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Curtis Klein b9bced8ca7 watchdog: set cdev owner before adding 
[ Upstream commit 38d7529774 ]

When the new watchdog character device is registered, it becomes
available for opening. This creates a race where userspace may open the
device before the character device's owner is set. This results in an
imbalance in module_get calls as the cdev_get in cdev_open will not
increment the reference count on the watchdog driver module.

This causes problems when the watchdog character device is released as
the module loader's reference will also be released. This makes it
impossible to open the watchdog device later on as it now appears that
the module is being unloaded. The open will fail with -ENXIO from
chrdev_open.

The legacy watchdog device will fail with -EBUSY from the try_module_get
in watchdog_open because it's module owner is the watchdog core module
so it can still be opened but it will fail to get a refcount on the
underlying watchdog device driver.

Fixes: 72139dfa24 ("watchdog: Fix the race between the release of watchdog_core_data and cdev")
Signed-off-by: Curtis Klein <curtis.klein@hpe.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20231205190522.55153-1-curtis.klein@hpe.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2024-01-25 14:52:44 -08:00
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README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.