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41 .Nd enter and exit a critical section
49 .Fn crit_enter_gd "globaldata_t gd"
51 .Fn crit_exit_gd "globaldata_t gd"
53 .Fn crit_enter_id "const char *id"
55 .Fn crit_exit_id "const char *id"
61 functions are used to enter and exit a critical section of code.
62 Entering a critical section will disallow preemption of the currently
63 running thread on the current CPU for the duration of the critical section.
64 While a critical section is active, interrupts and IPIs are also prevented
65 from executing on the current CPU.
66 Instead, the interrupt code marks the interrupt as deferred and immediately
67 returns (without scheduling any interrupt thread).
68 If an interrupt or an IPI is deferred in this way, it will be processed upon
69 leaving the critical section.
71 It is possible for a thread to sleep while holding a critical section,
72 however this results in the critical section being given up for the time of
73 the sleep and being reacquired after waking up.
75 If the current CPU's globaldata pointer is available,
79 may be used to reduce the amount of generated code.
81 Critical sections are per-CPU entities.
82 They are typically used to interlock operations local to the CPU.
83 A critical section on one CPU will not prevent an interrupt or IPI from
84 occurring on some other CPU.
85 If cross-CPU interlocks are required the more heavy weight
89 lock is recommended instead.
91 Unlike spinlocks and serializer locks, critical sections can be nested.
92 .Sh DEBUGGING CRITICAL SECTIONS
94 .Dv DEBUG_CRIT_SECTIONS
97 calls that are made from a different function than the
99 that they are unnesting.
104 functions can be used to specify a fixed ID in cases where this is done
106 Identifiers must be string pointers but the debug code only checks the
107 pointer address, it does not do a
111 The critical section implementation is in
112 .Pa /sys/sys/thread2.h .
118 These functions were introduced in