From fc2219d49ef1606e7fd2c88af2b423b01ff3d319 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 23 Sep 2009 09:50:41 -0700 Subject: rcu: Clean up code based on review feedback from Josh Triplett These issues identified during an old-fashioned face-to-face code review extended over many hours. o Bury various forms of the "rsp->completed == rsp->gpnum" comparison into an rcu_gp_in_progress() function, which has the beneficial side-effect of forcing consistent use of ACCESS_ONCE(). o Replace hand-coded arithmetic with DIV_ROUND_UP(). o Bury several "!list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x01])" instances into an rcu_preempted_readers() function, as this expression indicates that there are no readers blocked within RCU read-side critical sections blocking the current grace period. (Though there might well be similar readers blocking the next grace period.) o Remove a dangling rcu_restart_cpu() declaration that has been dangling for almost 20 minor releases of the kernel. Signed-off-by: Paul E. McKenney Acked-by: Peter Zijlstra Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12537246442687-git-send-email-> Signed-off-by: Ingo Molnar --- kernel/rcutree_plugin.h | 50 ++++++++++++++++++++++++------------------------- 1 file changed, 25 insertions(+), 25 deletions(-) (limited to 'kernel/rcutree_plugin.h') diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 1cee04f627e..8ff1ba7b3c4 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -150,6 +150,16 @@ void __rcu_read_lock(void) } EXPORT_SYMBOL_GPL(__rcu_read_lock); +/* + * Check for preempted RCU readers blocking the current grace period + * for the specified rcu_node structure. If the caller needs a reliable + * answer, it must hold the rcu_node's ->lock. + */ +static int rcu_preempted_readers(struct rcu_node *rnp) +{ + return !list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]); +} + static void rcu_read_unlock_special(struct task_struct *t) { int empty; @@ -196,7 +206,7 @@ static void rcu_read_unlock_special(struct task_struct *t) break; spin_unlock(&rnp->lock); /* irqs remain disabled. */ } - empty = list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]); + empty = !rcu_preempted_readers(rnp); list_del_init(&t->rcu_node_entry); t->rcu_blocked_node = NULL; @@ -207,7 +217,7 @@ static void rcu_read_unlock_special(struct task_struct *t) * drop rnp->lock and restore irq. */ if (!empty && rnp->qsmask == 0 && - list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1])) { + !rcu_preempted_readers(rnp)) { struct rcu_node *rnp_p; if (rnp->parent == NULL) { @@ -257,12 +267,12 @@ static void rcu_print_task_stall(struct rcu_node *rnp) { unsigned long flags; struct list_head *lp; - int phase = rnp->gpnum & 0x1; + int phase; struct task_struct *t; - if (!list_empty(&rnp->blocked_tasks[phase])) { + if (rcu_preempted_readers(rnp)) { spin_lock_irqsave(&rnp->lock, flags); - phase = rnp->gpnum & 0x1; /* re-read under lock. */ + phase = rnp->gpnum & 0x1; lp = &rnp->blocked_tasks[phase]; list_for_each_entry(t, lp, rcu_node_entry) printk(" P%d", t->pid); @@ -281,20 +291,10 @@ static void rcu_print_task_stall(struct rcu_node *rnp) */ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) { - WARN_ON_ONCE(!list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1])); + WARN_ON_ONCE(rcu_preempted_readers(rnp)); WARN_ON_ONCE(rnp->qsmask); } -/* - * Check for preempted RCU readers for the specified rcu_node structure. - * If the caller needs a reliable answer, it must hold the rcu_node's - * >lock. - */ -static int rcu_preempted_readers(struct rcu_node *rnp) -{ - return !list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]); -} - #ifdef CONFIG_HOTPLUG_CPU /* @@ -461,6 +461,15 @@ static void rcu_preempt_note_context_switch(int cpu) { } +/* + * Because preemptable RCU does not exist, there are never any preempted + * RCU readers. + */ +static int rcu_preempted_readers(struct rcu_node *rnp) +{ + return 0; +} + #ifdef CONFIG_RCU_CPU_STALL_DETECTOR /* @@ -483,15 +492,6 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) WARN_ON_ONCE(rnp->qsmask); } -/* - * Because preemptable RCU does not exist, there are never any preempted - * RCU readers. - */ -static int rcu_preempted_readers(struct rcu_node *rnp) -{ - return 0; -} - #ifdef CONFIG_HOTPLUG_CPU /* -- cgit v1.2.3-18-g5258 From 1eba8f84380bede3c602bd7758dea96925cead01 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 23 Sep 2009 09:50:42 -0700 Subject: rcu: Clean up code based on review feedback from Josh Triplett, part 2 These issues identified during an old-fashioned face-to-face code review extending over many hours. o Add comments for tricky parts of code, and correct comments that have passed their sell-by date. o Get rid of the vestiges of rcu_init_sched(), which is no longer needed now that PREEMPT_RCU is gone. o Move the #include of rcutree_plugin.h to the end of rcutree.c, which means that, rather than having a random collection of forward declarations, the new set of forward declarations document the set of plugins. The new home for this #include also allows __rcu_init_preempt() to move into rcutree_plugin.h. o Fix rcu_preempt_check_callbacks() to be static. Suggested-by: Josh Triplett Signed-off-by: Paul E. McKenney Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12537246443924-git-send-email-> Signed-off-by: Ingo Molnar Peter Zijlstra --- kernel/rcutree_plugin.h | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-) (limited to 'kernel/rcutree_plugin.h') diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 8ff1ba7b3c4..65250219ab6 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -418,6 +418,18 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu) rcu_init_percpu_data(cpu, &rcu_preempt_state, 1); } +/* + * Initialize preemptable RCU's state structures. + */ +static void __init __rcu_init_preempt(void) +{ + int i; /* All used by RCU_INIT_FLAVOR(). */ + int j; + struct rcu_node *rnp; + + RCU_INIT_FLAVOR(&rcu_preempt_state, rcu_preempt_data); +} + /* * Check for a task exiting while in a preemptable-RCU read-side * critical section, clean up if so. No need to issue warnings, @@ -518,7 +530,7 @@ static void rcu_preempt_offline_cpu(int cpu) * Because preemptable RCU does not exist, it never has any callbacks * to check. */ -void rcu_preempt_check_callbacks(int cpu) +static void rcu_preempt_check_callbacks(int cpu) { } @@ -526,7 +538,7 @@ void rcu_preempt_check_callbacks(int cpu) * Because preemptable RCU does not exist, it never has any callbacks * to process. */ -void rcu_preempt_process_callbacks(void) +static void rcu_preempt_process_callbacks(void) { } @@ -563,4 +575,11 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu) { } +/* + * Because preemptable RCU does not exist, it need not be initialized. + */ +static void __init __rcu_init_preempt(void) +{ +} + #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ -- cgit v1.2.3-18-g5258 From a0b6c9a78c41dc36732d6e1e90f0f2f57b29816f Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 28 Sep 2009 07:46:33 -0700 Subject: rcu: Clean up code based on review feedback from Josh Triplett, part 4 These issues identified during an old-fashioned face-to-face code review extending over many hours. This group improves an existing abstraction and introduces two new ones. It also fixes an RCU stall-warning bug found while making the other changes. o Make RCU_INIT_FLAVOR() declare its own variables, removing the need to declare them at each call site. o Create an rcu_for_each_leaf() macro that scans the leaf nodes of the rcu_node tree. o Create an rcu_for_each_node_breadth_first() macro that does a breadth-first traversal of the rcu_node tree, AKA stepping through the array in index-number order. o If all CPUs corresponding to a given leaf rcu_node structure go offline, then any tasks queued on that leaf will be moved to the root rcu_node structure. Therefore, the stall-warning code must dump out tasks queued on the root rcu_node structure as well as those queued on the leaf rcu_node structures. Signed-off-by: Paul E. McKenney Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12541491934126-git-send-email-> Signed-off-by: Ingo Molnar --- kernel/rcutree_plugin.h | 4 ---- 1 file changed, 4 deletions(-) (limited to 'kernel/rcutree_plugin.h') diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 65250219ab6..57200fe96d0 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -423,10 +423,6 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu) */ static void __init __rcu_init_preempt(void) { - int i; /* All used by RCU_INIT_FLAVOR(). */ - int j; - struct rcu_node *rnp; - RCU_INIT_FLAVOR(&rcu_preempt_state, rcu_preempt_data); } -- cgit v1.2.3-18-g5258 From e74f4c4564455c91a3b4075bb1721993c2a95dda Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 6 Oct 2009 21:48:17 -0700 Subject: rcu: Make hot-unplugged CPU relinquish its own RCU callbacks The current interaction between RCU and CPU hotplug requires that RCU block in CPU notifiers waiting for callbacks to drain. This can be greatly simplified by having each CPU relinquish its own callbacks, and for both _rcu_barrier() and CPU_DEAD notifiers to adopt all callbacks that were previously relinquished. This change also eliminates the possibility of certain types of hangs due to the previous practice of waiting for callbacks to be invoked from within CPU notifiers. If you don't every wait, you cannot hang. Signed-off-by: Paul E. McKenney Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1254890898456-git-send-email-> Signed-off-by: Ingo Molnar --- kernel/rcutree_plugin.h | 34 ++++++++++++++++++++++++++++++++++ 1 file changed, 34 insertions(+) (limited to 'kernel/rcutree_plugin.h') diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 57200fe96d0..c0cb783aa16 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -410,6 +410,15 @@ static int rcu_preempt_needs_cpu(int cpu) return !!per_cpu(rcu_preempt_data, cpu).nxtlist; } +/** + * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. + */ +void rcu_barrier(void) +{ + _rcu_barrier(&rcu_preempt_state, call_rcu); +} +EXPORT_SYMBOL_GPL(rcu_barrier); + /* * Initialize preemptable RCU's per-CPU data. */ @@ -418,6 +427,14 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu) rcu_init_percpu_data(cpu, &rcu_preempt_state, 1); } +/* + * Move preemptable RCU's callbacks to ->orphan_cbs_list. + */ +static void rcu_preempt_send_cbs_to_orphanage(void) +{ + rcu_send_cbs_to_orphanage(&rcu_preempt_state); +} + /* * Initialize preemptable RCU's state structures. */ @@ -563,6 +580,16 @@ static int rcu_preempt_needs_cpu(int cpu) return 0; } +/* + * Because preemptable RCU does not exist, rcu_barrier() is just + * another name for rcu_barrier_sched(). + */ +void rcu_barrier(void) +{ + rcu_barrier_sched(); +} +EXPORT_SYMBOL_GPL(rcu_barrier); + /* * Because preemptable RCU does not exist, there is no per-CPU * data to initialize. @@ -571,6 +598,13 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu) { } +/* + * Because there is no preemptable RCU, there are no callbacks to move. + */ +static void rcu_preempt_send_cbs_to_orphanage(void) +{ +} + /* * Because preemptable RCU does not exist, it need not be initialized. */ -- cgit v1.2.3-18-g5258