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Revert "rcu: Move PREEMPT_RCU preemption to switch_to() invocation"

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This reverts commit 616c310e83.
(Move PREEMPT_RCU preemption to switch_to() invocation).
Testing by Sasha Levin <levinsasha928@gmail.com> showed that this
can result in deadlock due to invoking the scheduler when one of
the runqueue locks is held.  Because this commit was simply a
performance optimization, revert it.

Reported-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Sasha Levin <levinsasha928@gmail.com>
This commit is contained in:
Paul E. McKenney 2012-07-02 07:08:42 -07:00
parent 6887a4131d
commit cba6d0d64e
8 changed files with 19 additions and 16 deletions
Download patch file Download diff file Expand all files Collapse all files

1
kernel/rcutree.c
View file

@ -201,6 +201,7 @@ void rcu_note_context_switch(int cpu)
{
trace_rcu_utilization("Start context switch");
rcu_sched_qs(cpu);
rcu_preempt_note_context_switch(cpu);
trace_rcu_utilization("End context switch");
}
EXPORT_SYMBOL_GPL(rcu_note_context_switch);

1
kernel/rcutree.h
View file

@ -444,6 +444,7 @@ DECLARE_PER_CPU(char, rcu_cpu_has_work);
/* Forward declarations for rcutree_plugin.h */
static void rcu_bootup_announce(void);
long rcu_batches_completed(void);
static void rcu_preempt_note_context_switch(int cpu);
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
#ifdef CONFIG_HOTPLUG_CPU
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,

14
kernel/rcutree_plugin.h
View file

@ -153,7 +153,7 @@ static void rcu_preempt_qs(int cpu)
*
* Caller must disable preemption.
*/
void rcu_preempt_note_context_switch(void)
static void rcu_preempt_note_context_switch(int cpu)
{
struct task_struct *t = current;
unsigned long flags;
@ -164,7 +164,7 @@ void rcu_preempt_note_context_switch(void)
(t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
/* Possibly blocking in an RCU read-side critical section. */
rdp = __this_cpu_ptr(rcu_preempt_state.rda);
rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
rnp = rdp->mynode;
raw_spin_lock_irqsave(&rnp->lock, flags);
t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
@ -228,7 +228,7 @@ void rcu_preempt_note_context_switch(void)
* means that we continue to block the current grace period.
*/
local_irq_save(flags);
rcu_preempt_qs(smp_processor_id());
rcu_preempt_qs(cpu);
local_irq_restore(flags);
}
@ -1001,6 +1001,14 @@ void rcu_force_quiescent_state(void)
}
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
/*
* Because preemptible RCU does not exist, we never have to check for
* CPUs being in quiescent states.
*/
static void rcu_preempt_note_context_switch(int cpu)
{
}
/*
* Because preemptible RCU does not exist, there are never any preempted
* RCU readers.

1
kernel/sched/core.c
View file

@ -2081,7 +2081,6 @@ context_switch(struct rq *rq, struct task_struct *prev,
#endif
/* Here we just switch the register state and the stack. */
rcu_switch_from(prev);
switch_to(prev, next, prev);
barrier();