[PATCH v13 38/39] printk.h: fix overzealous pr_fmt in pr_debug_ratelimited
From: Jim Cromie via B4 Relay
Date: Tue Oct 27 2026 - 16:30:55 EST
From: Jim Cromie <jim.cromie@xxxxxxxxx>
Historically, the CONFIG_DYNAMIC_DEBUG implementation of
pr_debug_ratelimited() passed raw fmt to both metadata and runtime:
DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, fmt);
if (unlikely(...) && __ratelimit(&_rs))
__dynamic_pr_debug(&descriptor, fmt, ##__VA_ARGS__);
While descriptor metadata was clean, emitted dmesg records lacked the
pr_fmt prefix present in the !CONFIG_DYNAMIC_DEBUG fallbacks.
In 2015, commit 515a9adce0f0 ("include/linux/printk.h: include pr_fmt
in pr_debug_ratelimited") fixed the missing prefix by wrapping the fmt
arg in __dynamic_pr_debug() with pr_fmt(). However, it also wrapped
the fmt arg in the METADATA macro:
DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, pr_fmt(fmt));
This would break if the following were true:
0. CONFIG_DYNAMIC_DEBUG=y
1. #define pr_fmt(fmt) KBUILD_MODNAME ".%s " fmt, __func__
2. a pr_debug_ratelimited() call.
Philipp Hahn recently encountered this, reported the build failure,
added a test case to test_dynamic_debug.c, and proposed adding
variadic arguments (", ...") to DEFINE_DYNAMIC_DEBUG_METADATA_CLS to
slurp the trailing arguments. This approach had 2 flaws:
1. the __func__ is not a preprocessor macro
2. adding the prefix to the .format would break anchored queries:
echo format "^foo" > /proc/dynamic_debug/control
So modify the DEFINE_DYNAMIC_DEBUG_METADATA() call in
pr_debug_ratelimited, dropping the pr_fmt() wrapper on the fmt arg.
This restores consistency with all the other dyndbg callers:
dynamic_pr_debug, dev_dbg_ratelimited, net_dbg_ratelimited.
Reported-by: Philipp Hahn <phahn-oss@xxxxxx>
Fixes: 515a9adce0f0 ("include/linux/printk.h: include pr_fmt in pr_debug_ratelimited")
cc: Jason A. Donenfeld <Jason@xxxxxxxxx>
cc: Petr Mladek <pmladek@xxxxxxxx>
Signed-off-by: Jim Cromie <jim.cromie@xxxxxxxxx>
---
v13:
. pass raw fmt to DEFINE_DYNAMIC_DEBUG_METADATA in pr_debug_ratelimited(),
restoring pre-515a9adce0f0 behavior.
. drop vestigial '...' from DEFINE_DYNAMIC_DEBUG_METADATA_CLS as noted by
Petr Mladek, leaving include/linux/dynamic_debug.h untouched.
. rewrite commit description chronologically and attribute Philipp Hahn
with Reported-by.
v11:
. update golden record hashes for FT_modprobe_w_param tests after
comma-token and native classmap attachment fixes.
v10:
. pass raw fmt to DEFINE_DYNAMIC_DEBUG_METADATA in pr_debug_ratelimited().
---
include/linux/printk.h | 2 +-
lib/test_dynamic_debug.c | 4 ++--
.../selftests/dynamic_debug/dyndbg_selftest.sh | 26 +++++++++++-----------
3 files changed, 16 insertions(+), 16 deletions(-)
diff --git a/include/linux/printk.h b/include/linux/printk.h
index f594c1266bfd..5d701952e739 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -742,7 +742,7 @@ do { \
static DEFINE_RATELIMIT_STATE(_rs, \
DEFAULT_RATELIMIT_INTERVAL, \
DEFAULT_RATELIMIT_BURST); \
- DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, pr_fmt(fmt)); \
+ DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, fmt); \
if (DYNAMIC_DEBUG_BRANCH(descriptor) && \
__ratelimit(&_rs)) \
__dynamic_pr_debug(&descriptor, pr_fmt(fmt), ##__VA_ARGS__); \
diff --git a/lib/test_dynamic_debug.c b/lib/test_dynamic_debug.c
index 2f19ecb1f295..965f3a6919c0 100644
--- a/lib/test_dynamic_debug.c
+++ b/lib/test_dynamic_debug.c
@@ -23,7 +23,7 @@
* the usage clearer.
