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Date: Wed, 4 Mar 2020 09:24:17 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: kbuild test robot <lkp@...el.com>
Cc: kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org
Subject: Re: [rcu:dev.2020.02.29a 43/43] kernel/rcu/tasks.h:369:2: error:
implicit declaration of function 'call_rcu_tasks_generic'
On Thu, Mar 05, 2020 at 12:40:11AM +0800, kbuild test robot wrote:
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2020.02.29a
> head: 61f7110d6b78f4c84ea5d5480185740840889af7
> commit: 61f7110d6b78f4c84ea5d5480185740840889af7 [43/43] rcu-tasks: Add an RCU-tasks rude variant
> config: mips-rm200_defconfig (attached as .config)
> compiler: mipsel-linux-gcc (GCC) 5.5.0
> reproduce:
> wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> chmod +x ~/bin/make.cross
> git checkout 61f7110d6b78f4c84ea5d5480185740840889af7
> # save the attached .config to linux build tree
> GCC_VERSION=5.5.0 make.cross ARCH=mips
>
> If you fix the issue, kindly add following tag
> Reported-by: kbuild test robot <lkp@...el.com>
This is for an obsolete branch. I believe that the replacement commit
8dd788e3ab55 ("rcu-tasks: Add an RCU-tasks rude variant") fixes this.
Thanx, Paul
> All error/warnings (new ones prefixed by >>):
>
> union { typeof(x) __val; char __c[1]; } __u; \
> ^
> kernel/rcu/tasks.h:212:7: note: in expansion of macro 'READ_ONCE'
> if (!READ_ONCE(t->rcu_tasks_holdout) ||
> ^
> kernel/rcu/tasks.h:212:18: error: 'struct task_struct' has no member named 'rcu_tasks_holdout'
> if (!READ_ONCE(t->rcu_tasks_holdout) ||
> ^
> include/linux/compiler.h:287:22: note: in definition of macro '__READ_ONCE'
> __read_once_size(&(x), __u.__c, sizeof(x)); \
> ^
> kernel/rcu/tasks.h:212:7: note: in expansion of macro 'READ_ONCE'
> if (!READ_ONCE(t->rcu_tasks_holdout) ||
> ^
> kernel/rcu/tasks.h:212:18: error: 'struct task_struct' has no member named 'rcu_tasks_holdout'
> if (!READ_ONCE(t->rcu_tasks_holdout) ||
> ^
> include/linux/compiler.h:287:42: note: in definition of macro '__READ_ONCE'
> __read_once_size(&(x), __u.__c, sizeof(x)); \
> ^
> kernel/rcu/tasks.h:212:7: note: in expansion of macro 'READ_ONCE'
> if (!READ_ONCE(t->rcu_tasks_holdout) ||
> ^
> kernel/rcu/tasks.h:212:18: error: 'struct task_struct' has no member named 'rcu_tasks_holdout'
> if (!READ_ONCE(t->rcu_tasks_holdout) ||
> ^
> include/linux/compiler.h:289:30: note: in definition of macro '__READ_ONCE'
> __read_once_size_nocheck(&(x), __u.__c, sizeof(x)); \
> ^
> kernel/rcu/tasks.h:212:7: note: in expansion of macro 'READ_ONCE'
> if (!READ_ONCE(t->rcu_tasks_holdout) ||
> ^
> kernel/rcu/tasks.h:212:18: error: 'struct task_struct' has no member named 'rcu_tasks_holdout'
> if (!READ_ONCE(t->rcu_tasks_holdout) ||
> ^
> include/linux/compiler.h:289:50: note: in definition of macro '__READ_ONCE'
> __read_once_size_nocheck(&(x), __u.__c, sizeof(x)); \
> ^
> kernel/rcu/tasks.h:212:7: note: in expansion of macro 'READ_ONCE'
> if (!READ_ONCE(t->rcu_tasks_holdout) ||
> ^
> In file included from kernel/rcu/update.c:562:0:
> kernel/rcu/tasks.h:213:7: error: 'struct task_struct' has no member named 'rcu_tasks_nvcsw'
> t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) ||
> ^
> kernel/rcu/tasks.h:216:28: error: 'struct task_struct' has no member named 'rcu_tasks_idle_cpu'
> !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {
> ^
> In file included from include/linux/kernel.h:11:0,
> from kernel/rcu/update.c:21:
> kernel/rcu/tasks.h:217:15: error: 'struct task_struct' has no member named 'rcu_tasks_holdout'
> WRITE_ONCE(t->rcu_tasks_holdout, false);
> ^
> include/linux/compiler.h:310:17: note: in definition of macro 'WRITE_ONCE'
> union { typeof(x) __val; char __c[1]; } __u = \
> ^
