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rcutorture: Add test of holding scheduler locks across rcu_read_unlock()

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Now that it should be safe to hold scheduler locks across
rcu_read_unlock(), even in cases where the corresponding RCU read-side
critical section might have been preempted and boosted, the commit adds
a test of this capability to rcutorture.  This has been tested on current
mainline (which can deadlock in this situation), and lockdep duly reported
the expected deadlock.  On -rcu, lockdep is silent, thus far, anyway.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2020-03-28 18:53:25 -07:00
parent 5f5fa7ea89
commit 52b1fc3f79
1 changed files with 9 additions and 1 deletions
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10
kernel/rcu/rcutorture.c
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@ -1147,6 +1147,7 @@ static void rcutorture_one_extend(int *readstate, int newstate,
struct torture_random_state *trsp,
struct rt_read_seg *rtrsp)
{
unsigned long flags;
int idxnew = -1;
int idxold = *readstate;
int statesnew = ~*readstate & newstate;
@ -1181,8 +1182,15 @@ static void rcutorture_one_extend(int *readstate, int newstate,
rcu_read_unlock_bh();
if (statesold & RCUTORTURE_RDR_SCHED)
rcu_read_unlock_sched();
if (statesold & RCUTORTURE_RDR_RCU)
if (statesold & RCUTORTURE_RDR_RCU) {
bool lockit = !statesnew && !(torture_random(trsp) & 0xffff);
if (lockit)
raw_spin_lock_irqsave(&current->pi_lock, flags);
cur_ops->readunlock(idxold >> RCUTORTURE_RDR_SHIFT);
if (lockit)
raw_spin_unlock_irqrestore(&current->pi_lock, flags);
}
/* Delay if neither beginning nor end and there was a change. */
if ((statesnew || statesold) && *readstate && newstate)