![Paul E. McKenney](/assets/img/avatar_default.png)
This patch fixes a bug located by Vegard Nossum with the aid of kmemcheck, updated based on review comments from Nick Piggin, Ingo Molnar, and Andrew Morton. And cleans up the variable-name and function-name language. ;-) The boot CPU runs in the context of its idle thread during boot-up. During this time, idle_cpu(0) will always return nonzero, which will fool Classic and Hierarchical RCU into deciding that a large chunk of the boot-up sequence is a big long quiescent state. This in turn causes RCU to prematurely end grace periods during this time. This patch changes the rcutree.c and rcuclassic.c rcu_check_callbacks() function to ignore the idle task as a quiescent state until the system has started up the scheduler in rest_init(), introducing a new non-API function rcu_idle_now_means_idle() to inform RCU of this transition. RCU maintains an internal rcu_idle_cpu_truthful variable to track this state, which is then used by rcu_check_callback() to determine if it should believe idle_cpu(). Because this patch has the effect of disallowing RCU grace periods during long stretches of the boot-up sequence, this patch also introduces Josh Triplett's UP-only optimization that makes synchronize_rcu() be a no-op if num_online_cpus() returns 1. This allows boot-time code that calls synchronize_rcu() to proceed normally. Note, however, that RCU callbacks registered by call_rcu() will likely queue up until later in the boot sequence. Although rcuclassic and rcutree can also use this same optimization after boot completes, rcupreempt must restrict its use of this optimization to the portion of the boot sequence before the scheduler starts up, given that an rcupreempt RCU read-side critical section may be preeempted. In addition, this patch takes Nick Piggin's suggestion to make the system_state global variable be __read_mostly. Changes since v4: o Changes the name of the introduced function and variable to be less emotional. ;-) Changes since v3: o WARN_ON(nr_context_switches() > 0) to verify that RCU switches out of boot-time mode before the first context switch, as suggested by Nick Piggin. Changes since v2: o Created rcu_blocking_is_gp() internal-to-RCU API that determines whether a call to synchronize_rcu() is itself a grace period. o The definition of rcu_blocking_is_gp() for rcuclassic and rcutree checks to see if but a single CPU is online. o The definition of rcu_blocking_is_gp() for rcupreempt checks to see both if but a single CPU is online and if the system is still in early boot. This allows rcupreempt to again work correctly if running on a single CPU after booting is complete. o Added check to rcupreempt's synchronize_sched() for there being but one online CPU. Tested all three variants both SMP and !SMP, booted fine, passed a short rcutorture test on both x86 and Power. Located-by: Vegard Nossum <vegard.nossum@gmail.com> Tested-by: Vegard Nossum <vegard.nossum@gmail.com> Tested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
336 lines
12 KiB
C
336 lines
12 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion (tree-based version)
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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, 2008
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*
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* Author: Dipankar Sarma <dipankar@in.ibm.com>
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* Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical algorithm
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*
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* Based on the original work by Paul McKenney <paulmck@us.ibm.com>
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* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
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*
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* For detailed explanation of Read-Copy Update mechanism see -
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* Documentation/RCU
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*/
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#ifndef __LINUX_RCUTREE_H
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#define __LINUX_RCUTREE_H
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#include <linux/cache.h>
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#include <linux/spinlock.h>
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#include <linux/threads.h>
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#include <linux/percpu.h>
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#include <linux/cpumask.h>
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#include <linux/seqlock.h>
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/*
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* Define shape of hierarchy based on NR_CPUS and CONFIG_RCU_FANOUT.
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* In theory, it should be possible to add more levels straightforwardly.
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* In practice, this has not been tested, so there is probably some
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* bug somewhere.