> kernel/rcu/tasks.h:217:15: error: 'struct task_struct' has no member named 'rcu_tasks_holdout'
> WRITE_ONCE(t->rcu_tasks_holdout, false);
> ^
> include/linux/compiler.h:311:30: note: in definition of macro 'WRITE_ONCE'
> { .__val = (__force typeof(x)) (val) }; \
> ^
> kernel/rcu/tasks.h:217:15: error: 'struct task_struct' has no member named 'rcu_tasks_holdout'
> WRITE_ONCE(t->rcu_tasks_holdout, false);
> ^
> include/linux/compiler.h:312:22: note: in definition of macro 'WRITE_ONCE'
> __write_once_size(&(x), __u.__c, sizeof(x)); \
> ^
> kernel/rcu/tasks.h:217:15: error: 'struct task_struct' has no member named 'rcu_tasks_holdout'
> WRITE_ONCE(t->rcu_tasks_holdout, false);
> ^
> include/linux/compiler.h:312:42: note: in definition of macro 'WRITE_ONCE'
> __write_once_size(&(x), __u.__c, sizeof(x)); \
> ^
> In file included from kernel/rcu/update.c:562:0:
> kernel/rcu/tasks.h:218:19: error: 'struct task_struct' has no member named 'rcu_tasks_holdout_list'
> list_del_init(&t->rcu_tasks_holdout_list);
> ^
> In file included from include/linux/kernel.h:15:0,
> from kernel/rcu/update.c:21:
> kernel/rcu/tasks.h:233:5: error: 'struct task_struct' has no member named 'rcu_tasks_nvcsw'
> t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout,
> ^
> include/linux/printk.h:300:35: note: in definition of macro 'pr_alert'
> printk(KERN_ALERT pr_fmt(fmt), ##__VA_ARGS__)
> ^
> kernel/rcu/tasks.h:233:35: error: 'struct task_struct' has no member named 'rcu_tasks_holdout'
> t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout,
> ^
> include/linux/printk.h:300:35: note: in definition of macro 'pr_alert'
> printk(KERN_ALERT pr_fmt(fmt), ##__VA_ARGS__)
> ^
> kernel/rcu/tasks.h:234:5: error: 'struct task_struct' has no member named 'rcu_tasks_idle_cpu'
> t->rcu_tasks_idle_cpu, cpu);
> ^
> include/linux/printk.h:300:35: note: in definition of macro 'pr_alert'
> printk(KERN_ALERT pr_fmt(fmt), ##__VA_ARGS__)
> ^
> In file included from kernel/rcu/update.c:562:0:
> kernel/rcu/tasks.h: At top level:
> >> kernel/rcu/tasks.h:239:38: warning: 'struct rcu_tasks' declared inside parameter list
> static void rcu_tasks_wait_gp(struct rcu_tasks *rtp)
> ^
> >> kernel/rcu/tasks.h:239:38: warning: its scope is only this definition or declaration, which is probably not what you want
> kernel/rcu/tasks.h: In function 'rcu_tasks_wait_gp':
> kernel/rcu/tasks.h:271:5: error: 'struct task_struct' has no member named 'rcu_tasks_nvcsw'
> t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw);
> ^
> In file included from include/linux/kernel.h:11:0,
> from kernel/rcu/update.c:21:
> kernel/rcu/tasks.h:272:16: error: 'struct task_struct' has no member named 'rcu_tasks_holdout'
> WRITE_ONCE(t->rcu_tasks_holdout, true);
> ^
> include/linux/compiler.h:310:17: note: in definition of macro 'WRITE_ONCE'
> union { typeof(x) __val; char __c[1]; } __u = \
> ^
> kernel/rcu/tasks.h:272:16: error: 'struct task_struct' has no member named 'rcu_tasks_holdout'
> WRITE_ONCE(t->rcu_tasks_holdout, true);
> ^
> include/linux/compiler.h:311:30: note: in definition of macro 'WRITE_ONCE'
> { .__val = (__force typeof(x)) (val) }; \
> ^
> kernel/rcu/tasks.h:272:16: error: 'struct task_struct' has no member named 'rcu_tasks_holdout'
> WRITE_ONCE(t->rcu_tasks_holdout, true);
> ^
> include/linux/compiler.h:312:22: note: in definition of macro 'WRITE_ONCE'
> __write_once_size(&(x), __u.__c, sizeof(x)); \
> ^
> kernel/rcu/tasks.h:272:16: error: 'struct task_struct' has no member named 'rcu_tasks_holdout'
> WRITE_ONCE(t->rcu_tasks_holdout, true);
> ^
> include/linux/compiler.h:312:42: note: in definition of macro 'WRITE_ONCE'
> __write_once_size(&(x), __u.__c, sizeof(x)); \
> ^
> In file included from kernel/rcu/update.c:562:0:
> kernel/rcu/tasks.h:273:15: error: 'struct task_struct' has no member named 'rcu_tasks_holdout_list'
