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 5/6] srcu: Provide polling interfaces for Tree SRCU grace periods
Date: Fri, 20 Nov 2020 16:59:18 -0800 [thread overview]
Message-ID: <20201121005919.17152-5-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, so this commit supplies get_state_synchronize_srcu(),
start_poll_synchronize_srcu(), and poll_state_synchronize_srcu() for this
purpose. The first can be used if future grace periods are inevitable
(perhaps due to a later call_srcu() invocation), the second if future
grace periods might not otherwise happen, and the third to check if a
grace period has elapsed since the corresponding call to either of the
first two.
As with get_state_synchronize_rcu() and cond_synchronize_rcu(),
the return value from either get_state_synchronize_srcu() or
start_poll_synchronize_srcu() must be passed in to a later call to
poll_state_synchronize_srcu().
Link: https://lore.kernel.org/rcu/20201112201547.GF3365678@moria.home.lan/
Reported-by: Kent Overstreet <kent.overstreet@gmail.com>
[ paulmck: Add EXPORT_SYMBOL_GPL() per kernel test robot feedback. ]
[ paulmck: Apply feedback from Neeraj Upadhyay. ]
Link: https://lore.kernel.org/lkml/20201117004017.GA7444@paulmck-ThinkPad-P72/
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/srcutiny.c | 2 +-
kernel/rcu/srcutree.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++++---
2 files changed, 64 insertions(+), 5 deletions(-)
diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index b073175..c8f4202 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -148,7 +148,7 @@ void srcu_drive_gp(struct work_struct *wp)
* straighten that out.
*/
WRITE_ONCE(ssp->srcu_gp_running, false);
- if (USHORT_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)))
+ if (USHORT_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)))
schedule_work(&ssp->srcu_work);
}
EXPORT_SYMBOL_GPL(srcu_drive_gp);
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index d930ece..945c047 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -810,7 +810,8 @@ static void srcu_leak_callback(struct rcu_head *rhp)
/*
* Start an SRCU grace period, and also queue the callback if non-NULL.
*/
-static void srcu_gp_start_if_needed(struct srcu_struct *ssp, struct rcu_head *rhp, bool do_norm)
+static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
+ struct rcu_head *rhp, bool do_norm)
{
unsigned long flags;
int idx;
@@ -819,10 +820,12 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp, struct rcu_head *rh
unsigned long s;
struct srcu_data *sdp;
+ check_init_srcu_struct(ssp);
idx = srcu_read_lock(ssp);
sdp = raw_cpu_ptr(ssp->sda);
spin_lock_irqsave_rcu_node(sdp, flags);
- rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
+ if (rhp)
+ rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
rcu_segcblist_advance(&sdp->srcu_cblist,
rcu_seq_current(&ssp->srcu_gp_seq));
s = rcu_seq_snap(&ssp->srcu_gp_seq);
@@ -841,6 +844,7 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp, struct rcu_head *rh
else if (needexp)
srcu_funnel_exp_start(ssp, sdp->mynode, s);
srcu_read_unlock(ssp, idx);
+ return s;
}
/*
@@ -874,7 +878,6 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp, struct rcu_head *rh
static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
rcu_callback_t func, bool do_norm)
{
- check_init_srcu_struct(ssp);
if (debug_rcu_head_queue(rhp)) {
/* Probable double call_srcu(), so leak the callback. */
WRITE_ONCE(rhp->func, srcu_leak_callback);
@@ -882,7 +885,7 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
return;
}
rhp->func = func;
- srcu_gp_start_if_needed(ssp, rhp, do_norm);
+ (void)srcu_gp_start_if_needed(ssp, rhp, do_norm);
}
/**
@@ -1011,6 +1014,62 @@ void synchronize_srcu(struct srcu_struct *ssp)
}
EXPORT_SYMBOL_GPL(synchronize_srcu);
+/**
+ * get_state_synchronize_srcu - Provide an end-of-grace-period cookie
+ * @ssp: srcu_struct to provide cookie for.
+ *
+ * This function returns a cookie that can be passed to
+ * poll_state_synchronize_srcu(), which will return true if a full grace
+ * period has elapsed in the meantime. It is the caller's responsibility
+ * to make sure that grace period happens, for example, by invoking
+ * call_srcu() after return from get_state_synchronize_srcu().
+ */
+unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp)
+{
+ // Any prior manipulation of SRCU-protected data must happen
+ // before the load from ->srcu_gp_seq.
+ smp_mb();
+ return rcu_seq_snap(&ssp->srcu_gp_seq);
+}
+EXPORT_SYMBOL_GPL(get_state_synchronize_srcu);
+
+/**
+ * start_poll_synchronize_srcu - Provide cookie and start grace period
+ * @ssp: srcu_struct to provide cookie for.
+ *
+ * This function returns a cookie that can be passed to
+ * poll_state_synchronize_srcu(), which will return true if a full grace
+ * period has elapsed in the meantime. Unlike get_state_synchronize_srcu(),
+ * this function also ensures that any needed SRCU grace period will be
+ * started. This convenience does come at a cost in terms of CPU overhead.
+ */
+unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp)
+{
+ return srcu_gp_start_if_needed(ssp, NULL, true);
+}
+EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu);
+
+/**
+ * poll_state_synchronize_srcu - Has cookie's grace period ended?
+ * @ssp: srcu_struct to provide cookie for.
+ * @cookie: Return value from get_state_synchronize_srcu() or start_poll_synchronize_srcu().
+ *
+ * This function takes the cookie that was returned from either
+ * get_state_synchronize_srcu() or start_poll_synchronize_srcu(), and
+ * returns @true if an SRCU grace period elapsed since the time that the
+ * cookie was created.
+ */
+bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie)
+{
+ if (!rcu_seq_done(&ssp->srcu_gp_seq, cookie))
+ return false;
+ // Ensure that the end of the SRCU grace period happens before
+ // any subsequent code that the caller might execute.
+ smp_mb(); // ^^^
+ return true;
+}
+EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);
+
/*
* Callback function for srcu_barrier() use.
*/
--
2.9.5
next prev parent reply other threads:[~2020-11-21 0:59 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <@@@>
2017-06-06 17:07 ` [PATCH v2 tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context Paul E. McKenney
2017-06-06 17:07 ` [PATCH v2 tip/core/rcu 2/2] srcu: Allow use of Classic " Paul E. McKenney
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 ` [PATCH v2 tip/core/rcu 1/6] srcu: Make Tiny SRCU use multi-bit grace-period counter paulmck
2020-11-23 4:31 ` 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 ` paulmck [this message]
2020-11-27 4:52 ` [PATCH v2 tip/core/rcu 5/6] srcu: Provide polling interfaces for Tree " 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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