tasks: Add a count of task RCU users

Add a count of the number of RCU users (currently 1) of the task struct so that we can later add the scheduler case and get rid of the very subtle task_rcu_dereference(), and just use rcu_dereference(). As suggested by Oleg have the count overlap rcu_head so that no additional space in task_struct is required.

Eric W. Biederman committed 7 years ago

Commit 3fbd7ee1 parent 42fd8ba4 files · +14 −6Browse files

Unified · Split

4 files

include/linux/sched.h +4 −1
include/linux/sched/task.h +1 −0
kernel/exit.c +6 −1
kernel/fork.c +3 −4

include/linux/sched.h+4−1

@@ -1147,7 +1147,10 @@ struct task_struct { · 1146 unmodified lines
1147	1147
1148	1148	struct tlbflush_unmap_batch tlb_ubc;
1149	1149
1150		− struct rcu_head rcu;
	1150	+ union {
	1151	+ refcount_t rcu_users;
	1152	+ struct rcu_head rcu;
	1153	+ };
1151	1154
1152	1155	/* Cache last used pipe for splice(): */
1153	1156	struct pipe_inode_info *splice_pipe;

include/linux/sched/task.h+1−0

@@ -120,6 +120,7 @@ static inline void put_task_struct(struct task_struct *t) · 119 unmodified lines
120	120	}
121	121
122	122	struct task_struct task_rcu_dereference(struct task_struct *ptask);
	123	+void put_task_struct_rcu_user(struct task_struct *task);
123	124
124	125	#ifdef CONFIG_ARCH_WANTS_DYNAMIC_TASK_STRUCT
125	126	extern int arch_task_struct_size __read_mostly;

kernel/exit.c+6−1

@@ -182,6 +182,11 @@ static void delayed_put_task_struct(struct rcu_head *rhp) · 181 unmodified lines
182	182	put_task_struct(tsk);
183	183	}
184	184
	185	+void put_task_struct_rcu_user(struct task_struct *task)
	186	+{
	187	+ if (refcount_dec_and_test(&task->rcu_users))
	188	+ call_rcu(&task->rcu, delayed_put_task_struct);
	189	+}
185	190
186	191	void release_task(struct task_struct *p)
187	192	{
@@ -222,7 +227,7 @@ repeat: · 34 unmodified lines
222	227
223	228	write_unlock_irq(&tasklist_lock);
224	229	release_thread(p);
225		− call_rcu(&p->rcu, delayed_put_task_struct);
	230	+ put_task_struct_rcu_user(p);
226	231
227	232	p = leader;
228	233	if (unlikely(zap_leader))

kernel/fork.c+3−4

@@ -902,10 +902,9 @@ static struct task_struct dup_task_struct(struct task_struct orig, int node) · 901 unmodified lines
902	902	if (orig->cpus_ptr == &orig->cpus_mask)
903	903	tsk->cpus_ptr = &tsk->cpus_mask;
904	904
905		− /*
906		− * One for us, one for whoever does the "release_task()" (usually
907		− * parent)
908		− */
	905	+ /* One for the user space visible state that goes away when reaped. */
	906	+ refcount_set(&tsk->rcu_users, 1);
	907	+ /* One for the rcu users, and one for the scheduler */
909	908	refcount_set(&tsk->usage, 2);
910	909	#ifdef CONFIG_BLK_DEV_IO_TRACE
911	910	tsk->btrace_seq = 0;

tasks: Add a count of task RCU users

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