linux-kernel - [PATCH 1/2] Revert "drivers: core: synchronize really_probe() and dev

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Message-ID: <20250220064647.2437048-1-dmitry.torokhov@gmail.com>
Date: Wed, 19 Feb 2025 22:46:44 -0800
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
	Danilo Krummrich <dakr@...nel.org>,
	linux-kernel@...r.kernel.org,
	"Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
	Dirk Behme <dirk.behme@...bosch.com>
Subject: [PATCH 1/2] Revert "drivers: core: synchronize really_probe() and dev_uevent()"

This reverts commit c0a40097f0bc81deafc15f9195d1fb54595cd6d0.

Probing a device can take arbitrary long time. In the field we observed
that, for example, probing a bad micro-SD cards in an external USB card
reader (or maybe cards were good but cables were flaky) sometimes takes
longer than 2 minutes due to multiple retries at various levels of the
stack. We can not block uevent_show() method for that long because udev
is reading that attribute very often and that blocks udev and interferes
with booting of the system.

The change that introduced locking was concerned with dev_uevent()
racing with unbinding the driver. However we can handle it without
locking (which will be done in subsequent patch).

There was also claim that synchronization with probe() is needed to
properly load USB drivers, however this is a red herring: the change
adding the lock was introduced in May of last year and USB loading and
probing worked properly for many years before that.

Revert the harmful locking.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
---
 drivers/base/core.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 5a1f05198114..9f4d4868e3b4 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -2725,11 +2725,8 @@ static ssize_t uevent_show(struct device *dev, struct device_attribute *attr,
 	if (!env)
 		return -ENOMEM;

-	/* Synchronize with really_probe() */
-	device_lock(dev);
 	/* let the kset specific function add its keys */
 	retval = kset->uevent_ops->uevent(&dev->kobj, env);
-	device_unlock(dev);
 	if (retval)
 		goto out;

-- 
2.48.1.601.g30ceb7b040-goog