From: "Paul E. McKenney" <paulmck@xxxxxxxxxx> Because Tiny RCU is used only in kernels built with either CONFIG_PREEMPT_NONE=y or CONFIG_PREEMPT_VOLUNTARY=y, there has not been any need for TINY RCU to explicitly disable preemption. However, the prospect of lazy preemption changes that, and preemption means that the non-atomic increment in synchronize_rcu() can be preempted, with the possibility that one of the increments is lost. This could cause failures for users of the APIs that poll RCU grace periods. This commit therefore adds the needed preempt_disable() and preempt_enable() call to Tiny RCU. Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> Cc: Ankur Arora <ankur.a.arora@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx> --- kernel/rcu/tiny.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c index 4470af926a34..4402d6f5f857 100644 --- a/kernel/rcu/tiny.c +++ b/kernel/rcu/tiny.c @@ -153,7 +153,9 @@ void synchronize_rcu(void) lock_is_held(&rcu_lock_map) || lock_is_held(&rcu_sched_lock_map), "Illegal synchronize_rcu() in RCU read-side critical section"); + preempt_disable(); WRITE_ONCE(rcu_ctrlblk.gp_seq, rcu_ctrlblk.gp_seq + 2); + preempt_enable(); } EXPORT_SYMBOL_GPL(synchronize_rcu); -- 2.39.2
