Documentation/locking/seqlock.rst

8 Sequence counters are a reader-writer consistency mechanism with
9 lockless readers (read-only retry loops), and no writer starvation. They
15 read side critical section is even and the same sequence count value is
17 be copied out inside the read side critical section. If the sequence
24 the end of the write side critical section the sequence count becomes
27 A sequence counter write side critical section must never be preempted
28 or interrupted by read side sections. Otherwise the reader will spin for
30 interrupted writer. If that reader belongs to a real-time scheduling
43 multiple writers.  Write side critical sections must thus be serialized
44 by an external lock.
48 write side section. If the read section can be invoked from hardirq or
53 requirements of writer serialization and non-preemptibility, use
76 	/* ... [[write-side critical section]] ... */
85 		/* ... [[read-side critical section]] ... */
93 -----------------------------------------------------------------
95 As discussed at :ref:`seqcount_t`, sequence count write side critical
96 sections must be serialized and non-preemptible. This variant of
99 side critical sections are properly serialized.
104 injected at the beginning of the write side critical section to validate
108 protection is enforced in the write side function.
112   - ``seqcount_spinlock_t``
113   - ``seqcount_raw_spinlock_t``
114   - ``seqcount_rwlock_t``
115   - ``seqcount_mutex_t``
116   - ``seqcount_ww_mutex_t``
145 ----------------------------------------------
150 read path to safely interrupt its own write side critical section.
152 Use seqcount_latch_t when the write side sections cannot be protected
153 from interruption by readers. This is typically the case when the read
154 side can be invoked from NMI handlers.
165 embedded spinlock for writer serialization and non-preemptibility.
167 If the read side section can be invoked from hardirq or softirq context,
168 use the write side function variants which disable interrupts or bottom
189 	/* ... [[write-side critical section]] ... */
196    retry if a writer is in progress by detecting change in the sequence
202 		/* ... [[read-side critical section]] ... */
213 	/* ... [[read-side critical section]] ... */
230 		/* ... [[read-side critical section]] ... */
239 .. kernel-doc:: include/linux/seqlock.h