linux-kernel - [RFC][PATCH 3/5] refcount: Improve out-of-line code-gen

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Message-ID: <20211208183906.548393311@infradead.org>
Date:   Wed, 08 Dec 2021 19:36:58 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     will@...nel.org, boqun.feng@...il.com
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, peterz@...radead.org,
        mark.rutland@....com, elver@...gle.com, keescook@...omium.org,
        hch@...radead.org, torvalds@...ux-foundation.org
Subject: [RFC][PATCH 3/5] refcount: Improve out-of-line code-gen

Allow a number of ops to tail-call refcount_warn_saturate() in order
to generate smaller out-of-line code.

   text    data     bss     dec     hex filename
  97341    4985    1116  103442   19412 defconfig-build/kernel/events/core.o
  97299    4985    1116  103400   193e8 defconfig-build/kernel/events/core.o

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 include/linux/refcount.h |    9 ++++-----
 lib/refcount.c           |    4 +++-
 2 files changed, 7 insertions(+), 6 deletions(-)

--- a/include/linux/refcount.h
+++ b/include/linux/refcount.h
@@ -124,7 +124,7 @@ enum refcount_saturation_type {
 	REFCOUNT_DEC_LEAK,
 };
 
-void refcount_warn_saturate(refcount_t *r, enum refcount_saturation_type t);
+bool refcount_warn_saturate(refcount_t *r, enum refcount_saturation_type t);
 
 /**
  * refcount_set - set a refcount's value
@@ -160,7 +160,7 @@ static inline __must_check bool __refcou
 		*oldp = old;
 
 	if (unlikely(old < 0 || old + i < 0))
-		refcount_warn_saturate(r, REFCOUNT_ADD_NOT_ZERO_OVF);
+		return refcount_warn_saturate(r, REFCOUNT_ADD_NOT_ZERO_OVF);
 
 	return old;
 }
@@ -283,7 +283,7 @@ static inline __must_check bool __refcou
 	}
 
 	if (unlikely(old < 0 || old - i < 0))
-		refcount_warn_saturate(r, REFCOUNT_SUB_UAF);
+		return refcount_warn_saturate(r, REFCOUNT_SUB_UAF);
 
 	return false;
 }
@@ -335,8 +335,7 @@ static inline __must_check bool refcount
 {
 	return atomic_dec_and_test_ofl(&r->refs, Eoverflow);
 Eoverflow:
-	refcount_warn_saturate(r, REFCOUNT_SUB_UAF);
-	return false;
+	return refcount_warn_saturate(r, REFCOUNT_SUB_UAF);
 }
 
 static inline void __refcount_dec(refcount_t *r, int *oldp)
--- a/lib/refcount.c
+++ b/lib/refcount.c
@@ -10,7 +10,7 @@
 
 #define REFCOUNT_WARN(str)	WARN_ONCE(1, "refcount_t: " str ".\n")
 
-void refcount_warn_saturate(refcount_t *r, enum refcount_saturation_type t)
+bool refcount_warn_saturate(refcount_t *r, enum refcount_saturation_type t)
 {
 	int old = refcount_read(r);
 	refcount_set(r, REFCOUNT_SATURATED);
@@ -38,6 +38,8 @@ void refcount_warn_saturate(refcount_t *
 	default:
 		REFCOUNT_WARN("unknown saturation event!?");
 	}
+
+	return false;
 }
 EXPORT_SYMBOL(refcount_warn_saturate);