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Subject[PATCH net-next v3 1/2] once: implement DO_ONCE_LITE for non-fast-path "do once" functionality
Date
From: Tanner Love <tannerlove@google.com>

Certain uses of "do once" functionality reside outside of fast path,
and so do not require jump label patching via static keys, making
existing DO_ONCE undesirable in such cases.

Replace uses of __section(".data.once") with DO_ONCE_LITE(_IF)?

This patch changes the return values of xfs_printk_once, printk_once,
and printk_deferred_once. Before, they returned whether the print was
performed, but now, they always return true. This is okay because the
return values of the following macros are entirely ignored throughout
the kernel:
- xfs_printk_once
- xfs_warn_once
- xfs_notice_once
- xfs_info_once
- printk_once
- pr_emerg_once
- pr_alert_once
- pr_crit_once
- pr_err_once
- pr_warn_once
- pr_notice_once
- pr_info_once
- pr_devel_once
- pr_debug_once
- printk_deferred_once
- orc_warn

Changes
v3:
- Expand commit message to explain why changing return values of
xfs_printk_once, printk_once, printk_deferred_once is benign
v2:
- Fix i386 build warnings

Signed-off-by: Tanner Love <tannerlove@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Acked-by: Mahesh Bandewar <maheshb@google.com>
---
fs/xfs/xfs_message.h | 13 +++----------
include/asm-generic/bug.h | 37 +++++++------------------------------
include/linux/once_lite.h | 24 ++++++++++++++++++++++++
include/linux/printk.h | 23 +++--------------------
kernel/trace/trace.h | 13 +++----------
5 files changed, 40 insertions(+), 70 deletions(-)
create mode 100644 include/linux/once_lite.h

diff --git a/fs/xfs/xfs_message.h b/fs/xfs/xfs_message.h
index 7ec1a9207517..bb9860ec9a93 100644
--- a/fs/xfs/xfs_message.h
+++ b/fs/xfs/xfs_message.h
@@ -2,6 +2,8 @@
#ifndef __XFS_MESSAGE_H
#define __XFS_MESSAGE_H 1

+#include <linux/once_lite.h>
+
struct xfs_mount;

extern __printf(2, 3)
@@ -41,16 +43,7 @@ do { \
} while (0)

#define xfs_printk_once(func, dev, fmt, ...) \
-({ \
- static bool __section(".data.once") __print_once; \
- bool __ret_print_once = !__print_once; \
- \
- if (!__print_once) { \
- __print_once = true; \
- func(dev, fmt, ##__VA_ARGS__); \
- } \
- unlikely(__ret_print_once); \
-})
+ DO_ONCE_LITE(func, dev, fmt, ##__VA_ARGS__)

#define xfs_emerg_ratelimited(dev, fmt, ...) \
xfs_printk_ratelimited(xfs_emerg, dev, fmt, ##__VA_ARGS__)
diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index b402494883b6..bafc51f483c4 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -4,6 +4,7 @@

#include <linux/compiler.h>
#include <linux/instrumentation.h>
+#include <linux/once_lite.h>

#define CUT_HERE "------------[ cut here ]------------\n"

@@ -140,39 +141,15 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
})

#ifndef WARN_ON_ONCE
-#define WARN_ON_ONCE(condition) ({ \
- static bool __section(".data.once") __warned; \
- int __ret_warn_once = !!(condition); \
- \
- if (unlikely(__ret_warn_once && !__warned)) { \
- __warned = true; \
- WARN_ON(1); \
- } \
- unlikely(__ret_warn_once); \
-})
+#define WARN_ON_ONCE(condition) \
+ DO_ONCE_LITE_IF(condition, WARN_ON, 1)
#endif

-#define WARN_ONCE(condition, format...) ({ \
- static bool __section(".data.once") __warned; \
- int __ret_warn_once = !!(condition); \
- \
- if (unlikely(__ret_warn_once && !__warned)) { \
- __warned = true; \
- WARN(1, format); \
- } \
- unlikely(__ret_warn_once); \
-})
+#define WARN_ONCE(condition, format...) \
+ DO_ONCE_LITE_IF(condition, WARN, 1, format)

