rcu: merge TREE_PREEPT_RCU blocked_tasks[] lists (12f5f524) · Commits · 戴 / test

Documentation/RCU/trace.txt

+18 −11

Original line number	Diff line number	Diff line
		@@ -166,14 +166,14 @@ o "gpnum" is the number of grace periods that have started. It is
		The output of "cat rcu/rcuhier" looks as follows, with very long lines:

		c=6902 g=6903 s=2 jfq=3 j=72c7 nfqs=13142/nfqsng=0(13142) fqlh=6
		1/1 .>. 0:127 ^0
		3/3 .>. 0:35 ^0 0/0 .>. 36:71 ^1 0/0 .>. 72:107 ^2 0/0 .>. 108:127 ^3
		3/3f .>. 0:5 ^0 2/3 .>. 6:11 ^1 0/0 .>. 12:17 ^2 0/0 .>. 18:23 ^3 0/0 .>. 24:29 ^4 0/0 .>. 30:35 ^5 0/0 .>. 36:41 ^0 0/0 .>. 42:47 ^1 0/0 .>. 48:53 ^2 0/0 .>. 54:59 ^3 0/0 .>. 60:65 ^4 0/0 .>. 66:71 ^5 0/0 .>. 72:77 ^0 0/0 .>. 78:83 ^1 0/0 .>. 84:89 ^2 0/0 .>. 90:95 ^3 0/0 .>. 96:101 ^4 0/0 .>. 102:107 ^5 0/0 .>. 108:113 ^0 0/0 .>. 114:119 ^1 0/0 .>. 120:125 ^2 0/0 .>. 126:127 ^3
		1/1 ..>. 0:127 ^0
		3/3 ..>. 0:35 ^0 0/0 ..>. 36:71 ^1 0/0 ..>. 72:107 ^2 0/0 ..>. 108:127 ^3
		3/3f ..>. 0:5 ^0 2/3 ..>. 6:11 ^1 0/0 ..>. 12:17 ^2 0/0 ..>. 18:23 ^3 0/0 ..>. 24:29 ^4 0/0 ..>. 30:35 ^5 0/0 ..>. 36:41 ^0 0/0 ..>. 42:47 ^1 0/0 ..>. 48:53 ^2 0/0 ..>. 54:59 ^3 0/0 ..>. 60:65 ^4 0/0 ..>. 66:71 ^5 0/0 ..>. 72:77 ^0 0/0 ..>. 78:83 ^1 0/0 ..>. 84:89 ^2 0/0 ..>. 90:95 ^3 0/0 ..>. 96:101 ^4 0/0 ..>. 102:107 ^5 0/0 ..>. 108:113 ^0 0/0 ..>. 114:119 ^1 0/0 ..>. 120:125 ^2 0/0 ..>. 126:127 ^3
		rcu_bh:
		c=-226 g=-226 s=1 jfq=-5701 j=72c7 nfqs=88/nfqsng=0(88) fqlh=0
		0/1 .>. 0:127 ^0
		0/3 .>. 0:35 ^0 0/0 .>. 36:71 ^1 0/0 .>. 72:107 ^2 0/0 .>. 108:127 ^3
		0/3f .>. 0:5 ^0 0/3 .>. 6:11 ^1 0/0 .>. 12:17 ^2 0/0 .>. 18:23 ^3 0/0 .>. 24:29 ^4 0/0 .>. 30:35 ^5 0/0 .>. 36:41 ^0 0/0 .>. 42:47 ^1 0/0 .>. 48:53 ^2 0/0 .>. 54:59 ^3 0/0 .>. 60:65 ^4 0/0 .>. 66:71 ^5 0/0 .>. 72:77 ^0 0/0 .>. 78:83 ^1 0/0 .>. 84:89 ^2 0/0 .>. 90:95 ^3 0/0 .>. 96:101 ^4 0/0 .>. 102:107 ^5 0/0 .>. 108:113 ^0 0/0 .>. 114:119 ^1 0/0 .>. 120:125 ^2 0/0 .>. 126:127 ^3
		0/1 ..>. 0:127 ^0
		0/3 ..>. 0:35 ^0 0/0 ..>. 36:71 ^1 0/0 ..>. 72:107 ^2 0/0 ..>. 108:127 ^3
		0/3f ..>. 0:5 ^0 0/3 ..>. 6:11 ^1 0/0 ..>. 12:17 ^2 0/0 ..>. 18:23 ^3 0/0 ..>. 24:29 ^4 0/0 ..>. 30:35 ^5 0/0 ..>. 36:41 ^0 0/0 ..>. 42:47 ^1 0/0 ..>. 48:53 ^2 0/0 ..>. 54:59 ^3 0/0 ..>. 60:65 ^4 0/0 ..>. 66:71 ^5 0/0 ..>. 72:77 ^0 0/0 ..>. 78:83 ^1 0/0 ..>. 84:89 ^2 0/0 ..>. 90:95 ^3 0/0 ..>. 96:101 ^4 0/0 ..>. 102:107 ^5 0/0 ..>. 108:113 ^0 0/0 ..>. 114:119 ^1 0/0 ..>. 120:125 ^2 0/0 ..>. 126:127 ^3

