From 78305de2f99e9f43ab860dd95bb430b20e26c695 Mon Sep 17 00:00:00 2001 From: Matthew Wilcox Date: Wed, 23 Apr 2008 07:20:41 -0400 Subject: Remove mention of semaphores from kernel-locking Since the consensus seems to be to eliminate semaphores where possible, we shouldn't be educating people about how to use them as locks. Use mutexes instead. Semaphores should be described in a separate document if we end up keeping them. Signed-off-by: Matthew Wilcox Acked-by: Rusty Russell --- Documentation/DocBook/kernel-locking.tmpl | 57 +++++++++++++------------------ 1 file changed, 24 insertions(+), 33 deletions(-) diff --git a/Documentation/DocBook/kernel-locking.tmpl b/Documentation/DocBook/kernel-locking.tmpl index 2510763295d..084f6ad7b7a 100644 --- a/Documentation/DocBook/kernel-locking.tmpl +++ b/Documentation/DocBook/kernel-locking.tmpl @@ -219,10 +219,10 @@ - Three Main Types of Kernel Locks: Spinlocks, Mutexes and Semaphores + Two Main Types of Kernel Locks: Spinlocks and Mutexes - There are three main types of kernel locks. The fundamental type + There are two main types of kernel locks. The fundamental type is the spinlock (include/asm/spinlock.h), which is a very simple single-holder lock: if you can't get the @@ -239,14 +239,6 @@ can't sleep (see ), and so have to use a spinlock instead. - - The third type is a semaphore - (include/linux/semaphore.h): it - can have more than one holder at any time (the number decided at - initialization time), although it is most commonly used as a - single-holder lock (a mutex). If you can't get a semaphore, your - task will be suspended and later on woken up - just like for mutexes. - Neither type of lock is recursive: see . @@ -278,7 +270,7 @@ - Semaphores still exist, because they are required for + Mutexes still exist, because they are required for synchronization between user contexts, as we will see below. @@ -289,18 +281,17 @@ If you have a data structure which is only ever accessed from - user context, then you can use a simple semaphore - (linux/linux/semaphore.h) to protect it. This - is the most trivial case: you initialize the semaphore to the number - of resources available (usually 1), and call - down_interruptible() to grab the semaphore, and - up() to release it. There is also a - down(), which should be avoided, because it + user context, then you can use a simple mutex + (include/linux/mutex.h) to protect it. This + is the most trivial case: you initialize the mutex. Then you can + call mutex_lock_interruptible() to grab the mutex, + and mutex_unlock() to release it. There is also a + mutex_lock(), which should be avoided, because it will not return if a signal is received. - Example: linux/net/core/netfilter.c allows + Example: net/netfilter/nf_sockopt.c allows registration of new setsockopt() and getsockopt() calls, with nf_register_sockopt(). Registration and @@ -515,7 +506,7 @@ If you are in a process context (any syscall) and want to - lock other process out, use a semaphore. You can take a semaphore + lock other process out, use a mutex. You can take a mutex and sleep (copy_from_user*( or kmalloc(x,GFP_KERNEL)). @@ -662,7 +653,7 @@ SLBH SLBH SLBH -DI +MLI None @@ -692,8 +683,8 @@ spin_lock_bh -DI -down_interruptible +MLI +mutex_lock_interruptible @@ -1310,7 +1301,7 @@ as Alan Cox says, Lock data, not code. There is a coding bug where a piece of code tries to grab a spinlock twice: it will spin forever, waiting for the lock to - be released (spinlocks, rwlocks and semaphores are not + be released (spinlocks, rwlocks and mutexes are not recursive in Linux). This is trivial to diagnose: not a stay-up-five-nights-talk-to-fluffy-code-bunnies kind of problem. @@ -1335,7 +1326,7 @@ as Alan Cox says, Lock data, not code. This complete lockup is easy to diagnose: on SMP boxes the - watchdog timer or compiling with DEBUG_SPINLOCKS set + watchdog timer or compiling with DEBUG_SPINLOCK set (include/linux/spinlock.h) will show this up immediately when it happens. @@ -1558,7 +1549,7 @@ the amount of locking which needs to be done. Read/Write Lock Variants - Both spinlocks and semaphores have read/write variants: + Both spinlocks and mutexes have read/write variants: rwlock_t and struct rw_semaphore. These divide users into two classes: the readers and the writers. If you are only reading the data, you can get a read lock, but to write to @@ -1681,7 +1672,7 @@ the amount of locking which needs to be done. #include <linux/slab.h> #include <linux/string.h> +#include <linux/rcupdate.h> - #include <linux/semaphore.h> + #include <linux/mutex.h> #include <asm/errno.h> struct object @@ -1913,7 +1904,7 @@ machines due to caching. - put_user() + put_user() @@ -1927,13 +1918,13 @@ machines due to caching. - down_interruptible() and - down() + mutex_lock_interruptible() and + mutex_lock() - There is a down_trylock() which can be + There is a mutex_trylock() which can be used inside interrupt context, as it will not