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-rw-r--r--Documentation/locking/seqlock.rst52
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diff --git a/Documentation/locking/seqlock.rst b/Documentation/locking/seqlock.rst
index 366dd368d90a..62c5ad98c11c 100644
--- a/Documentation/locking/seqlock.rst
+++ b/Documentation/locking/seqlock.rst
@@ -87,6 +87,58 @@ Read path::
} while (read_seqcount_retry(&foo_seqcount, seq));
+.. _seqcount_locktype_t:
+
+Sequence counters with associated locks (``seqcount_LOCKTYPE_t``)
+-----------------------------------------------------------------
+
+As discussed at :ref:`seqcount_t`, sequence count write side critical
+sections must be serialized and non-preemptible. This variant of
+sequence counters associate the lock used for writer serialization at
+initialization time, which enables lockdep to validate that the write
+side critical sections are properly serialized.
+
+This lock association is a NOOP if lockdep is disabled and has neither
+storage nor runtime overhead. If lockdep is enabled, the lock pointer is
+stored in struct seqcount and lockdep's "lock is held" assertions are
+injected at the beginning of the write side critical section to validate
+that it is properly protected.
+
+For lock types which do not implicitly disable preemption, preemption
+protection is enforced in the write side function.
+
+The following sequence counters with associated locks are defined:
+
+ - ``seqcount_spinlock_t``
+ - ``seqcount_raw_spinlock_t``
+ - ``seqcount_rwlock_t``
+ - ``seqcount_mutex_t``
+ - ``seqcount_ww_mutex_t``
+
+The plain seqcount read and write APIs branch out to the specific
+seqcount_LOCKTYPE_t implementation at compile-time. This avoids kernel
+API explosion per each new seqcount LOCKTYPE.
+
+Initialization (replace "LOCKTYPE" with one of the supported locks)::
+
+ /* dynamic */
+ seqcount_LOCKTYPE_t foo_seqcount;
+ seqcount_LOCKTYPE_init(&foo_seqcount, &lock);
+
+ /* static */
+ static seqcount_LOCKTYPE_t foo_seqcount =
+ SEQCNT_LOCKTYPE_ZERO(foo_seqcount, &lock);
+
+ /* C99 struct init */
+ struct {
+ .seq = SEQCNT_LOCKTYPE_ZERO(foo.seq, &lock),
+ } foo;
+
+Write path: same as in :ref:`seqcount_t`, while running from a context
+with the associated LOCKTYPE lock acquired.
+
+Read path: same as in :ref:`seqcount_t`.
+
.. _seqlock_t:
Sequential locks (``seqlock_t``)