		This is once again split into "rcu_sched" and "rcu_bh" portions,
		and CONFIG_TREE_PREEMPT_RCU kernels will again have an additional
		@@ -232,13 +232,20 @@ o Each element of the form "1/1 0:127 ^0" represents one struct
		current grace period.

		o The characters separated by the ">" indicate the state
		of the blocked-tasks lists. A "T" preceding the ">"
		of the blocked-tasks lists. A "G" preceding the ">"
		indicates that at least one task blocked in an RCU
		read-side critical section blocks the current grace
		period, while a "." preceding the ">" indicates otherwise.
		The character following the ">" indicates similarly for
		the next grace period. A "T" should appear in this
		field only for rcu-preempt.
		period, while a "E" preceding the ">" indicates that
		at least one task blocked in an RCU read-side critical
		section blocks the current expedited grace period.
		A "T" character following the ">" indicates that at
		least one task is blocked within an RCU read-side
		critical section, regardless of whether any current
		grace period (expedited or normal) is inconvenienced.
		A "." character appears if the corresponding condition
		does not hold, so that "..>." indicates that no tasks
		are blocked. In contrast, "GE>T" indicates maximal
		inconvenience from blocked tasks.

		o The numbers separated by the ":" are the range of CPUs
		served by this struct rcu_node. This can be helpful

kernel/rcutree.c

+1 −4

Original line number	Diff line number	Diff line
		@@ -1901,10 +1901,7 @@ static void __init rcu_init_one(struct rcu_state *rsp,
		j / rsp->levelspread[i - 1];
		}
		rnp->level = i;
		INIT_LIST_HEAD(&rnp->blocked_tasks[0]);
		INIT_LIST_HEAD(&rnp->blocked_tasks[1]);
		INIT_LIST_HEAD(&rnp->blocked_tasks[2]);
		INIT_LIST_HEAD(&rnp->blocked_tasks[3]);
		INIT_LIST_HEAD(&rnp->blkd_tasks);
		}
		}

kernel/rcutree.h

+15 −6

Original line number	Diff line number	Diff line
		@@ -107,7 +107,7 @@ struct rcu_node {
		/* an rcu_data structure, otherwise, each */
		/* bit corresponds to a child rcu_node */
		/* structure. */
		unsigned long expmask; /* Groups that have ->blocked_tasks[] */
		unsigned long expmask; /* Groups that have ->blkd_tasks */
		/* elements that need to drain to allow the */
		/* current expedited grace period to */
		/* complete (only for TREE_PREEMPT_RCU). */
		@@ -120,11 +120,20 @@ struct rcu_node {
		u8 grpnum; /* CPU/group number for next level up. */
		u8 level; /* root is at level 0. */
		struct rcu_node *parent;
		struct list_head blocked_tasks[4];
		/* Tasks blocked in RCU read-side critsect. */
		/* Grace period number (->gpnum) x blocked */
		/* by tasks on the (x & 0x1) element of the */
		/* blocked_tasks[] array. */
		struct list_head blkd_tasks;
		/* Tasks blocked in RCU read-side critical */
		/* section. Tasks are placed at the head */
		/* of this list and age towards the tail. */
		struct list_head *gp_tasks;
		/* Pointer to the first task blocking the */
		/* current grace period, or NULL if there */
		/* is no such task. */
		struct list_head *exp_tasks;
		/* Pointer to the first task blocking the */
		/* current expedited grace period, or NULL */
		/* if there is no such task. If there */
		/* is no current expedited grace period, */
		/* then there can cannot be any such task. */
		} ____cacheline_internodealigned_in_smp;

