d193c49278d657485e792dfe5 just needs a global kernel mutex, without all the funky preemption bits... Acked-by: Sven-Thorsten Dietrich <redacted>
diff --git a/include/linux/smp_mutex.h b/include/linux/smp_mutex.h
new file mode 100644
index 0000000..6c45a96
--- /dev/null
+++ b/include/linux/smp_mutex.h@@ -0,0 +1,22 @@ +#ifndef __LINUX_SMPMUTEX_H +#define __LINUX_SMPMUTEX_H + +#ifdef CONFIG_LOCK_KERNEL + +extern void lock_kernel_mutex(void); +extern void unlock_kernel_mutex(void); + +static inline void cycle_kernel_mutex(void) +{ + lock_kernel_mutex(); + unlock_kernel_mutex(); +} + +#else + +#define lock_kernel_mutex() do { } while(0) +#define unlock_kernel_mutex() do { } while(0) +#define cycle_kernel_mutex() do { } while(0) + +#endif /* CONFIG_LOCK_KERNEL */ +#endif /* __LINUX_SMPMUTEX_H */
diff --git a/lib/Makefile b/lib/Makefile
index 2e78277..c71ffdc 100644
--- a/lib/Makefile
+++ b/lib/Makefile@@ -40,7 +40,7 @@ lib-$(CONFIG_GENERIC_FIND_FIRST_BIT) += find_next_bit.o lib-$(CONFIG_GENERIC_FIND_NEXT_BIT) += find_next_bit.o obj-$(CONFIG_GENERIC_FIND_LAST_BIT) += find_last_bit.o obj-$(CONFIG_GENERIC_HWEIGHT) += hweight.o -obj-$(CONFIG_LOCK_KERNEL) += kernel_lock.o +obj-$(CONFIG_LOCK_KERNEL) += kernel_lock.o kernel_mutex.o obj-$(CONFIG_DEBUG_PREEMPT) += smp_processor_id.o obj-$(CONFIG_DEBUG_LIST) += list_debug.o obj-$(CONFIG_DEBUG_OBJECTS) += debugobjects.o
diff --git a/lib/kernel_mutex.c b/lib/kernel_mutex.c
new file mode 100644
index 0000000..1d587a8
--- /dev/null
+++ b/lib/kernel_mutex.c@@ -0,0 +1,37 @@ +/* + * lib/kernel_mutex.c + * + * This is the preemptible BKL - To be used transitionally to + * prove those subsystems still using lock_kernel, but really + * requiring a global mutex. + */ +#include <linux/smp_mutex.h> +#include <linux/module.h> +#include <linux/kallsyms.h> +#include <linux/semaphore.h> +#include <linux/mutex.h> + +/* + * The 'big kernel mutex' + * + * Don't use in new code. + */ +static __cacheline_aligned_in_smp DEFINE_MUTEX(kernel_mutex); + + +/* + * Getting the kernel mutex. + */ +void __lockfunc lock_kernel_mutex(void) +{ + mutex_lock(&kernel_mutex); +} + +void __lockfunc unlock_kernel_mutex(void) +{ + mutex_unlock(&kernel_mutex); +} + +EXPORT_SYMBOL(lock_kernel_mutex); +EXPORT_SYMBOL(unlock_kernel_mutex); +