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rcu-tasks: Allow rcu_read_unlock_trace() under scheduler locks

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The rcu_read_unlock_trace() can invoke rcu_read_unlock_trace_special(),
which in turn can call wake_up().  Therefore, if any scheduler lock is
held across a call to rcu_read_unlock_trace(), self-deadlock can occur.
This commit therefore uses the irq_work facility to defer the wake_up()
to a clean environment where no scheduler locks will be held.

Reported-by: Steven Rostedt <rostedt@goodmis.org>
[ paulmck: Update #includes for m68k per kbuild test robot. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2020-03-20 14:29:08 -07:00
parent 7d0c9c50c5
commit b38f57c1fe
2 changed files with 12 additions and 1 deletions
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12
kernel/rcu/tasks.h
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@ -729,6 +729,16 @@ void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func);
DEFINE_RCU_TASKS(rcu_tasks_trace, rcu_tasks_wait_gp, call_rcu_tasks_trace,
"RCU Tasks Trace");
/*
* This irq_work handler allows rcu_read_unlock_trace() to be invoked
* while the scheduler locks are held.
*/
static void rcu_read_unlock_iw(struct irq_work *iwp)
{
wake_up(&trc_wait);
}
static DEFINE_IRQ_WORK(rcu_tasks_trace_iw, rcu_read_unlock_iw);
/* If we are the last reader, wake up the grace-period kthread. */
void rcu_read_unlock_trace_special(struct task_struct *t, int nesting)
{
@ -742,7 +752,7 @@ void rcu_read_unlock_trace_special(struct task_struct *t, int nesting)
WRITE_ONCE(t->trc_reader_special.b.need_qs, false);
WRITE_ONCE(t->trc_reader_nesting, nesting);
if (nq && atomic_dec_and_test(&trc_n_readers_need_end))
wake_up(&trc_wait);
irq_work_queue(&rcu_tasks_trace_iw);
}
EXPORT_SYMBOL_GPL(rcu_read_unlock_trace_special);

1
kernel/rcu/update.c
View file

@ -41,6 +41,7 @@
#include <linux/sched/isolation.h>
#include <linux/kprobes.h>
#include <linux/slab.h>
#include <linux/irq_work.h>
#define CREATE_TRACE_POINTS