by Arnd Bergmann

[permalink] [raw]

Subject: [PATCH v2] 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]>
---

This is the version I'm adding to linux-next once
the all the other patches have made it in there
through the maintainer trees.

Changes from previous version:
* Remove CONFIG_BKL Kconfig symbol
* Fix remaining user of PREEMPT_INATOMIC_BASE

include/linux/hardirq.h | 9 +---
include/linux/smp_lock.h | 65 ----------------------
init/Kconfig | 5 --
kernel/sched.c | 9 +---
lib/Kconfig.debug | 9 ---
lib/Makefile | 1 -
lib/kernel_lock.c | 136 ----------------------------------------------
7 files changed, 2 insertions(+), 232 deletions(-)
delete mode 100644 include/linux/smp_lock.h
delete mode 100644 lib/kernel_lock.c

diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index 32f9fd6..ba36217 100644
--- a/include/linux/hardirq.h
+++ b/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():
diff --git a/include/linux/smp_lock.h b/include/linux/smp_lock.h
deleted file mode 100644
index 3a19882..0000000
--- a/include/linux/smp_lock.h
+++ /dev/null
@@ -1,65 +0,0 @@
-#ifndef __LINUX_SMPLOCK_H
-#define __LINUX_SMPLOCK_H
-
-#ifdef CONFIG_LOCK_KERNEL
-#include <linux/sched.h>
-
-extern int __lockfunc __reacquire_kernel_lock(void);
-extern void __lockfunc __release_kernel_lock(void);
-
-/*
- * Release/re-acquire global kernel lock for the scheduler
- */
-#define release_kernel_lock(tsk) do { \
- if (unlikely((tsk)->lock_depth >= 0)) \
- __release_kernel_lock(); \
-} while (0)
-
-static inline int reacquire_kernel_lock(struct task_struct *task)
-{
- if (unlikely(task->lock_depth >= 0))
- return __reacquire_kernel_lock();
- return 0;
-}
-
-extern void __lockfunc
-_lock_kernel(const char *func, const char *file, int line)
-__acquires(kernel_lock);
-
-extern void __lockfunc
-_unlock_kernel(const char *func, const char *file, int line)
-__releases(kernel_lock);
-
-#define lock_kernel() do { \
- _lock_kernel(__func__, __FILE__, __LINE__); \
-} while (0)
-
-#define unlock_kernel() do { \
- _unlock_kernel(__func__, __FILE__, __LINE__); \
-} while (0)
-
-/*
- * Various legacy drivers don't really need the BKL in a specific
- * function, but they *do* need to know that the BKL became available.
- * This function just avoids wrapping a bunch of lock/unlock pairs
- * around code which doesn't really need it.
- */
-static inline void cycle_kernel_lock(void)
-{
- lock_kernel();
- unlock_kernel();
-}
-
-#else
-
-#ifdef CONFIG_BKL /* provoke build bug if not set */
-#define lock_kernel()
-#define unlock_kernel()
-#define cycle_kernel_lock() do { } while(0)
-#endif /* CONFIG_BKL */
-
-#define release_kernel_lock(task) do { } while(0)
-#define reacquire_kernel_lock(task) 0
-
-#endif /* CONFIG_LOCK_KERNEL */
-#endif /* __LINUX_SMPLOCK_H */
diff --git a/init/Kconfig b/init/Kconfig
index be788c0..a88d1c9 100644
--- a/init/Kconfig
+++ b/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
diff --git a/kernel/sched.c b/kernel/sched.c
index 18d38e4..827c170 100644
--- a/kernel/sched.c
+++ b/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 @@ need_resched:
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 @@ need_resched_nonpreemptible:

