On 11/24/2020 1:25 AM, Paul E. McKenney wrote:
On Mon, Nov 23, 2020 at 10:01:13AM +0530, Neeraj Upadhyay wrote:
On 11/21/2020 6:29 AM, paulmck@xxxxxxxxxx wrote:
From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
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@xxxxxxxxxxxxxx/
Reported-by: Kent Overstreet <kent.overstreet@xxxxxxxxx>
[ paulmck: Fix __srcu_read_lock() idx computation Neeraj per Upadhyay. ]
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
include/linux/srcutiny.h | 4 ++--
kernel/rcu/srcutiny.c | 5 +++--
2 files changed, 5 insertions(+), 4 deletions(-)
diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
index 5a5a194..d9edb67 100644
--- a/include/linux/srcutiny.h
+++ b/include/linux/srcutiny.h
@@ -15,7 +15,7 @@
struct srcu_struct {
short srcu_lock_nesting[2]; /* srcu_read_lock() nesting depth. */
- short srcu_idx; /* Current reader array element. */
+ unsigned short srcu_idx; /* Current reader array element in bit 0x2. */
u8 srcu_gp_running; /* GP workqueue running? */
u8 srcu_gp_waiting; /* GP waiting for readers? */
struct swait_queue_head srcu_wq;
@@ -59,7 +59,7 @@ static inline int __srcu_read_lock(struct srcu_struct *ssp)
{
int idx;
- idx = READ_ONCE(ssp->srcu_idx);
+ idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
WRITE_ONCE(ssp->srcu_lock_nesting[idx], ssp->srcu_lock_nesting[idx] + 1);
return idx;
}
Need change in idx calcultion in srcu_torture_stats_print() ?
static inline void srcu_torture_stats_print(struct srcu_struct *ssp,
idx = READ_ONCE(ssp->srcu_idx) & 0x1;
Excellent point! It should match the calculation in __srcu_read_lock(),
shouldn't it? I have updated this, thank you!
Thanx, Paul
Updated version looks good!
Thanks
Neeraj
Thanks
Neeraj
diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index 6208c1d..5598cf6 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) {
--
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--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
member of the Code Aurora Forum, hosted by The Linux Foundation
