Commit f0bdf6d4 authored Feb 15, 2020 by Lai Jiangshan Committed by Paul E. McKenney Apr 27, 2020

rcu: Remove unused ->rcu_read_unlock_special.b.deferred_qs field



The ->rcu_read_unlock_special.b.deferred_qs field is set to true in
rcu_read_unlock_special() but never set to false.  This is not
particularly useful, so this commit removes this field.

The only possible justification for this field is to ease debugging
of RCU deferred quiscent states, but the combination of the other
->rcu_read_unlock_special fields plus ->rcu_blocked_node and of course
->rcu_read_lock_nesting should cover debugging needs.  And if this last
proves incorrect, this patch can always be reverted, along with the
required setting of ->rcu_read_unlock_special.b.deferred_qs to false
in rcu_preempt_deferred_qs_irqrestore().

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

parent 07b4a930

include/linux/sched.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -613,7 +613,7 @@ union rcu_special {
		u8 blocked;
		u8 need_qs;
		u8 exp_hint; /* Hint for performance. */
		u8 deferred_qs;
		u8 pad; /* No garbage from compiler! */
		} b; /* Bits. */
		u32 s; /* Set of bits. */
		};

kernel/rcu/tree_plugin.h

+0 −1

Original line number	Diff line number	Diff line
		@@ -634,7 +634,6 @@ static void rcu_read_unlock_special(struct task_struct *t)
		irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);
		}
		}
		t->rcu_read_unlock_special.b.deferred_qs = true;
		local_irq_restore(flags);
		return;
		}

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