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authorPaul E. McKenney <paulmck@kernel.org>2020-11-13 01:34:09 +0100
committerPaul E. McKenney <paulmck@kernel.org>2021-01-04 22:53:36 +0100
commit74612a07b83fc46c2b2e6f71a541d55b024ebefc (patch)
tree22b7b70daa6adc9227083ff6381815f2aa1712a8 /kernel/rcu
parentLinux 5.11-rc1 (diff)
downloadlinux-74612a07b83fc46c2b2e6f71a541d55b024ebefc.tar.xz
linux-74612a07b83fc46c2b2e6f71a541d55b024ebefc.zip
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 <kent.overstreet@gmail.com> [ paulmck: Fix ->srcu_lock_nesting[] indexing per Neeraj Upadhyay. ] Reviewed-by: Neeraj Upadhyay <neeraju@codeaurora.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu')
-rw-r--r--kernel/rcu/srcutiny.c5
1 files changed, 3 insertions, 2 deletions
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) {