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*/
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#define MAX_RCU_LVLS 3
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#define RCU_FANOUT (CONFIG_RCU_FANOUT)
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#define RCU_FANOUT_SQ (RCU_FANOUT * RCU_FANOUT)
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#define RCU_FANOUT_CUBE (RCU_FANOUT_SQ * RCU_FANOUT)
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#if NR_CPUS <= RCU_FANOUT
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# define NUM_RCU_LVLS 1
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# define NUM_RCU_LVL_0 1
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# define NUM_RCU_LVL_1 (NR_CPUS)
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# define NUM_RCU_LVL_2 0
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# define NUM_RCU_LVL_3 0
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#elif NR_CPUS <= RCU_FANOUT_SQ
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# define NUM_RCU_LVLS 2
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# define NUM_RCU_LVL_0 1
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# define NUM_RCU_LVL_1 (((NR_CPUS) + RCU_FANOUT - 1) / RCU_FANOUT)
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# define NUM_RCU_LVL_2 (NR_CPUS)
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# define NUM_RCU_LVL_3 0
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#elif NR_CPUS <= RCU_FANOUT_CUBE
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# define NUM_RCU_LVLS 3
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# define NUM_RCU_LVL_0 1
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# define NUM_RCU_LVL_1 (((NR_CPUS) + RCU_FANOUT_SQ - 1) / RCU_FANOUT_SQ)
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# define NUM_RCU_LVL_2 (((NR_CPUS) + (RCU_FANOUT) - 1) / (RCU_FANOUT))
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# define NUM_RCU_LVL_3 NR_CPUS
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#else
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# error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
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#endif /* #if (NR_CPUS) <= RCU_FANOUT */
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#define RCU_SUM (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3)
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#define NUM_RCU_NODES (RCU_SUM - NR_CPUS)
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/*
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* Dynticks per-CPU state.
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*/
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struct rcu_dynticks {
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int dynticks_nesting; /* Track nesting level, sort of. */
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int dynticks; /* Even value for dynticks-idle, else odd. */
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int dynticks_nmi; /* Even value for either dynticks-idle or */
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/* not in nmi handler, else odd. So this */
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/* remains even for nmi from irq handler. */
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};
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/*
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* Definition for node within the RCU grace-period-detection hierarchy.
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*/
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struct rcu_node {
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spinlock_t lock;
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unsigned long qsmask; /* CPUs or groups that need to switch in */
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/* order for current grace period to proceed.*/
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unsigned long qsmaskinit;
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/* Per-GP initialization for qsmask. */
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unsigned long grpmask; /* Mask to apply to parent qsmask. */
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int grplo; /* lowest-numbered CPU or group here. */
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int grphi; /* highest-numbered CPU or group here. */
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u8 grpnum; /* CPU/group number for next level up. */
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u8 level; /* root is at level 0. */
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struct rcu_node *parent;
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} ____cacheline_internodealigned_in_smp;
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/* Index values for nxttail array in struct rcu_data. */
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#define RCU_DONE_TAIL 0 /* Also RCU_WAIT head. */
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#define RCU_WAIT_TAIL 1 /* Also RCU_NEXT_READY head. */
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#define RCU_NEXT_READY_TAIL 2 /* Also RCU_NEXT head. */
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#define RCU_NEXT_TAIL 3
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#define RCU_NEXT_SIZE 4
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/* Per-CPU data for read-copy update. */
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struct rcu_data {
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/* 1) quiescent-state and grace-period handling : */
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long completed; /* Track rsp->completed gp number */
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/* in order to detect GP end. */
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long gpnum; /* Highest gp number that this CPU */
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/* is aware of having started. */
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long passed_quiesc_completed;
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/* Value of completed at time of qs. */
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bool passed_quiesc; /* User-mode/idle loop etc. */
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bool qs_pending; /* Core waits for quiesc state. */
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bool beenonline; /* CPU online at least once. */
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struct rcu_node *mynode; /* This CPU's leaf of hierarchy */
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unsigned long grpmask; /* Mask to apply to leaf qsmask. */
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/* 2) batch handling */
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/*
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* If nxtlist is not NULL, it is partitioned as follows.
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* Any of the partitions might be empty, in which case the
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* pointer to that partition will be equal to the pointer for
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* the following partition. When the list is empty, all of
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* the nxttail elements point to nxtlist, which is NULL.
