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rcu: Report QS for outermost PREEMPT=n rcu_read_unlock() for strict GPs
The CONFIG_PREEMPT=n instance of rcu_read_unlock is even more aggressively than that of CONFIG_PREEMPT=y in deferring reporting quiescent states to the RCU core. This is just what is wanted in normal use because it reduces overhead, but the resulting delay is not what is wanted for kernels built with CONFIG_RCU_STRICT_GRACE_PERIOD=y. This commit therefore adds an rcu_read_unlock_strict() function that checks for exceptional conditions, and reports the newly started quiescent state if it is safe to do so, also doing a spin-delay if requested via rcutree.rcu_unlock_delay. This commit also adds a call to rcu_read_unlock_strict() from the CONFIG_PREEMPT=n instance of __rcu_read_unlock(). [ paulmck: Fixed bug located by kernel test robot <lkp@intel.com> ] Reported-by Jann Horn <jannh@google.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
parent
a657f26170
commit
aa40c138cc
3 changed files with 31 additions and 6 deletions
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@ -55,6 +55,12 @@ void __rcu_read_unlock(void);
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#else /* #ifdef CONFIG_PREEMPT_RCU */
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#ifdef CONFIG_TINY_RCU
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#define rcu_read_unlock_strict() do { } while (0)
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#else
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void rcu_read_unlock_strict(void);
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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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@ -63,6 +69,7 @@ static inline void __rcu_read_lock(void)
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static inline void __rcu_read_unlock(void)
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{
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preempt_enable();
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rcu_read_unlock_strict();
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}
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static inline int rcu_preempt_depth(void)
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@ -178,6 +178,12 @@ module_param(gp_init_delay, int, 0444);
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static int gp_cleanup_delay;
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module_param(gp_cleanup_delay, int, 0444);
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// Add delay to rcu_read_unlock() for strict grace periods.
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static int rcu_unlock_delay;
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#ifdef CONFIG_RCU_STRICT_GRACE_PERIOD
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module_param(rcu_unlock_delay, int, 0444);
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#endif
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/*
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* This rcu parameter is runtime-read-only. It reflects
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* a minimum allowed number of objects which can be cached
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@ -430,12 +430,6 @@ static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
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return !list_empty(&rnp->blkd_tasks);
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}
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// Add delay to rcu_read_unlock() for strict grace periods.
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static int rcu_unlock_delay;
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#ifdef CONFIG_RCU_STRICT_GRACE_PERIOD
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module_param(rcu_unlock_delay, int, 0444);
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#endif
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/*
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* Report deferred quiescent states. The deferral time can
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* be quite short, for example, in the case of the call from
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@ -784,6 +778,24 @@ dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
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#else /* #ifdef CONFIG_PREEMPT_RCU */
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/*
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* If strict grace periods are enabled, and if the calling
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* __rcu_read_unlock() marks the beginning of a quiescent state, immediately
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* report that quiescent state and, if requested, spin for a bit.
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*/
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void rcu_read_unlock_strict(void)
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{
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struct rcu_data *rdp;
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if (!IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ||
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irqs_disabled() || preempt_count() || !rcu_state.gp_kthread)
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return;
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rdp = this_cpu_ptr(&rcu_data);
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rcu_report_qs_rdp(rdp->cpu, rdp);
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udelay(rcu_unlock_delay);
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}
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EXPORT_SYMBOL_GPL(rcu_read_unlock_strict);
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/*
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* Tell them what RCU they are running.
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*/
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