From: paulmck@kernel.org
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
mingo@kernel.org, jiangshanlai@gmail.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
kent.overstreet@gmail.com,
"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH v2 tip/core/rcu 1/6] srcu: Make Tiny SRCU use multi-bit grace-period counter
Date: Fri, 20 Nov 2020 16:59:14 -0800 [thread overview]
Message-ID: <20201121005919.17152-1-paulmck@kernel.org> (raw)
In-Reply-To: <@@@>
From: "Paul E. McKenney" <paulmck@kernel.org>
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_read_lock() idx computation Neeraj per Upadhyay. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
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;
}
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) {
--
2.9.5
next prev parent reply other threads:[~2020-11-21 0:59 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <@@@>
2020-02-14 23:38 ` [PATCH tip/core/rcu 1/9] doc: Add some more RCU list patterns in the kernel paulmck
2020-02-14 23:38 ` [PATCH tip/core/rcu 2/9] doc/RCU/Design: Remove remaining HTML tags in ReST files paulmck
2020-02-14 23:38 ` [PATCH tip/core/rcu 3/9] doc/RCU/listRCU: Fix typos in a example code snippets paulmck
2020-02-14 23:38 ` [PATCH tip/core/rcu 4/9] doc/RCU/listRCU: Update example function name paulmck
2020-02-14 23:38 ` [PATCH tip/core/rcu 5/9] doc/RCU/rcu: Use ':ref:' for links to other docs paulmck
2020-02-14 23:39 ` [PATCH tip/core/rcu 6/9] doc/RCU/rcu: Use absolute paths for non-rst files paulmck
2020-02-14 23:39 ` [PATCH tip/core/rcu 7/9] doc/RCU/rcu: Use https instead of http if possible paulmck
2020-02-14 23:39 ` [PATCH tip/core/rcu 8/9] doc: Add rcutorture scripting to torture.txt paulmck
2020-02-14 23:39 ` [PATCH tip/core/rcu 9/9] Documentation/memory-barriers: Fix typos paulmck
2020-11-21 0:59 ` paulmck [this message]
2020-11-23 4:31 ` [PATCH v2 tip/core/rcu 1/6] srcu: Make Tiny SRCU use multi-bit grace-period counter Neeraj Upadhyay
2020-11-23 19:55 ` Paul E. McKenney
2020-11-24 5:18 ` Neeraj Upadhyay
2020-11-25 4:33 ` Neeraj Upadhyay
2020-11-28 2:16 ` Paul E. McKenney
2020-11-28 4:12 ` Neeraj Upadhyay
2020-11-21 0:59 ` [PATCH v2 tip/core/rcu 2/6] srcu: Provide internal interface to start a Tiny SRCU grace period paulmck
2020-11-21 0:59 ` [PATCH v2 tip/core/rcu 3/6] srcu: Provide internal interface to start a Tree " paulmck
2020-11-21 0:59 ` [PATCH v2 tip/core/rcu 4/6] srcu: Provide polling interfaces for Tiny SRCU grace periods paulmck
2020-11-22 14:30 ` Neeraj Upadhyay
2020-11-22 17:57 ` Paul E. McKenney
2020-11-23 4:43 ` Neeraj Upadhyay
2020-11-23 21:12 ` Paul E. McKenney
2020-11-24 5:14 ` Neeraj Upadhyay
2020-11-24 19:30 ` Paul E. McKenney
2020-11-25 4:39 ` Neeraj Upadhyay
2020-11-21 0:59 ` [PATCH v2 tip/core/rcu 5/6] srcu: Provide polling interfaces for Tree " paulmck
2020-11-27 4:52 ` Neeraj Upadhyay
2020-11-21 0:59 ` [PATCH v2 tip/core/rcu 6/6] srcu: Document " paulmck
2020-11-27 8:27 ` Neeraj Upadhyay
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