keys: fix lost wakeup when reaping a dead key type

clear_bit() is atomic with respect to the word it modifies, but it is
an unordered operation: it implies no memory barrier on either side
(Documentation/atomic_bitops.txt).

key_garbage_collector() clears KEY_GC_REAPING_KEYTYPE with clear_bit()
and calls wake_up_bit() after reaping a dead key type. wake_up_bit()
uses a lockless waitqueue check and requires a full barrier after the
clear.

The existing smp_mb() is before clear_bit(), so nothing orders the clear
against that check. The GC can see an empty waitqueue while
unregister_key_type() still sees the bit set. The final wakeup is then
lost, leaving module unload stuck in wait_on_bit().

Use clear_and_wake_up_bit(). Its clear_bit_unlock() has RELEASE
semantics, so the completed GC work stays ordered before the clear, and
its smp_mb__after_atomic() orders the clear before the waitqueue check.

Fixes: 0c061b5707ab ("KEYS: Correctly destroy key payloads when their keytype is removed")
Assisted-by: Claude:claude-fable-5
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
Link: https://lore.kernel.org/r/20260821025327.61488-1-kmehltretter@gmail.com
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

0 files changed, 0 insertions, 0 deletions