forked from Minki/linux
Merge branch 'semaphore' of git://git.kernel.org/pub/scm/linux/kernel/git/willy/misc
* 'semaphore' of git://git.kernel.org/pub/scm/linux/kernel/git/willy/misc: Remove __DECLARE_SEMAPHORE_GENERIC Remove asm/semaphore.h Remove use of asm/semaphore.h Add missing semaphore.h includes Remove mention of semaphores from kernel-locking
This commit is contained in:
Linus Torvalds
commit
7540081c6b
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@ -219,10 +219,10 @@
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</para>
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<sect1 id="lock-intro">
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<title>Three Main Types of Kernel Locks: Spinlocks, Mutexes and Semaphores</title>
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<title>Two Main Types of Kernel Locks: Spinlocks and Mutexes</title>
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<para>
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There are three main types of kernel locks. The fundamental type
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There are two main types of kernel locks. The fundamental type
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is the spinlock
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(<filename class="headerfile">include/asm/spinlock.h</filename>),
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which is a very simple single-holder lock: if you can't get the
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@ -239,14 +239,6 @@
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can't sleep (see <xref linkend="sleeping-things"/>), and so have to
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use a spinlock instead.
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</para>
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<para>
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The third type is a semaphore
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(<filename class="headerfile">include/linux/semaphore.h</filename>): it
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can have more than one holder at any time (the number decided at
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initialization time), although it is most commonly used as a
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single-holder lock (a mutex). If you can't get a semaphore, your
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task will be suspended and later on woken up - just like for mutexes.
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</para>
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<para>
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Neither type of lock is recursive: see
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<xref linkend="deadlock"/>.
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@ -278,7 +270,7 @@
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</para>
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<para>
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Semaphores still exist, because they are required for
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Mutexes still exist, because they are required for
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synchronization between <firstterm linkend="gloss-usercontext">user
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contexts</firstterm>, as we will see below.
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</para>
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@ -289,18 +281,17 @@
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<para>
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If you have a data structure which is only ever accessed from
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user context, then you can use a simple semaphore
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(<filename>linux/linux/semaphore.h</filename>) to protect it. This
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is the most trivial case: you initialize the semaphore to the number
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of resources available (usually 1), and call
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<function>down_interruptible()</function> to grab the semaphore, and
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<function>up()</function> to release it. There is also a
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<function>down()</function>, which should be avoided, because it
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user context, then you can use a simple mutex
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(<filename>include/linux/mutex.h</filename>) to protect it. This
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is the most trivial case: you initialize the mutex. Then you can
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call <function>mutex_lock_interruptible()</function> to grab the mutex,
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and <function>mutex_unlock()</function> to release it. There is also a
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<function>mutex_lock()</function>, which should be avoided, because it
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will not return if a signal is received.
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</para>
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<para>
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Example: <filename>linux/net/core/netfilter.c</filename> allows
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Example: <filename>net/netfilter/nf_sockopt.c</filename> allows
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registration of new <function>setsockopt()</function> and
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<function>getsockopt()</function> calls, with
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<function>nf_register_sockopt()</function>. Registration and
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@ -515,7 +506,7 @@
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<listitem>
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<para>
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If you are in a process context (any syscall) and want to
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lock other process out, use a semaphore. You can take a semaphore
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lock other process out, use a mutex. You can take a mutex
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and sleep (<function>copy_from_user*(</function> or
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<function>kmalloc(x,GFP_KERNEL)</function>).
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</para>
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@ -662,7 +653,7 @@
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<entry>SLBH</entry>
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<entry>SLBH</entry>
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<entry>SLBH</entry>
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<entry>DI</entry>
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<entry>MLI</entry>
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<entry>None</entry>
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</row>
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@ -692,8 +683,8 @@
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<entry>spin_lock_bh</entry>
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</row>
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<row>
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<entry>DI</entry>
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<entry>down_interruptible</entry>
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<entry>MLI</entry>
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<entry>mutex_lock_interruptible</entry>
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</row>
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</tbody>
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@ -1310,7 +1301,7 @@ as Alan Cox says, <quote>Lock data, not code</quote>.
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<para>
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There is a coding bug where a piece of code tries to grab a
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spinlock twice: it will spin forever, waiting for the lock to
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be released (spinlocks, rwlocks and semaphores are not
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be released (spinlocks, rwlocks and mutexes are not
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recursive in Linux). This is trivial to diagnose: not a
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stay-up-five-nights-talk-to-fluffy-code-bunnies kind of
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problem.