-#define WARN_TAINT_ONCE(condition, taint, format...) ({ \
- static bool __section(".data.once") __warned; \
- int __ret_warn_once = !!(condition); \
- \
- if (unlikely(__ret_warn_once && !__warned)) { \
- __warned = true; \
- WARN_TAINT(1, taint, format); \
- } \
- unlikely(__ret_warn_once); \
-})
+#define WARN_TAINT_ONCE(condition, taint, format...) \
+ DO_ONCE_LITE_IF(condition, WARN_TAINT, 1, taint, format)

#else /* !CONFIG_BUG */
#ifndef HAVE_ARCH_BUG
diff --git a/include/linux/once_lite.h b/include/linux/once_lite.h
new file mode 100644
index 000000000000..861e606b820f
--- /dev/null
+++ b/include/linux/once_lite.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_ONCE_LITE_H
+#define _LINUX_ONCE_LITE_H
+
+#include <linux/types.h>
+
+/* Call a function once. Similar to DO_ONCE(), but does not use jump label
+ * patching via static keys.
+ */
+#define DO_ONCE_LITE(func, ...) \
+ DO_ONCE_LITE_IF(true, func, ##__VA_ARGS__)
+#define DO_ONCE_LITE_IF(condition, func, ...) \
+ ({ \
+ static bool __section(".data.once") __already_done; \
+ bool __ret_do_once = !!(condition); \
+ \
+ if (unlikely(__ret_do_once && !__already_done)) { \
+ __already_done = true; \
+ func(__VA_ARGS__); \
+ } \
+ unlikely(__ret_do_once); \
+ })
+
+#endif /* _LINUX_ONCE_LITE_H */
diff --git a/include/linux/printk.h b/include/linux/printk.h
index fe7eb2351610..885379a1c9a1 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -8,6 +8,7 @@
#include <linux/linkage.h>
#include <linux/cache.h>
#include <linux/ratelimit_types.h>
+#include <linux/once_lite.h>

extern const char linux_banner[];
extern const char linux_proc_banner[];
@@ -436,27 +437,9 @@ extern int kptr_restrict;

#ifdef CONFIG_PRINTK
#define printk_once(fmt, ...) \
-({ \
- static bool __section(".data.once") __print_once; \
- bool __ret_print_once = !__print_once; \
- \
- if (!__print_once) { \
- __print_once = true; \
- printk(fmt, ##__VA_ARGS__); \
- } \
- unlikely(__ret_print_once); \
-})
+ DO_ONCE_LITE(printk, fmt, ##__VA_ARGS__)
#define printk_deferred_once(fmt, ...) \
-({ \
- static bool __section(".data.once") __print_once; \
- bool __ret_print_once = !__print_once; \
- \
- if (!__print_once) { \
- __print_once = true; \
- printk_deferred(fmt, ##__VA_ARGS__); \
- } \
- unlikely(__ret_print_once); \
-})
+ DO_ONCE_LITE(printk_deferred, fmt, ##__VA_ARGS__)
#else
#define printk_once(fmt, ...) \
no_printk(fmt, ##__VA_ARGS__)
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index cd80d046c7a5..d5d8c088a55d 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -20,6 +20,7 @@
#include <linux/irq_work.h>
#include <linux/workqueue.h>
#include <linux/ctype.h>
+#include <linux/once_lite.h>

#ifdef CONFIG_FTRACE_SYSCALLS
#include <asm/unistd.h> /* For NR_SYSCALLS */
@@ -99,16 +100,8 @@ enum trace_type {
#include "trace_entries.h"

/* Use this for memory failure errors */
-#define MEM_FAIL(condition, fmt, ...) ({ \
- static bool __section(".data.once") __warned; \
- int __ret_warn_once = !!(condition); \
- \
- if (unlikely(__ret_warn_once && !__warned)) { \
- __warned = true; \
- pr_err("ERROR: " fmt, ##__VA_ARGS__); \
- } \
- unlikely(__ret_warn_once); \
-})
+#define MEM_FAIL(condition, fmt, ...) \
+ DO_ONCE_LITE_IF(condition, pr_err, "ERROR: " fmt, ##__VA_ARGS__)

/*
* syscalls are special, and need special handling, this is why
--
2.32.0.93.g670b81a890-goog
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