		/*

kernel/rcutree_plugin.h

+97 −66

Original line number	Diff line number	Diff line
		@@ -130,12 +130,12 @@ static void rcu_preempt_qs(int cpu)
		* We have entered the scheduler, and the current task might soon be
		* context-switched away from. If this task is in an RCU read-side
		* critical section, we will no longer be able to rely on the CPU to
		* record that fact, so we enqueue the task on the appropriate entry
		* of the blocked_tasks[] array. The task will dequeue itself when
		* it exits the outermost enclosing RCU read-side critical section.
		* Therefore, the current grace period cannot be permitted to complete
		* until the blocked_tasks[] entry indexed by the low-order bit of
		* rnp->gpnum empties.
		* record that fact, so we enqueue the task on the blkd_tasks list.
		* The task will dequeue itself when it exits the outermost enclosing
		* RCU read-side critical section. Therefore, the current grace period
		* cannot be permitted to complete until the blkd_tasks list entries
		* predating the current grace period drain, in other words, until
		* rnp->gp_tasks becomes NULL.
		*
		* Caller must disable preemption.
		*/
		@@ -143,7 +143,6 @@ static void rcu_preempt_note_context_switch(int cpu)
		{
		struct task_struct *t = current;
		unsigned long flags;
		int phase;
		struct rcu_data *rdp;
		struct rcu_node *rnp;

		@@ -165,15 +164,26 @@ static void rcu_preempt_note_context_switch(int cpu)
		* (i.e., this CPU has not yet passed through a quiescent
		* state for the current grace period), then as long
		* as that task remains queued, the current grace period
		* cannot end.
		* cannot end. Note that there is some uncertainty as
		* to exactly when the current grace period started.
		* We take a conservative approach, which can result
		* in unnecessarily waiting on tasks that started very
		* slightly after the current grace period began. C'est
		* la vie!!!
		*
		* But first, note that the current CPU must still be
		* on line!
		*/
		WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
		WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
		phase = (rnp->gpnum + !(rnp->qsmask & rdp->grpmask)) & 0x1;
		list_add(&t->rcu_node_entry, &rnp->blocked_tasks[phase]);
		if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
		list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
		rnp->gp_tasks = &t->rcu_node_entry;
		} else {
		list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
		if (rnp->qsmask & rdp->grpmask)
		rnp->gp_tasks = &t->rcu_node_entry;
		}
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
		}

		@@ -210,10 +220,7 @@ EXPORT_SYMBOL_GPL(__rcu_read_lock);
		*/
		static int rcu_preempted_readers(struct rcu_node *rnp)
		{
		int phase = rnp->gpnum & 0x1;

		return !list_empty(&rnp->blocked_tasks[phase]) \|\|
		!list_empty(&rnp->blocked_tasks[phase + 2]);
		return rnp->gp_tasks != NULL;
		}

		/*
		@@ -252,6 +259,21 @@ static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
		rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
		}

		/*
		* Advance a ->blkd_tasks-list pointer to the next entry, instead
		* returning NULL if at the end of the list.
		*/
		static struct list_head rcu_next_node_entry(struct task_struct t,
		struct rcu_node *rnp)
		{
		struct list_head *np;

		np = t->rcu_node_entry.next;
		if (np == &rnp->blkd_tasks)
		np = NULL;
		return np;
		}

		/*
		* Handle special cases during rcu_read_unlock(), such as needing to
		* notify RCU core processing or task having blocked during the RCU
		@@ -262,6 +284,7 @@ static void rcu_read_unlock_special(struct task_struct *t)
		int empty;
		int empty_exp;
		unsigned long flags;
		struct list_head *np;
		struct rcu_node *rnp;
		int special;

		@@ -305,7 +328,12 @@ static void rcu_read_unlock_special(struct task_struct *t)
		empty = !rcu_preempted_readers(rnp);
		empty_exp = !rcu_preempted_readers_exp(rnp);
		smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
		np = rcu_next_node_entry(t, rnp);
		list_del_init(&t->rcu_node_entry);
		if (&t->rcu_node_entry == rnp->gp_tasks)
		rnp->gp_tasks = np;
		if (&t->rcu_node_entry == rnp->exp_tasks)
		rnp->exp_tasks = np;
		t->rcu_blocked_node = NULL;

		/*
		@@ -361,19 +389,17 @@ EXPORT_SYMBOL_GPL(__rcu_read_unlock);
		static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
		{
		unsigned long flags;
		struct list_head *lp;
		int phase;
		struct task_struct *t;

		if (rcu_preempted_readers(rnp)) {
		if (!rcu_preempted_readers(rnp))
		return;
		raw_spin_lock_irqsave(&rnp->lock, flags);
		phase = rnp->gpnum & 0x1;
		lp = &rnp->blocked_tasks[phase];
		list_for_each_entry(t, lp, rcu_node_entry)
		t = list_entry(rnp->gp_tasks,
		struct task_struct, rcu_node_entry);
		list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
		sched_show_task(t);
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
		}
		}

