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| author | Dmitry Ilvokhin <d@ilvokhin.com> | 2026-06-02 10:12:53 +0300 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2026-06-03 12:38:48 +0300 |
| commit | a13ab9dd6eb2a89f14b466c3884730ea7969253f (patch) | |
| tree | e7e5ac5e2898ce7bc23514d4164a574f04c380d6 /include/linux | |
| parent | 22302af28d3f7c3ca38536978c80db51d2a9e283 (diff) | |
| download | linux-a13ab9dd6eb2a89f14b466c3884730ea7969253f.tar.xz | |
cleanup: Remove NULL check from unconditional guards
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 2deccd5c862a ("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
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/cleanup.h | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h index 4e60d519713c..65416938e318 100644 --- a/include/linux/cleanup.h +++ b/include/linux/cleanup.h @@ -398,7 +398,7 @@ static __maybe_unused const bool class_##_name##_is_conditional = _is_cond #define DEFINE_GUARD(_name, _type, _lock, _unlock) \ static __always_inline __nonnull_args() _type class_##_name##_constructor(_type _T); \ - DEFINE_CLASS(_name, _type, if (_T) { _unlock; }, ({ _lock; _T; }), _type _T); \ + DEFINE_CLASS(_name, _type, _unlock, ({ _lock; _T; }), _type _T); \ DEFINE_CLASS_IS_GUARD(_name) #define DEFINE_GUARD_COND_4(_name, _ext, _lock, _cond) \ @@ -492,7 +492,7 @@ typedef struct { \ static __always_inline void class_##_name##_destructor(class_##_name##_t *_T) \ __no_context_analysis \ { \ - if (_T->lock) { _unlock; } \ + _unlock; \ } \ \ __DEFINE_GUARD_LOCK_PTR(_name, &_T->lock) |