1.\" 2.\" Copyright (c) 2006 The DragonFly Project. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in 12.\" the documentation and/or other materials provided with the 13.\" distribution. 14.\" 3. Neither the name of The DragonFly Project nor the names of its 15.\" contributors may be used to endorse or promote products derived 16.\" from this software without specific, prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 19.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 20.\" LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 21.\" FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 22.\" COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 23.\" INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING, 24.\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 25.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 26.\" AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 27.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 28.\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" $DragonFly: src/share/man/man9/crit_enter.9,v 1.2 2007/05/13 20:29:48 hasso Exp $ 32.\" 33.Dd July 5, 2006 34.Dt CRIT_ENTER 9 35.Os 36.Sh NAME 37.Nm crit_enter , 38.Nm crit_enter_gd , 39.Nm crit_enter_id , 40.Nm crit_exit , 41.Nm crit_exit_gd , 42.Nm crit_exit_id 43.Nd enter and exit a critical section 44.Sh SYNOPSIS 45.In sys/thread2.h 46.Ft void 47.Fn crit_enter "void" 48.Ft void 49.Fn crit_exit "void" 50.Ft void 51.Fn crit_enter_gd "globaldata_t gd" 52.Ft void 53.Fn crit_exit_gd "globaldata_t gd" 54.Ft void 55.Fn crit_enter_id "const char *id" 56.Ft void 57.Fn crit_exit_id "const char *id" 58.Sh DESCRIPTION 59The 60.Fn crit_enter 61and 62.Fn crit_exit 63functions are used to enter and exit a critical section of code. 64While a critical section is active, interrupts and IPIs are prevented from 65executing on the current CPU. 66Instead, the interrupt code marks the interrupt as deferred and immediately 67returns. 68It is possible for a thread to sleep while holding a critical section, 69however this results in the critical section being given up for the time of 70the sleep and being reacquired after waking up. 71.Pp 72If the current CPU's globaldata pointer is available, 73.Fn crit_enter_gd 74and 75.Fn crit_exit_gd 76may be used to reduce the amount of generated code. 77.Pp 78Critical sections are per-CPU entities. 79A critical section on one CPU will not prevent an interrupt or IPI from 80occurring on some other CPU. 81If cross-CPU interlocks are required the more heavy weight 82.Xr spinlock 9 83or 84.Xr serializer 9 85lock is recommended instead. 86.Pp 87Unlike spinlocks and serializer locks, critical sections can be nested. 88.Sh DEBUGGING CRITICAL SECTIONS 89Kernels compiled with 90.Dv DEBUG_CRIT_SECTIONS 91will report any 92.Fn crit_exit 93calls that are made from a different function than the 94.Fn crit_enter 95that they are unnesting. 96The 97.Fn crit_enter_id 98and 99.Fn crit_exit_id 100functions can be used to specify a fixed ID in cases where this is done 101on purpose. 102Identifiers must be string pointers but the debug code only checks the 103pointer address, it does not do a 104.Fn strcmp 105to validate the ID. 106.Sh SEE ALSO 107.Xr serializer 9 , 108.Xr spinlock 9 109.Sh HISTORY 110These functions were introduced in 111.Dx 1.0 . 112