[RFC PATCH v2] cleanup: Add cond_guard() to conditional guards

[Fabio M. De Francesco]

Add cond_guard() to conditional guards.

cond_guard() is used for the _interruptible(), _killable(), and _try
versions of locks. It expects a block where the failure can be handled
(e.g., calling printk() and returning -EINTR in case of failure).

As the other guards, it avoids to open code the release of the lock
after a goto to an 'out' label.

This remains an RFC because Dan suggested a slightly different syntax:

	if (cond_guard(...))
		return -EINTR;

But the scoped_cond_guard() macro omits the if statement:

    	scoped_cond_guard (...) {
    	}

Thus define cond_guard() similarly to scoped_cond_guard() but with a block
to handle the failure case:

	cond_guard(...)
		return -EINTR;

Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: 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>
---
 drivers/cxl/core/region.c | 17 +++++------------
 include/linux/cleanup.h   | 13 +++++++++++++
 2 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index 0f05692bfec3..20d405f01df5 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -666,28 +666,21 @@ static size_t show_targetN(struct cxl_region *cxlr, char *buf, int pos)
 {
 	struct cxl_region_params *p = &cxlr->params;
 	struct cxl_endpoint_decoder *cxled;
-	int rc;
 
-	rc = down_read_interruptible(&cxl_region_rwsem);
-	if (rc)
-		return rc;
+	cond_guard(rwsem_read_intr, &cxl_region_rwsem)
+		return -EINTR;
 
 	if (pos >= p->interleave_ways) {
 		dev_dbg(&cxlr->dev, "position %d out of range %d\n", pos,
 			p->interleave_ways);
-		rc = -ENXIO;
-		goto out;
+		return -ENXIO;
 	}
 
 	cxled = p->targets[pos];
 	if (!cxled)
-		rc = sysfs_emit(buf, "\n");
+		return sysfs_emit(buf, "\n");
 	else
-		rc = sysfs_emit(buf, "%s\n", dev_name(&cxled->cxld.dev));
-out:
-	up_read(&cxl_region_rwsem);
-
-	return rc;
+		return sysfs_emit(buf, "%s\n", dev_name(&cxled->cxld.dev));
 }
 
 static int match_free_decoder(struct device *dev, void *data)
diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h
index c2d09bc4f976..fc850e61a47e 100644
--- a/include/linux/cleanup.h
+++ b/include/linux/cleanup.h
@@ -134,6 +134,15 @@ 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, args...):
+ * 	for conditional locks like mutex_trylock() or down_read_interruptible().
+ * 	It expects a block for handling errors like in the following example:
+ *
+ * 	cond_guard(rwsem_read_intr, &my_sem) {
+ * 		printk(KERN_NOTICE "Try failure in work0()\n");
+ * 		return -EINTR;
+ * 	}
+ *
  * 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 +174,10 @@ static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \
 
 #define __guard_ptr(_name) class_##_name##_lock_ptr
 
+#define cond_guard(_name, args...) \
+	CLASS(_name, scope)(args); \
+	if (!__guard_ptr(_name)(&scope))
+
 #define scoped_guard(_name, args...)					\
 	for (CLASS(_name, scope)(args),					\
 	     *done = NULL; __guard_ptr(_name)(&scope) && !done; done = (void *)1)
-- 
2.43.0