29e37d8141
Use of RCU in the idle loop is incorrect, quite a few instances of just that have made their way into mainline, primarily event tracing. The problem with RCU read-side critical sections on CPUs that RCU believes to be idle is that RCU is completely ignoring the CPU, along with any attempts and RCU read-side critical sections. The approaches of eliminating the offending uses and of pushing the definition of idle down beyond the offending uses have both proved impractical. The new approach is to encapsulate offending uses of RCU with rcu_idle_exit() and rcu_idle_enter(), but this requires nesting for code that is invoked both during idle and and during normal execution. Therefore, this commit modifies rcu_idle_enter() and rcu_idle_exit() to permit nesting. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> Acked-by: Deepthi Dharwar <deepthi@linux.vnet.ibm.com>
112 lines
3.8 KiB
C
112 lines
3.8 KiB
C
/*
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* Read-Copy Update definitions shared among RCU implementations.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*
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* Copyright IBM Corporation, 2011
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*
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* Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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*/
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#ifndef __LINUX_RCU_H
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#define __LINUX_RCU_H
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#ifdef CONFIG_RCU_TRACE
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#define RCU_TRACE(stmt) stmt
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#else /* #ifdef CONFIG_RCU_TRACE */
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#define RCU_TRACE(stmt)
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#endif /* #else #ifdef CONFIG_RCU_TRACE */
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/*
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* Process-level increment to ->dynticks_nesting field. This allows for
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* architectures that use half-interrupts and half-exceptions from
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* process context.
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*
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* DYNTICK_TASK_NEST_MASK defines a field of width DYNTICK_TASK_NEST_WIDTH
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* that counts the number of process-based reasons why RCU cannot
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* consider the corresponding CPU to be idle, and DYNTICK_TASK_NEST_VALUE
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* is the value used to increment or decrement this field.
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*
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* The rest of the bits could in principle be used to count interrupts,
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* but this would mean that a negative-one value in the interrupt
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* field could incorrectly zero out the DYNTICK_TASK_NEST_MASK field.
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* We therefore provide a two-bit guard field defined by DYNTICK_TASK_MASK
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* that is set to DYNTICK_TASK_FLAG upon initial exit from idle.
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* The DYNTICK_TASK_EXIT_IDLE value is thus the combined value used upon
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* initial exit from idle.
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*/
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#define DYNTICK_TASK_NEST_WIDTH 7
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#define DYNTICK_TASK_NEST_VALUE ((LLONG_MAX >> DYNTICK_TASK_NEST_WIDTH) + 1)
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#define DYNTICK_TASK_NEST_MASK (LLONG_MAX - DYNTICK_TASK_NEST_VALUE + 1)
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#define DYNTICK_TASK_FLAG ((DYNTICK_TASK_NEST_VALUE / 8) * 2)
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#define DYNTICK_TASK_MASK ((DYNTICK_TASK_NEST_VALUE / 8) * 3)
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#define DYNTICK_TASK_EXIT_IDLE (DYNTICK_TASK_NEST_VALUE + \
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DYNTICK_TASK_FLAG)
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/*
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* debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally
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* by call_rcu() and rcu callback execution, and are therefore not part of the
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* RCU API. Leaving in rcupdate.h because they are used by all RCU flavors.
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*/
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#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
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# define STATE_RCU_HEAD_READY 0
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# define STATE_RCU_HEAD_QUEUED 1
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extern struct debug_obj_descr rcuhead_debug_descr;
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static inline void debug_rcu_head_queue(struct rcu_head *head)
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{
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debug_object_activate(head, &rcuhead_debug_descr);
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debug_object_active_state(head, &rcuhead_debug_descr,
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STATE_RCU_HEAD_READY,
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STATE_RCU_HEAD_QUEUED);
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}
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static inline void debug_rcu_head_unqueue(struct rcu_head *head)
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{
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debug_object_active_state(head, &rcuhead_debug_descr,
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STATE_RCU_HEAD_QUEUED,
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STATE_RCU_HEAD_READY);
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debug_object_deactivate(head, &rcuhead_debug_descr);
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}
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#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
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static inline void debug_rcu_head_queue(struct rcu_head *head)
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{
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}
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static inline void debug_rcu_head_unqueue(struct rcu_head *head)
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{
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}
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#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
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extern void kfree(const void *);
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static inline bool __rcu_reclaim(char *rn, struct rcu_head *head)
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{
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unsigned long offset = (unsigned long)head->func;
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if (__is_kfree_rcu_offset(offset)) {
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RCU_TRACE(trace_rcu_invoke_kfree_callback(rn, head, offset));
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kfree((void *)head - offset);
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return 1;
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} else {
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RCU_TRACE(trace_rcu_invoke_callback(rn, head));
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head->func(head);
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return 0;
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}
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}
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#endif /* __LINUX_RCU_H */
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