		/*
		* Dump detailed information for all tasks blocking the current RCU
		@@ -402,17 +428,15 @@ static void rcu_print_detail_task_stall(struct rcu_state *rsp)
		*/
		static void rcu_print_task_stall(struct rcu_node *rnp)
		{
		struct list_head *lp;
		int phase;
		struct task_struct *t;

		if (rcu_preempted_readers(rnp)) {
		phase = rnp->gpnum & 0x1;
		lp = &rnp->blocked_tasks[phase];
		list_for_each_entry(t, lp, rcu_node_entry)
		if (!rcu_preempted_readers(rnp))
		return;
		t = list_entry(rnp->gp_tasks,
		struct task_struct, rcu_node_entry);
		list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
		printk(" P%d", t->pid);
		}
		}

		/*
		* Suppress preemptible RCU's CPU stall warnings by pushing the
		@@ -430,10 +454,15 @@ static void rcu_preempt_stall_reset(void)
		* period that still has RCU readers blocked! This function must be
		* invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
		* must be held by the caller.
		*
		* Also, if there are blocked tasks on the list, they automatically
		* block the newly created grace period, so set up ->gp_tasks accordingly.
		*/
		static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
		{
		WARN_ON_ONCE(rcu_preempted_readers(rnp));
		if (!list_empty(&rnp->blkd_tasks))
		rnp->gp_tasks = rnp->blkd_tasks.next;
		WARN_ON_ONCE(rnp->qsmask);
		}

		@@ -457,45 +486,49 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
		struct rcu_node *rnp,
		struct rcu_data *rdp)
		{
		int i;
		struct list_head *lp;
		struct list_head *lp_root;
		int retval = 0;
		struct rcu_node *rnp_root = rcu_get_root(rsp);
		struct task_struct *tp;
		struct task_struct *t;

		if (rnp == rnp_root) {
		WARN_ONCE(1, "Last CPU thought to be offlined?");
		return 0; /* Shouldn't happen: at least one CPU online. */
		}
		WARN_ON_ONCE(rnp != rdp->mynode &&
		(!list_empty(&rnp->blocked_tasks[0]) \|\|
		!list_empty(&rnp->blocked_tasks[1]) \|\|
		!list_empty(&rnp->blocked_tasks[2]) \|\|
		!list_empty(&rnp->blocked_tasks[3])));

		/* If we are on an internal node, complain bitterly. */
		WARN_ON_ONCE(rnp != rdp->mynode);

		/*
		* Move tasks up to root rcu_node. Rely on the fact that the
		* root rcu_node can be at most one ahead of the rest of the
		* rcu_nodes in terms of gp_num value. This fact allows us to
		* move the blocked_tasks[] array directly, element by element.
		* Move tasks up to root rcu_node. Don't try to get fancy for
		* this corner-case operation -- just put this node's tasks
		* at the head of the root node's list, and update the root node's
		* ->gp_tasks and ->exp_tasks pointers to those of this node's,
		* if non-NULL. This might result in waiting for more tasks than
		* absolutely necessary, but this is a good performance/complexity
		* tradeoff.
		*/
		if (rcu_preempted_readers(rnp))
		retval \|= RCU_OFL_TASKS_NORM_GP;
		if (rcu_preempted_readers_exp(rnp))
		retval \|= RCU_OFL_TASKS_EXP_GP;
		for (i = 0; i < 4; i++) {
		lp = &rnp->blocked_tasks[i];
		lp_root = &rnp_root->blocked_tasks[i];
		lp = &rnp->blkd_tasks;
		lp_root = &rnp_root->blkd_tasks;
		while (!list_empty(lp)) {
		tp = list_entry(lp->next, typeof(*tp), rcu_node_entry);
		t = list_entry(lp->next, typeof(*t), rcu_node_entry);
		raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
		list_del(&tp->rcu_node_entry);
		tp->rcu_blocked_node = rnp_root;
		list_add(&tp->rcu_node_entry, lp_root);
		raw_spin_unlock(&rnp_root->lock); /* irqs remain disabled */
		}
		}
		list_del(&t->rcu_node_entry);
		t->rcu_blocked_node = rnp_root;
		list_add(&t->rcu_node_entry, lp_root);
		if (&t->rcu_node_entry == rnp->gp_tasks)
		rnp_root->gp_tasks = rnp->gp_tasks;
		if (&t->rcu_node_entry == rnp->exp_tasks)
		rnp_root->exp_tasks = rnp->exp_tasks;
		raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
		}
		rnp->gp_tasks = NULL;
		rnp->exp_tasks = NULL;
		return retval;
		}