*/
#if defined(TEST_DYNAMIC_DEBUG_SUBMOD)
- #define pr_fmt(fmt) "test_dd_submod: " fmt
+ #define pr_fmt(fmt) "test_dd_submod: %s " fmt, __func__
#else
#define pr_fmt(fmt) "test_dd: " fmt
#endif
@@ -326,7 +326,7 @@ static int __init test_dynamic_debug_init(void)
static void __exit test_dynamic_debug_exit(void)
{
- pr_debug("exited\n");
+ pr_debug_ratelimited("exited\n");
}
module_init(test_dynamic_debug_init);
diff --git a/tools/testing/selftests/dynamic_debug/dyndbg_selftest.sh b/tools/testing/selftests/dynamic_debug/dyndbg_selftest.sh
index fd9a3dff4099..2bdfdb3876ee 100755
--- a/tools/testing/selftests/dynamic_debug/dyndbg_selftest.sh
+++ b/tools/testing/selftests/dynamic_debug/dyndbg_selftest.sh
@@ -724,40 +724,40 @@ function GOLDEN_RECORDS {
#K= e11c22649735cedb6c30321378100e11 FT_classmap_inheritance.2
#K= 5d0f3701517aa3a461c8887c332bdb42 FT_classmap_inheritance.3
#K= d39188ded831453d90d77390546b314d FT_classmap_inheritance.4
-#K= f43e0aff8a4b38435b73d90ed8100d1b FT_classmap_inheritance.5
+#K= 62b6803edf43519186d6185bebf34352 FT_classmap_inheritance.5
#K= d2e8b8c5a5b4e7b9bbe1a29460a3c07d FT_modprobe_w_param.1
#K= d2e8b8c5a5b4e7b9bbe1a29460a3c07d FT_modprobe_w_param.2
-#K= 11032ef17569bd151c3806527a2428be FT_modprobe_w_param.3
+#K= 20d8a1fac0330f1b5cc582ce93792d58 FT_modprobe_w_param.3
#K= 0239d8c0808eef396782362613f675b0 FT_modprobe_w_param.4
-#K= 942e62ca24809cad666c5725aeb14376 FT_modprobe_w_param.5
+#K= 3c19dd83b330a9d59901281aaa3bacf8 FT_modprobe_w_param.5
#K= 0239d8c0808eef396782362613f675b0 FT_modprobe_w_param.6
-#K= fe1aadca4b2b4165d8d5c98e973f9e4b FT_modprobe_w_param.7
+#K= 86b7a18d7a692187aa0b7cc0b6886e77 FT_modprobe_w_param.7
#K= 0239d8c0808eef396782362613f675b0 FT_modprobe_w_param.8
#K= 535ab526b24a7214de41d92e94bbd52c FT_modprobe_w_param.9
#K= 0239d8c0808eef396782362613f675b0 FT_modprobe_w_param.10
-#K= 7c02282dcfb73eb5ffb9629ce63360e5 FT_modprobe_w_param.11
+#K= 64f91218760ca86d28a4b9b2d23849fb FT_modprobe_w_param.11
#K= 0239d8c0808eef396782362613f675b0 FT_modprobe_w_param.12
-#K= b0942decc84dae237019bc2877ff02e7 FT_modprobe_w_param.13
+#K= 03bad8f76b3587c2e8bdb9df43110a5e FT_modprobe_w_param.13
#K= 0239d8c0808eef396782362613f675b0 FT_modprobe_w_param.14
-#K= efe8e3b8080c3310708b7505d60f7703 FT_modprobe_w_param.15
+#K= 04b59fe2db45bc6bb314e9102b92dd64 FT_modprobe_w_param.15
#K= 0239d8c0808eef396782362613f675b0 FT_modprobe_w_param.16
#K= d682c98ced7d31f1555ab474a9ebe253 FT_modprobe_w_param.17
#K= 0239d8c0808eef396782362613f675b0 FT_modprobe_w_param.18
#K= c468e49e8ce1f1aa25a3c6684f221fe5 FT_modprobe_w_param.19
#K= c468e49e8ce1f1aa25a3c6684f221fe5 FT_modprobe_w_param.20
-#K= ef2408a036206c895d95061521f67906 FT_modprobe_w_param.21
+#K= 2b31c44bc2eb5b5d666dc1887c38b8dd FT_modprobe_w_param.21
#K= 0239d8c0808eef396782362613f675b0 FT_modprobe_w_param.22
-#K= 92c0174d5de412de82e3d5837b0690d0 FT_modprobe_w_param.23
+#K= 3bba1f526e669807407d9be380117564 FT_modprobe_w_param.23
#K= 0239d8c0808eef396782362613f675b0 FT_modprobe_w_param.24
-#K= a563a79aeffbf3d8cf2e37ab93898ae9 FT_modprobe_w_param.25
+#K= 1dc9fbf8e7ce91929308a441e3707915 FT_modprobe_w_param.25
#K= 0239d8c0808eef396782362613f675b0 FT_modprobe_w_param.26
#K= 8d2f4db3b7885064a56594e1d81deb26 FT_modprobe_w_param.27
#K= 0239d8c0808eef396782362613f675b0 FT_modprobe_w_param.28
-#K= 05e8884875609af295ec71a7acf33c60 FT_modprobe_w_param.29
+#K= 0658c273db527fb4fcaadbb142bf0565 FT_modprobe_w_param.29
#K= 0239d8c0808eef396782362613f675b0 FT_modprobe_w_param.30
-#K= c70f769b4c9cc905d23d6b3e5ac432c8 FT_modprobe_w_param.31
+#K= 20cac1fd02b4615b337e84aa87892afc FT_modprobe_w_param.31
#K= 0239d8c0808eef396782362613f675b0 FT_modprobe_w_param.32
-#K= 72bf5368385d19e7843cf268d1bac7f9 FT_modprobe_w_param.33
+#K= 8eb7924c66978d844e97bee9f91b981e FT_modprobe_w_param.33
#K= 0239d8c0808eef396782362613f675b0 FT_modprobe_w_param.34
#K= 28ace93a95da7aaea5b9b54a8656a2cf FT_modprobe_w_param.35
#K= 0239d8c0808eef396782362613f675b0 FT_modprobe_w_param.36
--
2.56.0