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)
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 2b97418..6f440d8 100644
--- a/lib/Kconfig.debug
+++ b/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
diff --git a/lib/Makefile b/lib/Makefile
index cbb774f..de6c609 100644
--- a/lib/Makefile
+++ b/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
diff --git a/lib/kernel_lock.c b/lib/kernel_lock.c
deleted file mode 100644
index d80e122..0000000
--- a/lib/kernel_lock.c
+++ /dev/null
@@ -1,136 +0,0 @@
-/*
- * lib/kernel_lock.c
- *
- * This is the traditional BKL - big kernel lock. Largely
- * relegated to obsolescence, but used by various less
- * important (or lazy) subsystems.
- */
-#include <linux/module.h>
-#include <linux/kallsyms.h>
-#include <linux/semaphore.h>
-#include <linux/smp_lock.h>
-
-/*
- * The 'big kernel lock'
- *
- * This spinlock is taken and released recursively by lock_kernel()
- * and unlock_kernel(). It is transparently dropped and reacquired
- * over schedule(). It is used to protect legacy code that hasn't
- * been migrated to a proper locking design yet.
- *
- * Don't use in new code.
- */
-static __cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(kernel_flag);
-
-
-/*
- * Acquire/release the underlying lock from the scheduler.
- *
- * This is called with preemption disabled, and should
- * return an error value if it cannot get the lock and
- * TIF_NEED_RESCHED gets set.
- *
- * If it successfully gets the lock, it should increment
- * the preemption count like any spinlock does.
- *
- * (This works on UP too - do_raw_spin_trylock will never
- * return false in that case)
- */
-int __lockfunc __reacquire_kernel_lock(void)
-{
- while (!do_raw_spin_trylock(&kernel_flag)) {
- if (need_resched())
- return -EAGAIN;
- cpu_relax();
- }
- preempt_disable();
- return 0;
-}
-
-void __lockfunc __release_kernel_lock(void)
-{
- do_raw_spin_unlock(&kernel_flag);
- preempt_enable_no_resched();
-}
-
-/*
- * These are the BKL spinlocks - we try to be polite about preemption.
- * If SMP is not on (ie UP preemption), this all goes away because the
- * do_raw_spin_trylock() will always succeed.
- */
-#ifdef CONFIG_PREEMPT
-static inline void __lock_kernel(void)
-{
- preempt_disable();
- if (unlikely(!do_raw_spin_trylock(&kernel_flag))) {
- /*
- * If preemption was disabled even before this
- * was called, there's nothing we can be polite
- * about - just spin.
- */
- if (preempt_count() > 1) {
- do_raw_spin_lock(&kernel_flag);
- return;
- }
-
- /*
- * Otherwise, let's wait for the kernel lock
- * with preemption enabled..
- */
- do {
- preempt_enable();
- while (raw_spin_is_locked(&kernel_flag))
- cpu_relax();
- preempt_disable();
- } while (!do_raw_spin_trylock(&kernel_flag));
- }
-}
-
-#else
-
-/*
- * Non-preemption case - just get the spinlock
- */
-static inline void __lock_kernel(void)
-{
- do_raw_spin_lock(&kernel_flag);
-}
-#endif
-
-static inline void __unlock_kernel(void)
-{
- /*
- * the BKL is not covered by lockdep, so we open-code the
- * unlocking sequence (and thus avoid the dep-chain ops):
- */
- do_raw_spin_unlock(&kernel_flag);
- preempt_enable();
-}
-
-/*
- * Getting the big kernel lock.
- *
- * This cannot happen asynchronously, so we only need to
- * worry about other CPU's.
- */
-void __lockfunc _lock_kernel(const char *func, const char *file, int line)
-{
- int depth = current->lock_depth + 1;
-
- if (likely(!depth)) {
- might_sleep();
- __lock_kernel();
- }
- current->lock_depth = depth;
-}
-
-void __lockfunc _unlock_kernel(const char *func, const char *file, int line)
-{
- BUG_ON(current->lock_depth < 0);
- if (likely(--current->lock_depth < 0))
- __unlock_kernel();
-}
-
-EXPORT_SYMBOL(_lock_kernel);
-EXPORT_SYMBOL(_unlock_kernel);
-
--
1.7.1

2011-03-03 07:38:25

by Andrew Hendry

[permalink] [raw]

Subject: Re: [PATCH 5/7] x25: remove the BKL

Looks good, put 8gig through it over the past few days and system stable.

Tested-by: Andrew Hendry <[email protected]>

On Wed, Mar 2, 2011 at 10:16 AM, David Miller <[email protected]> wrote:
> From: Arnd Bergmann <[email protected]>
> Date: Wed, ?2 Mar 2011 00:13:09 +0100
>
>> This replaces all instances of lock_kernel in x25
>> with lock_sock, taking care to release the socket
>> lock around sleeping functions (sock_alloc_send_skb
>> and skb_recv_datagram). It is not clear whether
>> this is a correct solution, but it seem to be what
>> other protocols do in the same situation.
>>
>> Includes a fix suggested by Eric Dumazet.
>>
>> Signed-off-by: Arnd Bergmann <[email protected]>
>
> Acked-by: David S. Miller <[email protected]>
>