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Prevent a race vs. statically initialized objects. Such objects are
usually not initialized via an init() function. They are special cased
and detected on first use under the assumption that they are already
correctly initialized via the static initializer.
This works correctly unless there are two concurrent debug object
operations on such an object.
The first one detects that the object is not yet tracked and tries to
establish a tracking object after dropping the debug objects hash bucket
lock. The concurrent operation does the same. The one which wins the
race ends up modifying the state of the object which makes the other one
fail resulting in a bogus debug objects warning.
Prevent this by making the detection of a static object and the
allocation of a tracking object atomic under the hash bucket lock. So the
first one to acquire the hash bucket lock will succeed and the second one
will observe the correct tracking state.
This race existed forever but was only exposed when the timer wheel code
added a debug_object_assert_init() call outside of the timer base locked
region. This replaced the previous warning about timer::function being
NULL which had to be removed when the timer_shutdown() mechanics were
added.
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Merge tag 'core-debugobjects-2023-04-24' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull core debugobjects update from Thomas Gleixner:
"A single update to debugobjects:
Prevent a race vs statically initialized objects. Such objects are
usually not initialized via an init() function. They are special cased
and detected on first use under the assumption that they are already
correctly initialized via the static initializer.
This works correctly unless there are two concurrent debug object
operations on such an object.
The first one detects that the object is not yet tracked and tries to
establish a tracking object after dropping the debug objects hash
bucket lock. The concurrent operation does the same. The one which
wins the race ends up modifying the state of the object which makes
the other one fail resulting in a bogus debug objects warning.
Prevent this by making the detection of a static object and the
allocation of a tracking object atomic under the hash bucket lock. So
the first one to acquire the hash bucket lock will succeed and the
second one will observe the correct tracking state.
This race existed forever but was only exposed when the timer wheel
code added a debug_object_assert_init() call outside of the timer base
locked region. This replaced the previous warning about
timer::function being NULL which had to be removed when the
timer_shutdown() mechanics were added"
* tag 'core-debugobjects-2023-04-24' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
debugobject: Prevent init race with static objects
29e95a4b26