[PATCH 1/2 v2] cleanup: Add cond_guard() to conditional guards

[Fabio M. De Francesco]

Add cond_guard() macro to conditional guards.

cond_guard() is a guard to be used with the conditional variants of locks,
like down_read_trylock() or mutex_lock_interruptible().

It takes a statement (or more statements in a block) that is passed to its
second argument. That statement (or block) is executed if waiting for a
lock is interrupted or if a _trylock() fails in case of contention.

Usage example:

	cond_guard(rwsem_read_try, { printk(...); return 0; }, &semaphore);

Consistently with the other guards, locks are unlocked at the exit of the
scope where cond_guard() is called.

Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Suggested-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Suggested-by: Ira Weiny <ira.weiny@xxxxxxxxx>
Signed-off-by: Fabio M. De Francesco <fabio.maria.de.francesco@xxxxxxxxxxxxxxx>
---
 include/linux/cleanup.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h
index c2d09bc4f976..88af56600325 100644
--- a/include/linux/cleanup.h
+++ b/include/linux/cleanup.h
@@ -134,6 +134,16 @@ static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \
  *	an anonymous instance of the (guard) class, not recommended for
  *	conditional locks.
  *
+ * cond_guard(name, fail, args...):
+ *	a guard to be used with the conditional variants of locks, like
+ *	down_read_trylock() or mutex_lock_interruptible. 'fail' are one or more
+ *	statements that are executed when waiting for a lock is interrupted or
+ *	when a _trylock() fails in case of contention.
+ *
+ *	Example:
+ *
+ *		cond_guard(rwsem_read_try, { printk(...); return 0; }, &semaphore);
+ *
  * scoped_guard (name, args...) { }:
  *	similar to CLASS(name, scope)(args), except the variable (with the
  *	explicit name 'scope') is declard in a for-loop such that its scope is
@@ -165,6 +175,10 @@ static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \
 
 #define __guard_ptr(_name) class_##_name##_lock_ptr
 
+#define cond_guard(_name, _fail, args...) \
+	CLASS(_name, scope)(args); \
+	if (!__guard_ptr(_name)(&scope)) _fail
+
 #define scoped_guard(_name, args...)					\
 	for (CLASS(_name, scope)(args),					\
 	     *done = NULL; __guard_ptr(_name)(&scope) && !done; done = (void *)1)
-- 
2.43.0