		@@ -586,8 +619,7 @@ static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
		*/
		static int rcu_preempted_readers_exp(struct rcu_node *rnp)
		{
		return !list_empty(&rnp->blocked_tasks[2]) \|\|
		!list_empty(&rnp->blocked_tasks[3]);
		return rnp->exp_tasks != NULL;
		}

		/*
		@@ -647,12 +679,13 @@ static void rcu_report_exp_rnp(struct rcu_state rsp, struct rcu_node rnp)
		static void
		sync_rcu_preempt_exp_init(struct rcu_state rsp, struct rcu_node rnp)
		{
		int must_wait;
		int must_wait = 0;

		raw_spin_lock(&rnp->lock); /* irqs already disabled */
		list_splice_init(&rnp->blocked_tasks[0], &rnp->blocked_tasks[2]);
		list_splice_init(&rnp->blocked_tasks[1], &rnp->blocked_tasks[3]);
		must_wait = rcu_preempted_readers_exp(rnp);
		if (!list_empty(&rnp->blkd_tasks)) {
		rnp->exp_tasks = rnp->blkd_tasks.next;
		must_wait = 1;
		}
		raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
		if (!must_wait)
		rcu_report_exp_rnp(rsp, rnp);
		@@ -661,9 +694,7 @@ sync_rcu_preempt_exp_init(struct rcu_state rsp, struct rcu_node rnp)
		/*
		* Wait for an rcu-preempt grace period, but expedite it. The basic idea
		* is to invoke synchronize_sched_expedited() to push all the tasks to
		* the ->blocked_tasks[] lists, move all entries from the first set of
		* ->blocked_tasks[] lists to the second set, and finally wait for this
		* second set to drain.
		* the ->blkd_tasks lists and wait for this list to drain.
		*/
		void synchronize_rcu_expedited(void)
		{
		@@ -695,7 +726,7 @@ void synchronize_rcu_expedited(void)
		if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
		goto unlock_mb_ret; /* Others did our work for us. */

		/* force all RCU readers onto blocked_tasks[]. */
		/* force all RCU readers onto ->blkd_tasks lists. */
		synchronize_sched_expedited();

		raw_spin_lock_irqsave(&rsp->onofflock, flags);
		@@ -707,7 +738,7 @@ void synchronize_rcu_expedited(void)
		raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
		}

		/* Snapshot current state of ->blocked_tasks[] lists. */
		/* Snapshot current state of ->blkd_tasks lists. */
		rcu_for_each_leaf_node(rsp, rnp)
		sync_rcu_preempt_exp_init(rsp, rnp);
		if (NUM_RCU_NODES > 1)
		@@ -715,7 +746,7 @@ void synchronize_rcu_expedited(void)

		raw_spin_unlock_irqrestore(&rsp->onofflock, flags);

		/* Wait for snapshotted ->blocked_tasks[] lists to drain. */
		/* Wait for snapshotted ->blkd_tasks lists to drain. */
		rnp = rcu_get_root(rsp);
		wait_event(sync_rcu_preempt_exp_wq,
		sync_rcu_preempt_exp_done(rnp));

kernel/rcutree_trace.c

+4 −7

Original line number	Diff line number	Diff line
		@@ -161,7 +161,6 @@ static void print_one_rcu_state(struct seq_file m, struct rcu_state rsp)
		{
		unsigned long gpnum;
		int level = 0;
		int phase;
		struct rcu_node *rnp;

		gpnum = rsp->gpnum;
		@@ -178,13 +177,11 @@ static void print_one_rcu_state(struct seq_file m, struct rcu_state rsp)
		seq_puts(m, "\n");
		level = rnp->level;
		}
		phase = gpnum & 0x1;
		seq_printf(m, "%lx/%lx %c%c>%c%c %d:%d ^%d ",
		seq_printf(m, "%lx/%lx %c%c>%c %d:%d ^%d ",
		rnp->qsmask, rnp->qsmaskinit,
		"T."[list_empty(&rnp->blocked_tasks[phase])],
		"E."[list_empty(&rnp->blocked_tasks[phase + 2])],
		"T."[list_empty(&rnp->blocked_tasks[!phase])],
		"E."[list_empty(&rnp->blocked_tasks[!phase + 2])],
		".G"[rnp->gp_tasks != NULL],
		".E"[rnp->exp_tasks != NULL],
		".T"[!list_empty(&rnp->blkd_tasks)],
		rnp->grplo, rnp->grphi, rnp->grpnum);
		}
		seq_puts(m, "\n");

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