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rcu: Create RCU-specific workqueues with rescuers

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RCU's expedited grace periods can participate in out-of-memory deadlocks
due to all available system_wq kthreads being blocked and there not being
memory available to create more.  This commit prevents such deadlocks
by allocating an RCU-specific workqueue_struct at early boot time, and
providing it with a rescuer to ensure forward progress.  This uses the
shiny new init_rescuer() function provided by Tejun (but indirectly).

This commit also causes SRCU to use this new RCU-specific
workqueue_struct.  Note that SRCU's use of workqueues never blocks them
waiting for readers, so this should be safe from a forward-progress
viewpoint.  Note that this moves SRCU from system_power_efficient_wq
to a normal workqueue.  In the unlikely event that this results in
measurable degradation, a separate power-efficient workqueue will be
creates for SRCU.

Reported-by: Prateek Sood <prsood@codeaurora.org>
Reported-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Paul E. McKenney
2018-01-08 14:35:52 -08:00
parent 65963d2461
commit ad7c946b35
4 changed files with 11 additions and 6 deletions
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6
kernel/rcu/tree.c
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@@ -4167,6 +4167,8 @@ static void __init rcu_dump_rcu_node_tree(struct rcu_state *rsp)
pr_cont("\n");
}
struct workqueue_struct *rcu_gp_wq;
void __init rcu_init(void)
{
int cpu;
@@ -4193,6 +4195,10 @@ void __init rcu_init(void)
rcu_cpu_starting(cpu);
rcutree_online_cpu(cpu);
}
/* Create workqueue for expedited GPs and for Tree SRCU. */
rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
WARN_ON(!rcu_gp_wq);
}
#include "tree_exp.h"