Commit 473e470f authored Feb 03, 2026 by Arnd Bergmann Committed by Steven Rostedt (Google) Mar 23, 2026

tracing: move printf() attribute on ftrace_vbprintk()

The sunrpc change to use trace_printk() for debugging caused
a new warning for every instance of dprintk() in some configurations,
when -Wformat-security is enabled:

fs/nfs/getroot.c: In function 'nfs_get_root':
fs/nfs/getroot.c:90:17: error: format not a string literal and no format arguments [-Werror=format-security]
   90 |                 nfs_errorf(fc, "NFS: Couldn't getattr on root");

I've been slowly chipping away at those warnings over time with the
intention of enabling them by default in the future. While I could not
figure out why this only happens for this one instance, I see that the
__trace_bprintk() function is always called with a local variable as
the format string, rather than a literal.

Move the __printf(2,3) annotation on this function from the declaration
to the caller. As this is can only be validated for literals, the
attribute on the declaration causes the warnings every time, but
removing it entirely introduces a new warning on the __ftrace_vbprintk()
definition.

The format strings still get checked because the underlying literal keeps
getting passed into __trace_printk() in the "else" branch, which is not
taken but still evaluated for compile-time warnings.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Anna Schumaker <anna.schumaker@oracle.com>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Simon Horman <horms@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Yury Norov <ynorov@nvidia.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Link: https://patch.msgid.link/20260203164545.3174910-1-arnd@kernel.org


Fixes: ec7d8e68 ("sunrpc: add a Kconfig option to redirect dfprintk() output to trace buffer")
Acked-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

parent c3692998

include/linux/trace_printk.h

+0 −1

Original line number	Diff line number	Diff line
		@@ -107,7 +107,6 @@ do { \
		__trace_printk(_THIS_IP_, fmt, ##args); \
		} while (0)

		extern __printf(2, 3)
		int __trace_bprintk(unsigned long ip, const char *fmt, ...);

		extern __printf(2, 3)

kernel/trace/trace_printk.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -197,6 +197,7 @@ struct notifier_block module_trace_bprintk_format_nb = {
		.notifier_call = module_trace_bprintk_format_notify,
		};

		__printf(2, 3)
		int __trace_bprintk(unsigned long ip, const char *fmt, ...)
		{
		int ret;