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From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     rcu@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, kernel-team@meta.com,
        rostedt@goodmis.org, "Uladzislau Rezki (Sony)" <urezki@gmail.com>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Joel Fernandes <joel@joelfernandes.org>
Subject: [PATCH rcu 1/8] rcu/kvfree: Eliminate k[v]free_rcu() single argument macro
Date:   Wed, 10 May 2023 10:02:35 -0700
Message-Id: <20230510170242.2187714-1-paulmck@kernel.org>
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From: "Uladzislau Rezki (Sony)" <urezki@gmail.com>

The kvfree_rcu() and kfree_rcu() APIs are hazardous in that if you forget
the second argument, it works, but might sleep.  This sleeping can be a
correctness bug from atomic contexts, and even in non-atomic contexts it
might introduce unacceptable latencies.  This commit therefore removes the
single-argument kvfree_rcu() and kfree_rcu() macros.  Code that would have
previously used these single-argument kvfree_rcu() and kfree_rcu() macros
should instead use kvfree_rcu_mightsleep() or kfree_rcu_mightsleep().

[ paulmck: Apply Joel Fernandes feedback. ]

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 include/linux/rcupdate.h | 29 ++++++++---------------------
 1 file changed, 8 insertions(+), 21 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index dcd2cf1e8326..744869ef930a 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -957,9 +957,8 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
 
 /**
  * kfree_rcu() - kfree an object after a grace period.
- * @ptr: pointer to kfree for both single- and double-argument invocations.
- * @rhf: the name of the struct rcu_head within the type of @ptr,
- *       but only for double-argument invocations.
+ * @ptr: pointer to kfree for double-argument invocations.
+ * @rhf: the name of the struct rcu_head within the type of @ptr.
  *
  * Many rcu callbacks functions just call kfree() on the base structure.
  * These functions are trivial, but their size adds up, and furthermore
@@ -984,26 +983,18 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
  * The BUILD_BUG_ON check must not involve any function calls, hence the
  * checks are done in macros here.
  */
-#define kfree_rcu(ptr, rhf...) kvfree_rcu(ptr, ## rhf)
+#define kfree_rcu(ptr, rhf) kvfree_rcu_arg_2(ptr, rhf)
+#define kvfree_rcu(ptr, rhf) kvfree_rcu_arg_2(ptr, rhf)
 
 /**
- * kvfree_rcu() - kvfree an object after a grace period.
- *
- * This macro consists of one or two arguments and it is
- * based on whether an object is head-less or not. If it
- * has a head then a semantic stays the same as it used
- * to be before:
- *
- *     kvfree_rcu(ptr, rhf);
- *
- * where @ptr is a pointer to kvfree(), @rhf is the name
- * of the rcu_head structure within the type of @ptr.
+ * kfree_rcu_mightsleep() - kfree an object after a grace period.
+ * @ptr: pointer to kfree for single-argument invocations.
  *
  * When it comes to head-less variant, only one argument
  * is passed and that is just a pointer which has to be
  * freed after a grace period. Therefore the semantic is
  *
- *     kvfree_rcu(ptr);
+ *     kfree_rcu_mightsleep(ptr);
  *
  * where @ptr is the pointer to be freed by kvfree().
  *
@@ -1012,13 +1003,9 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
  * annotation. Otherwise, please switch and embed the
  * rcu_head structure within the type of @ptr.
  */
-#define kvfree_rcu(...) KVFREE_GET_MACRO(__VA_ARGS__,		\
-	kvfree_rcu_arg_2, kvfree_rcu_arg_1)(__VA_ARGS__)
-
+#define kfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr)
 #define kvfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr)
-#define kfree_rcu_mightsleep(ptr) kvfree_rcu_mightsleep(ptr)
 
-#define KVFREE_GET_MACRO(_1, _2, NAME, ...) NAME
 #define kvfree_rcu_arg_2(ptr, rhf)					\
 do {									\
 	typeof (ptr) ___p = (ptr);					\
-- 
2.40.1