BKL: That's all, folks

This removes the implementation of the big kernel lock,
at last. A lot of people have worked on this in the
past, I so the credit for this patch should be with
everyone who participated in the hunt.

The names on the Cc list are the people that were the
most active in this, according to the recorded git
history, in alphabetical order.

Signed-off-by: Arnd Bergmann <[email protected]>
Acked-by: Alan Cox <[email protected]>
Cc: Alessio Igor Bogani <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Andrew Hendry <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Eric W. Biederman <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Hans Verkuil <[email protected]>
Acked-by: Ingo Molnar <[email protected]>
Cc: Jan Blunck <[email protected]>
Cc: John Kacur <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Oliver Neukum <[email protected]>
Cc: Paul Menage <[email protected]>
Acked-by: Thomas Gleixner <[email protected]>
Cc: Trond Myklebust <[email protected]>

include/linux/hardirq.h

@@ -93,13 +93,6 @@
  */
 #define in_nmi()	(preempt_count() & NMI_MASK)
 
-#if defined(CONFIG_PREEMPT) && defined(CONFIG_BKL)
-# include <linux/sched.h>
-# define PREEMPT_INATOMIC_BASE (current->lock_depth >= 0)
-#else
-# define PREEMPT_INATOMIC_BASE 0
-#endif
-
 #if defined(CONFIG_PREEMPT)
 # define PREEMPT_CHECK_OFFSET 1
 #else
@@ -113,7 +106,7 @@
  * used in the general case to determine whether sleeping is possible.
  * Do not use in_atomic() in driver code.
  */
-#define in_atomic()	((preempt_count() & ~PREEMPT_ACTIVE) != PREEMPT_INATOMIC_BASE)
+#define in_atomic()	((preempt_count() & ~PREEMPT_ACTIVE) != 0)
 
 /*
  * Check whether we were atomic before we did preempt_disable():

init/Kconfig

@@ -69,11 +69,6 @@ config BROKEN_ON_SMP
 	depends on BROKEN || !SMP
 	default y
 
-config LOCK_KERNEL
-	bool
-	depends on (SMP || PREEMPT) && BKL
-	default y
-
 config INIT_ENV_ARG_LIMIT
 	int
 	default 32 if !UML

kernel/sched.c

@@ -32,7 +32,6 @@
 #include <linux/init.h>
 #include <linux/uaccess.h>
 #include <linux/highmem.h>
-#include <linux/smp_lock.h>
 #include <asm/mmu_context.h>
 #include <linux/interrupt.h>
 #include <linux/capability.h>
@@ -3945,9 +3944,6 @@ asmlinkage void __sched schedule(void)
 	rcu_note_context_switch(cpu);
 	prev = rq->curr;
 
-	release_kernel_lock(prev);
-need_resched_nonpreemptible:
-
 	schedule_debug(prev);
 
 	if (sched_feat(HRTICK))
@@ -4010,9 +4006,6 @@ asmlinkage void __sched schedule(void)
 
 	post_schedule(rq);
 
-	if (unlikely(reacquire_kernel_lock(prev)))
-		goto need_resched_nonpreemptible;
-
 	preempt_enable_no_resched();
 	if (need_resched())
 		goto need_resched;
@@ -8074,7 +8067,7 @@ static inline int preempt_count_equals(int preempt_offset)
 {
 	int nested = (preempt_count() & ~PREEMPT_ACTIVE) + rcu_preempt_depth();
 
-	return (nested == PREEMPT_INATOMIC_BASE + preempt_offset);
+	return (nested == preempt_offset);
 }
 
 void __might_sleep(const char *file, int line, int preempt_offset)

lib/Kconfig.debug

@@ -470,15 +470,6 @@ config DEBUG_MUTEXES
 	 This feature allows mutex semantics violations to be detected and
 	 reported.
 
-config BKL
-	bool "Big Kernel Lock" if (SMP || PREEMPT)
-	default y
-	help
-	  This is the traditional lock that is used in old code instead
-	  of proper locking. All drivers that use the BKL should depend
-	  on this symbol.
-	  Say Y here unless you are working on removing the BKL.
-
 config DEBUG_LOCK_ALLOC
 	bool "Lock debugging: detect incorrect freeing of live locks"
 	depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT

lib/Makefile

@@ -43,7 +43,6 @@ obj-$(CONFIG_GENERIC_FIND_LAST_BIT) += find_last_bit.o
 CFLAGS_hweight.o = $(subst $(quote),,$(CONFIG_ARCH_HWEIGHT_CFLAGS))
 obj-$(CONFIG_GENERIC_HWEIGHT) += hweight.o
 
-obj-$(CONFIG_LOCK_KERNEL) += kernel_lock.o
 obj-$(CONFIG_BTREE) += btree.o
 obj-$(CONFIG_DEBUG_PREEMPT) += smp_processor_id.o
 obj-$(CONFIG_DEBUG_LIST) += list_debug.o