[1/3] cleanup: Add cond_guard() to conditional guards
Commit Message
From: Fabio M. De Francesco <fabio.maria.de.francesco@linux.intel.com>
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 statement-expression) that is passed as its
second argument. That statement (or statement-expression) is executed if
waiting for a lock is interrupted or if a _trylock() fails in case of
contention.
Usage example:
cond_guard(mutex_intr, return -EINTR, &mutex);
Consistent with other usage of _guard(), locks are unlocked at the exit of
the scope where cond_guard() is called. This macro can be called multiple
times in the same scope.
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Suggested-by: Dan Williams <dan.j.williams@intel.com>
Suggested-by: Ira Weiny <ira.weiny@intel.com>
Suggested-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Fabio M. De Francesco <fabio.maria.de.francesco@linux.intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
include/linux/cleanup.h | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
Comments
On Tue, 27 Feb 2024 at 08:48, Dan Williams <dan.j.williams@intel.com> wrote:
>
> cond_guard(mutex_intr, return -EINTR, &mutex);
Again, this is *not* helping make code readable and less likely to have bugs.
The macro has obvious deficiencies, like the "_fail" argument not
being surrounded by "{ }" (the equivalent of parenthesizing an
expression argument), but even with that trivial fix the syntax is
just too ugly to live, and doesn't match normal C syntax.
And yes, we have other macros that don't have normal C syntax, and
they are ugly too (example: #define CHKINFO(ret) in
drivers/video/fbdev/hgafb.c), but we should have higher standards for
globally visible helpers, and we should have *MUCH* higher standards
for helpers that are supposed to be all about reducing mistakes.
Bad / odd syntax does not reduce mistakes.
If a sane 'guard' model doesn't work for some code, the answer is not
to make an insane guard model. The answer is to not use 'guard' in
code like that.
Linus
@@ -134,6 +134,19 @@ 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' is a
+ * statement or statement-expression that is executed if waiting for a
+ * lock is interrupted or if a _trylock() fails in case of contention.
+ *
+ * Example:
+ *
+ * cond_guard(mutex_intr, return -EINTR, &mutex);
+ *
+ * This macro can be called multiple times in the same scope, for it
+ * declares unique instances of type 'name'.
+ *
* 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 +178,13 @@ static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \
#define __guard_ptr(_name) class_##_name##_lock_ptr
+#define __cond_guard(__unique, _name, _fail, args...) \
+ CLASS(_name, __unique)(args); \
+ if (!__guard_ptr(_name)(&__unique)) _fail; \
+ else { }
+#define cond_guard(_name, _fail, args...) \
+ __cond_guard(__UNIQUE_ID(scope), _name, _fail, args)
+
#define scoped_guard(_name, args...) \
for (CLASS(_name, scope)(args), \
*done = NULL; __guard_ptr(_name)(&scope) && !done; done = (void *)1)