linux-kernel - [PATCH 2/2] sunrpc: add a Kconfig option to redirect dfprintk() output to trace buffer

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Message-Id: <20250821-nfs-testing-v1-2-f06099963eda@kernel.org>
Date: Thu, 21 Aug 2025 13:16:54 -0400
From: Jeff Layton <jlayton@...nel.org>
To: Trond Myklebust <trondmy@...nel.org>, Anna Schumaker <anna@...nel.org>, 
 Chuck Lever <chuck.lever@...cle.com>, NeilBrown <neil@...wn.name>, 
 Olga Kornievskaia <okorniev@...hat.com>, Dai Ngo <Dai.Ngo@...cle.com>, 
 Tom Talpey <tom@...pey.com>, "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>
Cc: linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org, 
 netdev@...r.kernel.org, Jeff Layton <jlayton@...nel.org>
Subject: [PATCH 2/2] sunrpc: add a Kconfig option to redirect dfprintk()
 output to trace buffer

We have a lot of old dprintk() call sites that aren't going anywhere
anytime soon. At the same time, turning them up is a serious burden on
the host due to the console locking overhead.

Add a new Kconfig option that redirects dfprintk() output to the trace
buffer. This is more efficient than logging to the console and allows
for proper interleaving of dprintk and static tracepoint events.

Since using trace_printk() causes scary warnings to pop at boot time,
this new option defaults to "n".

Signed-off-by: Jeff Layton <jlayton@...nel.org>
---
 include/linux/sunrpc/debug.h | 10 ++++++++--
 net/sunrpc/Kconfig           | 14 ++++++++++++++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/include/linux/sunrpc/debug.h b/include/linux/sunrpc/debug.h
index 99a6fa4a1d6af0b275546a53957f07c9a509f2ac..fd9f79fa534ef001b3ec5e6d7e4b1099843b64a4 100644
--- a/include/linux/sunrpc/debug.h
+++ b/include/linux/sunrpc/debug.h
@@ -30,17 +30,23 @@ extern unsigned int		nlm_debug;
 #if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
 # define ifdebug(fac)		if (unlikely(rpc_debug & RPCDBG_##fac))

+# if IS_ENABLED(CONFIG_SUNRPC_DEBUG_TRACE)
+#  define __sunrpc_printk(fmt, ...)	trace_printk(fmt, ##__VA_ARGS__)
+# else
+#  define __sunrpc_printk(fmt, ...)	pr_default(fmt, ##__VA_ARGS__)
+# endif
+
 # define dfprintk(fac, fmt, ...)					\
 do {									\
 	ifdebug(fac)							\
-		printk(KERN_DEFAULT fmt, ##__VA_ARGS__);				\
+		__sunrpc_printk(fmt, ##__VA_ARGS__);			\
 } while (0)

 # define dfprintk_rcu(fac, fmt, ...)					\
 do {									\
 	ifdebug(fac) {							\
 		rcu_read_lock();					\
-		printk(KERN_DEFAULT fmt, ##__VA_ARGS__);				\
+		__sunrpc_printk(fmt, ##__VA_ARGS__);			\
 		rcu_read_unlock();					\
 	}								\
 } while (0)
diff --git a/net/sunrpc/Kconfig b/net/sunrpc/Kconfig
index 2d8b67dac7b5b58a8a86c3022dd573746fb22547..a570e7adf270fb8976f751266bbffe39ef696c6a 100644
--- a/net/sunrpc/Kconfig
+++ b/net/sunrpc/Kconfig
@@ -101,6 +101,20 @@ config SUNRPC_DEBUG

 	  If unsure, say Y.

+config SUNRPC_DEBUG_TRACE
+	bool "RPC: Send dfprintk() output to the trace buffer"
+	depends on SUNRPC_DEBUG && TRACING
+	default n
+	help
+          dprintk() output can be voluminous, which can overwhelm the
+          kernel's logging facility as it must be sent to the console.
+          This option causes dprintk() output to go to the trace buffer
+          instead of the kernel log.
+
+          This will cause warnings about trace_printk() being used to be
+          logged at boot time, so say N unless you are debugging a problem
+          with sunrpc-based clients or services.
+
 config SUNRPC_XPRT_RDMA
 	tristate "RPC-over-RDMA transport"
 	depends on SUNRPC && INFINIBAND && INFINIBAND_ADDR_TRANS

-- 
2.50.1