linux-kernel - [PATCH 1/7] closures: Improve closure_put_after_sub

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Message-ID: <20251004020049.918665-2-kent.overstreet@linux.dev>
Date: Fri,  3 Oct 2025 22:00:43 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: linux-kernel@...r.kernel.org
Cc: akpm@...ux-foundation.org,
	Kent Overstreet <kent.overstreet@...ux.dev>
Subject: [PATCH 1/7] closures: Improve closure_put_after_sub_checks

Add a guard bit for CLOSURE_DESTRUCTOR underflow, print the full
cl->remaining value, and rename variables for clarity.

Signed-off-by: Kent Overstreet <kent.overstreet@...ux.dev>
---
 include/linux/closure.h |  2 +-
 lib/closure.c           | 28 +++++++++++++++-------------
 2 files changed, 16 insertions(+), 14 deletions(-)

diff --git a/include/linux/closure.h b/include/linux/closure.h
index 880fe85e35e9..a6fcc33fafce 100644
--- a/include/linux/closure.h
+++ b/include/linux/closure.h
@@ -135,7 +135,7 @@ enum closure_state {
 };
 
 #define CLOSURE_GUARD_MASK					\
-	((CLOSURE_DESTRUCTOR|CLOSURE_WAITING|CLOSURE_RUNNING) << 1)
+	(((CLOSURE_DESTRUCTOR|CLOSURE_WAITING|CLOSURE_RUNNING) << 1)|(CLOSURE_BITS_START >> 1))
 
 #define CLOSURE_REMAINING_MASK		(CLOSURE_BITS_START - 1)
 #define CLOSURE_REMAINING_INITIALIZER	(1|CLOSURE_RUNNING)
diff --git a/lib/closure.c b/lib/closure.c
index 2bfe7d2a0048..5fafc8b0e99d 100644
--- a/lib/closure.c
+++ b/lib/closure.c
@@ -13,23 +13,25 @@
 #include <linux/seq_file.h>
 #include <linux/sched/debug.h>
 
-static inline void closure_put_after_sub_checks(int flags)
+static void closure_val_checks(struct closure *cl, unsigned new)
 {
-	int r = flags & CLOSURE_REMAINING_MASK;
-
-	if (WARN(flags & CLOSURE_GUARD_MASK,
-		 "closure has guard bits set: %x (%u)",
-		 flags & CLOSURE_GUARD_MASK, (unsigned) __fls(r)))
-		r &= ~CLOSURE_GUARD_MASK;
-
-	WARN(!r && (flags & ~CLOSURE_DESTRUCTOR),
-	     "closure ref hit 0 with incorrect flags set: %x (%u)",
-	     flags & ~CLOSURE_DESTRUCTOR, (unsigned) __fls(flags));
+	unsigned count = new & CLOSURE_REMAINING_MASK;
+
+	if (WARN(new & CLOSURE_GUARD_MASK,
+		 "closure %ps has guard bits set: %x (%u)",
+		 cl->fn,
+		 new, (unsigned) __fls(new & CLOSURE_GUARD_MASK)))
+		new &= ~CLOSURE_GUARD_MASK;
+
+	WARN(!count && (new & ~CLOSURE_DESTRUCTOR),
+	     "closure %ps ref hit 0 with incorrect flags set: %x (%u)",
+	     cl->fn,
+	     new, (unsigned) __fls(new));
 }
 
 static inline void closure_put_after_sub(struct closure *cl, int flags)
 {
-	closure_put_after_sub_checks(flags);
+	closure_val_checks(cl, flags);
 
 	if (!(flags & CLOSURE_REMAINING_MASK)) {
 		smp_acquire__after_ctrl_dep();
@@ -167,7 +169,7 @@ void __sched closure_return_sync(struct closure *cl)
 	unsigned flags = atomic_sub_return_release(1 + CLOSURE_RUNNING - CLOSURE_DESTRUCTOR,
 						   &cl->remaining);
 
-	closure_put_after_sub_checks(flags);
+	closure_val_checks(cl, flags);
 
 	if (unlikely(flags & CLOSURE_REMAINING_MASK)) {
 		while (1) {
-- 
2.51.0