From 74612a07b83fc46c2b2e6f71a541d55b024ebefc Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 12 Nov 2020 16:34:09 -0800 Subject: srcu: Make Tiny SRCU use multi-bit grace-period counter There is a need for a polling interface for SRCU grace periods. This polling needs to distinguish between an SRCU instance being idle on the one hand or in the middle of a grace period on the other. This commit therefore converts the Tiny SRCU srcu_struct structure's srcu_idx from a defacto boolean to a free-running counter, using the bottom bit to indicate that a grace period is in progress. The second-from-bottom bit is thus used as the index returned by srcu_read_lock(). Link: https://lore.kernel.org/rcu/20201112201547.GF3365678@moria.home.lan/ Reported-by: Kent Overstreet [ paulmck: Fix ->srcu_lock_nesting[] indexing per Neeraj Upadhyay. ] Reviewed-by: Neeraj Upadhyay Signed-off-by: Paul E. McKenney --- kernel/rcu/srcutiny.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'kernel') diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c index 6208c1dae5c9..5598cf6f1edc 100644 --- a/kernel/rcu/srcutiny.c +++ b/kernel/rcu/srcutiny.c @@ -124,11 +124,12 @@ void srcu_drive_gp(struct work_struct *wp) ssp->srcu_cb_head = NULL; ssp->srcu_cb_tail = &ssp->srcu_cb_head; local_irq_enable(); - idx = ssp->srcu_idx; - WRITE_ONCE(ssp->srcu_idx, !ssp->srcu_idx); + idx = (ssp->srcu_idx & 0x2) / 2; + WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); WRITE_ONCE(ssp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */ swait_event_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx])); WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */ + WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); /* Invoke the callbacks we removed above. */ while (lh) { -- cgit v1.2.3