docs: RCU: Convert lockdep.txt to ReST

- Add a SPDX header;
- Adjust document title;
- Mark literal blocks as such;
- Add it to RCU/index.rst.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

1 files changed, 0 insertions, 112 deletions

diff --git a/Documentation/RCU/lockdep.txt b/Documentation/RCU/lockdep.txt
deleted file mode 100644
index 89db949eeca0..000000000000
--- a/Documentation/RCU/lockdep.txt
+++ /dev/null
@@ -1,112 +0,0 @@
-RCU and lockdep checking
-
-All flavors of RCU have lockdep checking available, so that lockdep is
-aware of when each task enters and leaves any flavor of RCU read-side
-critical section.  Each flavor of RCU is tracked separately (but note
-that this is not the case in 2.6.32 and earlier).  This allows lockdep's
-tracking to include RCU state, which can sometimes help when debugging
-deadlocks and the like.
-
-In addition, RCU provides the following primitives that check lockdep's
-state:
-
-	rcu_read_lock_held() for normal RCU.
-	rcu_read_lock_bh_held() for RCU-bh.
-	rcu_read_lock_sched_held() for RCU-sched.
-	srcu_read_lock_held() for SRCU.
-
-These functions are conservative, and will therefore return 1 if they
-aren't certain (for example, if CONFIG_DEBUG_LOCK_ALLOC is not set).
-This prevents things like WARN_ON(!rcu_read_lock_held()) from giving false
-positives when lockdep is disabled.
-
-In addition, a separate kernel config parameter CONFIG_PROVE_RCU enables
-checking of rcu_dereference() primitives:
-
-	rcu_dereference(p):
-		Check for RCU read-side critical section.
-	rcu_dereference_bh(p):
-		Check for RCU-bh read-side critical section.
-	rcu_dereference_sched(p):
-		Check for RCU-sched read-side critical section.
-	srcu_dereference(p, sp):
-		Check for SRCU read-side critical section.
-	rcu_dereference_check(p, c):
-		Use explicit check expression "c" along with
-		rcu_read_lock_held().  This is useful in code that is
-		invoked by both RCU readers and updaters.
-	rcu_dereference_bh_check(p, c):
-		Use explicit check expression "c" along with
-		rcu_read_lock_bh_held().  This is useful in code that
-		is invoked by both RCU-bh readers and updaters.
-	rcu_dereference_sched_check(p, c):
-		Use explicit check expression "c" along with
-		rcu_read_lock_sched_held().  This is useful in code that
-		is invoked by both RCU-sched readers and updaters.
-	srcu_dereference_check(p, c):
-		Use explicit check expression "c" along with
-		srcu_read_lock_held()().  This is useful in code that
-		is invoked by both SRCU readers and updaters.
-	rcu_dereference_raw(p):
-		Don't check.  (Use sparingly, if at all.)
-	rcu_dereference_protected(p, c):
-		Use explicit check expression "c", and omit all barriers
-		and compiler constraints.  This is useful when the data
-		structure cannot change, for example, in code that is
-		invoked only by updaters.
-	rcu_access_pointer(p):
-		Return the value of the pointer and omit all barriers,
-		but retain the compiler constraints that prevent duplicating
-		or coalescsing.  This is useful when when testing the
-		value of the pointer itself, for example, against NULL.
-
-The rcu_dereference_check() check expression can be any boolean
-expression, but would normally include a lockdep expression.  However,
-any boolean expression can be used.  For a moderately ornate example,
-consider the following:
-
-	file = rcu_dereference_check(fdt->fd[fd],
-				     lockdep_is_held(&files->file_lock) ||
-				     atomic_read(&files->count) == 1);
-
-This expression picks up the pointer "fdt->fd[fd]" in an RCU-safe manner,
-and, if CONFIG_PROVE_RCU is configured, verifies that this expression
-is used in:
-
-1.	An RCU read-side critical section (implicit), or
-2.	with files->file_lock held, or
-3.	on an unshared files_struct.
-
-In case (1), the pointer is picked up in an RCU-safe manner for vanilla
-RCU read-side critical sections, in case (2) the ->file_lock prevents
-any change from taking place, and finally, in case (3) the current task
-is the only task accessing the file_struct, again preventing any change
-from taking place.  If the above statement was invoked only from updater
-code, it could instead be written as follows:
-
-	file = rcu_dereference_protected(fdt->fd[fd],
-					 lockdep_is_held(&files->file_lock) ||
-					 atomic_read(&files->count) == 1);
-
-This would verify cases #2 and #3 above, and furthermore lockdep would
-complain if this was used in an RCU read-side critical section unless one
-of these two cases held.  Because rcu_dereference_protected() omits all
-barriers and compiler constraints, it generates better code than do the
-other flavors of rcu_dereference().  On the other hand, it is illegal
-to use rcu_dereference_protected() if either the RCU-protected pointer
-or the RCU-protected data that it points to can change concurrently.
-
-Like rcu_dereference(), when lockdep is enabled, RCU list and hlist
-traversal primitives check for being called from within an RCU read-side
-critical section.  However, a lockdep expression can be passed to them
-as a additional optional argument.  With this lockdep expression, these
-traversal primitives will complain only if the lockdep expression is
-false and they are called from outside any RCU read-side critical section.
-
-For example, the workqueue for_each_pwq() macro is intended to be used
-either within an RCU read-side critical section or with wq->mutex held.
-It is thus implemented as follows:
-
-	#define for_each_pwq(pwq, wq)
-		list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node,
-					lock_is_held(&(wq->mutex).dep_map))