linux-kernel - [PATCH] driver core: make device_set_deferred_probe_reason a no-op when !CONFIG_DEBUG

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Date:   Mon, 19 Apr 2021 12:42:56 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Andrzej Hajda <a.hajda@...sung.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] driver core: make device_set_deferred_probe_reason a no-op when !CONFIG_DEBUG_FS

When debugfs is not enabled, the deferred_probe_reason string is never
read. So there's no reason to spend time and memory on recording it.

There's still a bunch of redundant kfree(NULL) calls and NULL
assignments, but this gives most of the benefit (avoiding two
vsnprintf() and a kmalloc()) for the minimal amount of ifdeffery.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 drivers/base/dd.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 37a5e5f8b221..6a197336c6a4 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -216,9 +216,13 @@ void device_unblock_probing(void)
  * device_set_deferred_probe_reason() - Set defer probe reason message for device
  * @dev: the pointer to the struct device
  * @vaf: the pointer to va_format structure with message
+ *
+ * The ->deferred_probe_reason string is only ever read when debugfs
+ * is enabled, so this is a no-op for !CONFIG_DEBUG_FS.
  */
 void device_set_deferred_probe_reason(const struct device *dev, struct va_format *vaf)
 {
+#ifdef CONFIG_DEBUG_FS
 	const char *drv = dev_driver_string(dev);
 
 	mutex_lock(&deferred_probe_mutex);
@@ -227,6 +231,7 @@ void device_set_deferred_probe_reason(const struct device *dev, struct va_format
 	dev->p->deferred_probe_reason = kasprintf(GFP_KERNEL, "%s: %pV", drv, vaf);
 
 	mutex_unlock(&deferred_probe_mutex);
+#endif
 }
 
 /*
-- 
2.29.2