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@ -1335,7 +1326,7 @@ as Alan Cox says, <quote>Lock data, not code</quote>.
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<para>
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This complete lockup is easy to diagnose: on SMP boxes the
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watchdog timer or compiling with <symbol>DEBUG_SPINLOCKS</symbol> set
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watchdog timer or compiling with <symbol>DEBUG_SPINLOCK</symbol> set
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(<filename>include/linux/spinlock.h</filename>) will show this up
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immediately when it happens.
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</para>
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@ -1558,7 +1549,7 @@ the amount of locking which needs to be done.
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<title>Read/Write Lock Variants</title>
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<para>
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Both spinlocks and semaphores have read/write variants:
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Both spinlocks and mutexes have read/write variants:
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<type>rwlock_t</type> and <structname>struct rw_semaphore</structname>.
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These divide users into two classes: the readers and the writers. If
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you are only reading the data, you can get a read lock, but to write to
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@ -1681,7 +1672,7 @@ the amount of locking which needs to be done.
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#include <linux/slab.h>
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#include <linux/string.h>
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+#include <linux/rcupdate.h>
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#include <linux/semaphore.h>
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#include <linux/mutex.h>
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#include <asm/errno.h>
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struct object
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@ -1927,13 +1918,13 @@ machines due to caching.
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<listitem>
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<para>
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<function>down_interruptible()</function> and
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<function>down()</function>
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<function>mutex_lock_interruptible()</function> and
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<function>mutex_lock()</function>
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</para>
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<para>
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There is a <function>down_trylock()</function> which can be
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There is a <function>mutex_trylock()</function> which can be
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used inside interrupt context, as it will not sleep.
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<function>up()</function> will also never sleep.
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<function>mutex_unlock()</function> will also never sleep.
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</para>
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</listitem>
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</itemizedlist>
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@ -2023,7 +2014,7 @@ machines due to caching.
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<para>
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Prior to 2.5, or when <symbol>CONFIG_PREEMPT</symbol> is
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unset, processes in user context inside the kernel would not
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preempt each other (ie. you had that CPU until you have it up,
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preempt each other (ie. you had that CPU until you gave it up,
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except for interrupts). With the addition of
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<symbol>CONFIG_PREEMPT</symbol> in 2.5.4, this changed: when
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in user context, higher priority tasks can "cut in": spinlocks
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@ -300,14 +300,6 @@ Who: ocfs2-devel@oss.oracle.com
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---------------------------
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What: asm/semaphore.h
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When: 2.6.26
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Why: Implementation became generic; users should now include
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linux/semaphore.h instead.
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Who: Matthew Wilcox <willy@linux.intel.com>
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---------------------------
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What: SCTP_GET_PEER_ADDRS_NUM_OLD, SCTP_GET_PEER_ADDRS_OLD,
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SCTP_GET_LOCAL_ADDRS_NUM_OLD, SCTP_GET_LOCAL_ADDRS_OLD
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When: June 2009
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@ -14,8 +14,8 @@
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#include <linux/clk.h>
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#include <linux/string.h>
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#include <linux/platform_device.h>
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#include <linux/semaphore.h>
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#include <asm/semaphore.h>
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#include "clock.h"
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static LIST_HEAD(clocks);
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@ -37,6 +37,7 @@
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/semaphore.h>
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#include <linux/slab.h>
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#include <linux/pci_ids.h>
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@ -44,6 +44,7 @@
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#include <linux/proc_fs.h>
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#include <linux/poll.h>
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#include <linux/rtc.h>
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#include <linux/semaphore.h>
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MODULE_AUTHOR("Brian S. Julin <bri@calyx.com>");
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MODULE_DESCRIPTION("HP i8042 SDC + MSM-58321 RTC Driver");
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@ -67,6 +67,7 @@
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#include <linux/module.h>
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#include <linux/ioport.h>
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#include <linux/time.h>
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#include <linux/semaphore.h>
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#include <linux/slab.h>
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#include <linux/hil.h>
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <asm-sparc/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -1 +0,0 @@
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#include <linux/semaphore.h>
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@ -26,10 +26,8 @@ struct semaphore {
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.wait_list = LIST_HEAD_INIT((name).wait_list), \
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}
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#define __DECLARE_SEMAPHORE_GENERIC(name, count) \
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struct semaphore name = __SEMAPHORE_INITIALIZER(name, count)
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#define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name, 1)
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#define DECLARE_MUTEX(name) \
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struct semaphore name = __SEMAPHORE_INITIALIZER(name, 1)
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static inline void sema_init(struct semaphore *sem, int val)
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{
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