cleanup: Remove NULL check from unconditional guards

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The unconditional guard destructors check whether the lock pointer is
NULL before unlocking. This check is dead code because unconditional
guards guarantee a non-NULL lock pointer at destructor time.

DEFINE_GUARD() runs the lock operation unconditionally in the
constructor. If the pointer were NULL, the lock operation (e.g.
mutex_lock(NULL)) would crash before the constructor returns. The
destructor never runs with a NULL pointer. All DEFINE_GUARD() users
dereference the pointer in their lock. Verified by auditing every
instance found by: git grep -n -A 1 'DEFINE_GUARD('. The only exception
is xe_pm_runtime_release_only, whose constructor is a noop, but it has
no callers.

__DEFINE_UNLOCK_GUARD() has only a few usages outside of
include/linux/cleanup.h: tty_port_tty (NULL-checks in its tty_kref_put()
call), irqdesc_lock (fixed earlier) and two guards in
kernel/sched/sched.h (dereference the pointer unconditionally in their
lock constructors).

DEFINE_LOCK_GUARD_1() sets .lock from its argument and runs the lock
operation in the constructor. Same reasoning applies. All
DEFINE_LOCK_GUARD_1() users dereference the pointer in their lock. Also,
verified by auditing every match of: git grep -n 'DEFINE_LOCK_GUARD_1('.

DEFINE_LOCK_GUARD_0() hardcodes .lock = (void *)1 in the constructor,
so it is never NULL by construction.

Conditional (_try) variants: DEFINE_GUARD_COND() and
DEFINE_LOCK_GUARD_1_COND() use EXTEND_CLASS_COND(), whose wrapper
destructor returns early when the lock was not acquired, before reaching
the base destructor since commit 2deccd5c86 ("cleanup: Optimize
guards"):

    if (_cond) return; class_##_name##_destructor(_T);

As compiled by GCC-11 with defconfig on top of the locking/core:

    Total: Before=23889980, After=23834334, chg -0.23%

Signed-off-by: Dmitry Ilvokhin <d@ilvokhin.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/0503a089389b2270c478a873e095cf0a4ff26d24.1780064327.git.d@ilvokhin.com

...

This commit is contained in:

Dmitry Ilvokhin 2026-06-02 07:12:53 +00:00 • committed by Peter Zijlstra

parent 22302af28d

commit a13ab9dd6e

1 changed files with 2 additions and 2 deletions

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include/linux/cleanup.h

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