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| author | Paul E. McKenney <paulmck@kernel.org> | 2020-11-12 16:34:09 -0800 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2021-01-04 13:53:36 -0800 |
| commit | 74612a07b83fc46c2b2e6f71a541d55b024ebefc (patch) | |
| tree | 22b7b70daa6adc9227083ff6381815f2aa1712a8 /kernel | |
| parent | 5c8fe583cce542aa0b84adc939ce85293de36e5e (diff) | |
| download | lwn-74612a07b83fc46c2b2e6f71a541d55b024ebefc.tar.gz lwn-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')
| -rw-r--r-- | kernel/rcu/srcutiny.c | 5 |
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) { |