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*
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* [*nxttail[RCU_NEXT_READY_TAIL], NULL = *nxttail[RCU_NEXT_TAIL]):
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* Entries that might have arrived after current GP ended
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* [*nxttail[RCU_WAIT_TAIL], *nxttail[RCU_NEXT_READY_TAIL]):
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* Entries known to have arrived before current GP ended
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* [*nxttail[RCU_DONE_TAIL], *nxttail[RCU_WAIT_TAIL]):
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* Entries that batch # <= ->completed - 1: waiting for current GP
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* [nxtlist, *nxttail[RCU_DONE_TAIL]):
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* Entries that batch # <= ->completed
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* The grace period for these entries has completed, and
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* the other grace-period-completed entries may be moved
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* here temporarily in rcu_process_callbacks().
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*/
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struct rcu_head *nxtlist;
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struct rcu_head **nxttail[RCU_NEXT_SIZE];
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long qlen; /* # of queued callbacks */
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long blimit; /* Upper limit on a processed batch */
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#ifdef CONFIG_NO_HZ
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/* 3) dynticks interface. */
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struct rcu_dynticks *dynticks; /* Shared per-CPU dynticks state. */
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int dynticks_snap; /* Per-GP tracking for dynticks. */
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int dynticks_nmi_snap; /* Per-GP tracking for dynticks_nmi. */
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#endif /* #ifdef CONFIG_NO_HZ */
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/* 4) reasons this CPU needed to be kicked by force_quiescent_state */
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#ifdef CONFIG_NO_HZ
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unsigned long dynticks_fqs; /* Kicked due to dynticks idle. */
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#endif /* #ifdef CONFIG_NO_HZ */
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unsigned long offline_fqs; /* Kicked due to being offline. */
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unsigned long resched_ipi; /* Sent a resched IPI. */
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/* 5) state to allow this CPU to force_quiescent_state on others */
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long n_rcu_pending; /* rcu_pending() calls since boot. */
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long n_rcu_pending_force_qs; /* when to force quiescent states. */
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int cpu;
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};
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/* Values for signaled field in struct rcu_state. */
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#define RCU_GP_INIT 0 /* Grace period being initialized. */
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#define RCU_SAVE_DYNTICK 1 /* Need to scan dyntick state. */
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#define RCU_FORCE_QS 2 /* Need to force quiescent state. */
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#ifdef CONFIG_NO_HZ
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#define RCU_SIGNAL_INIT RCU_SAVE_DYNTICK
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#else /* #ifdef CONFIG_NO_HZ */
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#define RCU_SIGNAL_INIT RCU_FORCE_QS
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#endif /* #else #ifdef CONFIG_NO_HZ */
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#define RCU_JIFFIES_TILL_FORCE_QS 3 /* for rsp->jiffies_force_qs */
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#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
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#define RCU_SECONDS_TILL_STALL_CHECK (10 * HZ) /* for rsp->jiffies_stall */
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#define RCU_SECONDS_TILL_STALL_RECHECK (30 * HZ) /* for rsp->jiffies_stall */
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#define RCU_STALL_RAT_DELAY 2 /* Allow other CPUs time */
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/* to take at least one */
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/* scheduling clock irq */
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/* before ratting on them. */
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#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
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/*
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* RCU global state, including node hierarchy. This hierarchy is
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* represented in "heap" form in a dense array. The root (first level)
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* of the hierarchy is in ->node[0] (referenced by ->level[0]), the second
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* level in ->node[1] through ->node[m] (->node[1] referenced by ->level[1]),
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* and the third level in ->node[m+1] and following (->node[m+1] referenced
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* by ->level[2]). The number of levels is determined by the number of
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* CPUs and by CONFIG_RCU_FANOUT. Small systems will have a "hierarchy"
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* consisting of a single rcu_node.
