The following commit has been merged into the core/rcu branch of tip:
Commit-ID: bde50d8ff83e4ce9e576f7c5ba1edb48a3610a5b
Gitweb: https://git.kernel.org/tip/bde50d8ff83e4ce9e576f7c5ba1edb48a3610a5b
Author: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
AuthorDate: Tue, 26 May 2020 15:41:34 +02:00
Committer: Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Mon, 29 Jun 2020 12:01:22 -07:00
srcu: Avoid local_irq_save() before acquiring spinlock_t
SRCU disables interrupts to get a stable per-CPU pointer and then
acquires the spinlock which is in the per-CPU data structure. The
release uses spin_unlock_irqrestore(). While this is correct on a non-RT
kernel, this conflicts with the RT semantics because the spinlock is
converted to a 'sleeping' spinlock. Sleeping locks can obviously not be
acquired with interrupts disabled.
Acquire the per-CPU pointer `ssp->sda' without disabling preemption and
then acquire the spinlock_t of the per-CPU data structure. The lock will
ensure that the data is consistent.
The added call to check_init_srcu_struct() is now needed because a
statically defined srcu_struct may remain uninitialized until this
point and the newly introduced locking operation requires an initialized
spinlock_t.
This change was tested for four hours with 8*SRCU-N and 8*SRCU-P without
causing any warnings.
Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: rcu@xxxxxxxxxxxxxxx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
kernel/rcu/srcutree.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 8ff71e5..c100acf 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -777,14 +777,15 @@ static bool srcu_might_be_idle(struct srcu_struct *ssp)
unsigned long t;
unsigned long tlast;
+ check_init_srcu_struct(ssp);
/* If the local srcu_data structure has callbacks, not idle. */
- local_irq_save(flags);
- sdp = this_cpu_ptr(ssp->sda);
+ sdp = raw_cpu_ptr(ssp->sda);
+ spin_lock_irqsave_rcu_node(sdp, flags);
if (rcu_segcblist_pend_cbs(&sdp->srcu_cblist)) {
- local_irq_restore(flags);
+ spin_unlock_irqrestore_rcu_node(sdp, flags);
return false; /* Callbacks already present, so not idle. */
}
- local_irq_restore(flags);
+ spin_unlock_irqrestore_rcu_node(sdp, flags);
/*
* No local callbacks, so probabalistically probe global state.
@@ -864,9 +865,8 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
}
rhp->func = func;
idx = srcu_read_lock(ssp);
- local_irq_save(flags);
- sdp = this_cpu_ptr(ssp->sda);
- spin_lock_rcu_node(sdp);
+ sdp = raw_cpu_ptr(ssp->sda);
+ spin_lock_irqsave_rcu_node(sdp, flags);
rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
rcu_segcblist_advance(&sdp->srcu_cblist,
rcu_seq_current(&ssp->srcu_gp_seq));
|