sleep. - up() will also never sleep. + mutex_unlock() will also never sleep. @@ -2023,7 +2014,7 @@ machines due to caching. Prior to 2.5, or when CONFIG_PREEMPT is unset, processes in user context inside the kernel would not - preempt each other (ie. you had that CPU until you have it up, + preempt each other (ie. you had that CPU until you gave it up, except for interrupts). With the addition of CONFIG_PREEMPT in 2.5.4, this changed: when in user context, higher priority tasks can "cut in": spinlocks -- cgit From 0f17e4c796e89d1f69f13b653aba60e6ccfb8ae0 Mon Sep 17 00:00:00 2001 From: Matthew Wilcox Date: Thu, 24 Jul 2008 08:30:48 -0400 Subject: Add missing semaphore.h includes These files use semaphores but don't include semaphore.h Signed-off-by: Matthew Wilcox Acked-by: Geert Uytterhoeven --- drivers/input/keyboard/hil_kbd.c | 1 + drivers/input/misc/hp_sdc_rtc.c | 1 + drivers/input/serio/hp_sdc.c | 1 + 3 files changed, 3 insertions(+) diff --git a/drivers/input/keyboard/hil_kbd.c b/drivers/input/keyboard/hil_kbd.c index adbf29f0169..71c1971abf8 100644 --- a/drivers/input/keyboard/hil_kbd.c +++ b/drivers/input/keyboard/hil_kbd.c @@ -37,6 +37,7 @@ #include #include #include +#include #include #include diff --git a/drivers/input/misc/hp_sdc_rtc.c b/drivers/input/misc/hp_sdc_rtc.c index 49d8abfe38f..daa9d422033 100644 --- a/drivers/input/misc/hp_sdc_rtc.c +++ b/drivers/input/misc/hp_sdc_rtc.c @@ -44,6 +44,7 @@ #include #include #include +#include MODULE_AUTHOR("Brian S. Julin "); MODULE_DESCRIPTION("HP i8042 SDC + MSM-58321 RTC Driver"); diff --git a/drivers/input/serio/hp_sdc.c b/drivers/input/serio/hp_sdc.c index 7b233a492ad..aad664d5259 100644 --- a/drivers/input/serio/hp_sdc.c +++ b/drivers/input/serio/hp_sdc.c @@ -67,6 +67,7 @@ #include #include #include +#include #include #include #include -- cgit From 6310e472717ed736c9bff9840febb71f7bb400ed Mon Sep 17 00:00:00 2001 From: Matthew Wilcox Date: Thu, 24 Jul 2008 08:08:09 -0400 Subject: Remove use of asm/semaphore.h Change to use linux/semaphore.h Signed-off-by: Matthew Wilcox --- arch/arm/mach-ns9xxx/clock.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm/mach-ns9xxx/clock.c b/arch/arm/mach-ns9xxx/clock.c index f8639161068..44ed20d4a38 100644 --- a/arch/arm/mach-ns9xxx/clock.c +++ b/arch/arm/mach-ns9xxx/clock.c @@ -14,8 +14,8 @@ #include #include #include +#include -#include #include "clock.h" static LIST_HEAD(clocks); -- cgit From 2351ec533ed0dd56052ab96988d2161d5ecc8ed9 Mon Sep 17 00:00:00 2001 From: Matthew Wilcox Date: Thu, 24 Jul 2008 08:09:32 -0400 Subject: Remove asm/semaphore.h All users have now been converted to linux/semaphore.h and we don't need to keep these files around any longer. Signed-off-by: Matthew Wilcox --- Documentation/feature-removal-schedule.txt | 8 -------- include/asm-alpha/semaphore.h | 1 - include/asm-arm/semaphore.h | 1 - include/asm-avr32/semaphore.h | 1 - include/asm-blackfin/semaphore.h | 1 - include/asm-cris/semaphore.h | 1 - include/asm-frv/semaphore.h | 1 - include/asm-h8300/semaphore.h | 1 - include/asm-ia64/semaphore.h | 1 - include/asm-m32r/semaphore.h | 1 - include/asm-m68k/semaphore.h | 1 - include/asm-m68knommu/semaphore.h | 1 - include/asm-mips/semaphore.h | 1 - include/asm-mn10300/semaphore.h | 1 - include/asm-parisc/semaphore.h | 1 - include/asm-powerpc/semaphore.h | 1 - include/asm-s390/semaphore.h | 1 - include/asm-sh/semaphore.h | 1 - include/asm-sparc/semaphore.h | 1 - include/asm-sparc64/semaphore.h | 1 - include/asm-um/semaphore.h | 1 - include/asm-v850/semaphore.h | 1 - include/asm-x86/semaphore.h | 1 - include/asm-xtensa/semaphore.h | 1 - 24 files changed, 31 deletions(-) delete mode 100644 include/asm-alpha/semaphore.h delete mode 100644 include/asm-arm/semaphore.h delete mode 100644 include/asm-avr32/semaphore.h delete mode 100644 include/asm-blackfin/semaphore.h delete mode 100644 include/asm-cris/semaphore.h delete mode 100644 include/asm-frv/semaphore.h delete mode 100644 include/asm-h8300/semaphore.h delete mode 100644 include/asm-ia64/semaphore.h delete mode 100644 include/asm-m32r/semaphore.h delete mode 100644 include/asm-m68k/semaphore.h delete mode 100644 include/asm-m68knommu/semaphore.h delete mode 100644 include/asm-mips/semaphore.h delete mode 100644 include/asm-mn10300/semaphore.h delete mode 100644 include/asm-parisc/semaphore.h delete mode 100644 include/asm-powerpc/semaphore.h delete mode 100644 include/asm-s390/semaphore.h delete mode 100644 include/asm-sh/semaphore.h delete mode 100644 include/asm-sparc/semaphore.h delete mode 100644 include/asm-sparc64/semaphore.h delete mode 100644 include/asm-um/semaphore.h delete mode 100644 include/asm-v850/semaphore.h delete mode 100644 include/asm-x86/semaphore.h delete mode 100644 include/asm-xtensa/semaphore.h diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt index 9f73587219e..09c4a1efb8e 100644 --- a/Documentation/feature-removal-schedule.txt +++ b/Documentation/feature-removal-schedule.txt @@ -300,14 +300,6 @@ Who: ocfs2-devel@oss.oracle.com --------------------------- -What: asm/semaphore.h -When: 2.6.26 -Why: Implementation became generic; users should now include - linux/semaphore.h instead. -Who: Matthew Wilcox - ---------------------------- - What: SCTP_GET_PEER_ADDRS_NUM_OLD, SCTP_GET_PEER_ADDRS_OLD, SCTP_GET_LOCAL_ADDRS_NUM_OLD, SCTP_GET_LOCAL_ADDRS_OLD When: June 2009 diff --git a/include/asm-alpha/semaphore.h b/include/asm-alpha/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-alpha/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-arm/semaphore.h b/include/asm-arm/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-arm/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-avr32/semaphore.h b/include/asm-avr32/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-avr32/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-blackfin/semaphore.h b/include/asm-blackfin/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-blackfin/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-cris/semaphore.h b/include/asm-cris/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-cris/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-frv/semaphore.h b/include/asm-frv/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-frv/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-h8300/semaphore.h b/include/asm-h8300/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-h8300/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-ia64/semaphore.h b/include/asm-ia64/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-ia64/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-m32r/semaphore.h b/include/asm-m32r/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-m32r/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-m68k/semaphore.h b/include/asm-m68k/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-m68k/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-m68knommu/semaphore.h b/include/asm-m68knommu/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-m68knommu/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-mips/semaphore.h b/include/asm-mips/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-mips/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-mn10300/semaphore.h b/include/asm-mn10300/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-mn10300/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-parisc/semaphore.h b/include/asm-parisc/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-parisc/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-powerpc/semaphore.h b/include/asm-powerpc/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-powerpc/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-s390/semaphore.h b/include/asm-s390/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-s390/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-sh/semaphore.h b/include/asm-sh/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-sh/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-sparc/semaphore.h b/include/asm-sparc/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-sparc/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-sparc64/semaphore.h b/include/asm-sparc64/semaphore.h deleted file mode 100644 index 39362afde5f..00000000000 --- a/include/asm-sparc64/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-um/semaphore.h b/include/asm-um/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-um/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-v850/semaphore.h b/include/asm-v850/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-v850/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-x86/semaphore.h b/include/asm-x86/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-x86/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include diff --git a/include/asm-xtensa/semaphore.h b/include/asm-xtensa/semaphore.h deleted file mode 100644 index d9b2034ed1d..00000000000 --- a/include/asm-xtensa/semaphore.h +++ /dev/null @@ -1 +0,0 @@ -#include -- cgit From b552068999b0b05087c454e525b30b785c79dc9b Mon Sep 17 00:00:00 2001 From: Matthew Wilcox Date: Wed, 23 Apr 2008 10:07:27 -0400 Subject: Remove __DECLARE_SEMAPHORE_GENERIC There are no users of __DECLARE_SEMAPHORE_GENERIC in the kernel Signed-off-by: Matthew Wilcox --- include/linux/semaphore.h | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/include/linux/semaphore.h b/include/linux/semaphore.h index 9cae64b00d6..7415839ac89 100644 --- a/include/linux/semaphore.h +++ b/include/linux/semaphore.h @@ -26,10 +26,8 @@ struct semaphore { .wait_list = LIST_HEAD_INIT((name).wait_list), \ } -#define __DECLARE_SEMAPHORE_GENERIC(name, count) \ - struct semaphore name = __SEMAPHORE_INITIALIZER(name, count) - -#define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name, 1) +#define DECLARE_MUTEX(name) \ + struct semaphore name = __SEMAPHORE_INITIALIZER(name, 1) static inline void sema_init(struct semaphore *sem, int val) { -- cgit