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*/
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struct rcu_state {
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struct rcu_node node[NUM_RCU_NODES]; /* Hierarchy. */
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struct rcu_node *level[NUM_RCU_LVLS]; /* Hierarchy levels. */
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u32 levelcnt[MAX_RCU_LVLS + 1]; /* # nodes in each level. */
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u8 levelspread[NUM_RCU_LVLS]; /* kids/node in each level. */
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struct rcu_data *rda[NR_CPUS]; /* array of rdp pointers. */
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/* The following fields are guarded by the root rcu_node's lock. */
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u8 signaled ____cacheline_internodealigned_in_smp;
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/* Force QS state. */
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long gpnum; /* Current gp number. */
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long completed; /* # of last completed gp. */
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spinlock_t onofflock; /* exclude on/offline and */
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/* starting new GP. */
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spinlock_t fqslock; /* Only one task forcing */
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/* quiescent states. */
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unsigned long jiffies_force_qs; /* Time at which to invoke */
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/* force_quiescent_state(). */
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unsigned long n_force_qs; /* Number of calls to */
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/* force_quiescent_state(). */
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unsigned long n_force_qs_lh; /* ~Number of calls leaving */
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/* due to lock unavailable. */
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unsigned long n_force_qs_ngp; /* Number of calls leaving */
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/* due to no GP active. */
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#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
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unsigned long gp_start; /* Time at which GP started, */
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/* but in jiffies. */
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unsigned long jiffies_stall; /* Time at which to check */
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/* for CPU stalls. */
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#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
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#ifdef CONFIG_NO_HZ
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long dynticks_completed; /* Value of completed @ snap. */
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#endif /* #ifdef CONFIG_NO_HZ */
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};
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extern struct rcu_state rcu_state;
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DECLARE_PER_CPU(struct rcu_data, rcu_data);
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extern struct rcu_state rcu_bh_state;
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DECLARE_PER_CPU(struct rcu_data, rcu_bh_data);
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/*
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* Increment the quiescent state counter.
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* The counter is a bit degenerated: We do not need to know
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* how many quiescent states passed, just if there was at least
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* one since the start of the grace period. Thus just a flag.
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*/
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static inline void rcu_qsctr_inc(int cpu)
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{
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struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
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rdp->passed_quiesc = 1;
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rdp->passed_quiesc_completed = rdp->completed;
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}
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static inline void rcu_bh_qsctr_inc(int cpu)
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{
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struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
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rdp->passed_quiesc = 1;
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rdp->passed_quiesc_completed = rdp->completed;
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}
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extern int rcu_pending(int cpu);
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extern int rcu_needs_cpu(int cpu);
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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extern struct lockdep_map rcu_lock_map;
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# define rcu_read_acquire() \
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lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
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# define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_)
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#else
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# define rcu_read_acquire() do { } while (0)
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# define rcu_read_release() do { } while (0)
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#endif
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static inline void __rcu_read_lock(void)
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{
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preempt_disable();
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__acquire(RCU);
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rcu_read_acquire();
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}
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static inline void __rcu_read_unlock(void)
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{
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rcu_read_release();
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__release(RCU);
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preempt_enable();
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}
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static inline void __rcu_read_lock_bh(void)
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{
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local_bh_disable();
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__acquire(RCU_BH);
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rcu_read_acquire();
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}
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static inline void __rcu_read_unlock_bh(void)
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{
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rcu_read_release();
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__release(RCU_BH);
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local_bh_enable();
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}
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#define __synchronize_sched() synchronize_rcu()
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#define call_rcu_sched(head, func) call_rcu(head, func)
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static inline void rcu_init_sched(void)
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{
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}
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extern void __rcu_init(void);
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extern void rcu_check_callbacks(int cpu, int user);
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extern void rcu_restart_cpu(int cpu);
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extern long rcu_batches_completed(void);
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extern long rcu_batches_completed_bh(void);
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#ifdef CONFIG_NO_HZ
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void rcu_enter_nohz(void);
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void rcu_exit_nohz(void);
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#else /* CONFIG_NO_HZ */
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static inline void rcu_enter_nohz(void)
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{
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}
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static inline void rcu_exit_nohz(void)
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{
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}
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#endif /* CONFIG_NO_HZ */
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/* A context switch is a grace period for rcutree. */
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static inline int rcu_blocking_is_gp(void)
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{
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return num_online_cpus() == 1;
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}
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#endif /* __LINUX_RCUTREE_H */
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