I noticed that the atomic_dec_and_lock_irqsave() in put_ucounts() loops sometimes even during boot. Something like 2-3 iterations but still. This series replaces the refcounting with rcuref_t and adds a RCU lookup. This allows a lockless lookup in alloc_ucounts() if the entry is available and a cmpxchg()less put of the item.
Patch #1 adds HLIST_NULLS_HEAD_INIT for which I added the RCU folks. Sebastian Sebastian Andrzej Siewior (4): rcu: Provide a static initializer for hlist_nulls_head. ucount: Replace get_ucounts_or_wrap() with atomic_inc_not_zero(). ucount: Use RCU for ucounts lookups. ucount: Use rcuref_t for reference counting. include/linux/list_nulls.h | 1 + include/linux/user_namespace.h | 15 ++++-- kernel/ucount.c | 97 +++++++++++++++------------------- 3 files changed, 55 insertions(+), 58 deletions(-) -- 2.47.2