> list_add(&t->rcu_tasks_holdout_list,
> ^
> kernel/rcu/tasks.h:286:20: error: 'tasks_rcu_exit_srcu' undeclared (first use in this function)
> synchronize_srcu(&tasks_rcu_exit_srcu);
> ^
> kernel/rcu/tasks.h:286:20: note: each undeclared identifier is reported only once for each function it appears in
> In file included from include/linux/kernel.h:11:0,
> from kernel/rcu/update.c:21:
> kernel/rcu/tasks.h:313:20: error: 'rcu_task_stall_timeout' undeclared (first use in this function)
> rtst = READ_ONCE(rcu_task_stall_timeout);
> ^
> include/linux/compiler.h:285:17: note: in definition of macro '__READ_ONCE'
> union { typeof(x) __val; char __c[1]; } __u; \
> ^
> kernel/rcu/tasks.h:313:10: note: in expansion of macro 'READ_ONCE'
> rtst = READ_ONCE(rcu_task_stall_timeout);
> ^
> include/linux/kernel.h:987:51: error: 'struct task_struct' has no member named 'rcu_tasks_holdout_list'
> BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
> ^
> include/linux/compiler.h:374:9: note: in definition of macro '__compiletime_assert'
> if (!(condition)) \
> ^
> include/linux/compiler.h:394:2: note: in expansion of macro '_compiletime_assert'
> _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
> ^
> include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert'
> #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
> ^
> include/linux/kernel.h:987:2: note: in expansion of macro 'BUILD_BUG_ON_MSG'
> BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
> ^
> include/linux/kernel.h:987:20: note: in expansion of macro '__same_type'
> BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
> ^
> include/linux/list.h:493:2: note: in expansion of macro 'container_of'
> container_of(ptr, type, member)
> ^
> include/linux/list.h:504:2: note: in expansion of macro 'list_entry'
> list_entry((ptr)->next, type, member)
> ^
> include/linux/list.h:688:13: note: in expansion of macro 'list_first_entry'
> for (pos = list_first_entry(head, typeof(*pos), member), \
> ^
> kernel/rcu/tasks.h:319:3: note: in expansion of macro 'list_for_each_entry_safe'
> list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts,
> ^
> In file included from <command-line>:0:0:
> include/linux/compiler_types.h:129:35: error: 'struct task_struct' has no member named 'rcu_tasks_holdout_list'
> #define __compiler_offsetof(a, b) __builtin_offsetof(a, b)
> ^
> include/linux/stddef.h:17:32: note: in expansion of macro '__compiler_offsetof'
> #define offsetof(TYPE, MEMBER) __compiler_offsetof(TYPE, MEMBER)
> ^
> include/linux/kernel.h:990:21: note: in expansion of macro 'offsetof'
> ((type *)(__mptr - offsetof(type, member))); })
> ^
> include/linux/list.h:493:2: note: in expansion of macro 'container_of'
> container_of(ptr, type, member)
> ^
> include/linux/list.h:504:2: note: in expansion of macro 'list_entry'
> list_entry((ptr)->next, type, member)
> ^
> include/linux/list.h:688:13: note: in expansion of macro 'list_first_entry'
> for (pos = list_first_entry(head, typeof(*pos), member), \
> ^
> kernel/rcu/tasks.h:319:3: note: in expansion of macro 'list_for_each_entry_safe'
> list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts,
> --
> ^
> include/linux/list.h:537:2: note: in expansion of macro 'list_entry'
> list_entry((pos)->member.next, typeof(*(pos)), member)
> ^
> include/linux/list.h:691:20: note: in expansion of macro 'list_next_entry'
> pos = n, n = list_next_entry(n, member))
> ^
> kernel/rcu/tasks.h:319:3: note: in expansion of macro 'list_for_each_entry_safe'
> list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts,
> ^
> include/linux/kernel.h:987:51: error: 'struct task_struct' has no member named 'rcu_tasks_holdout_list'
> BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
> ^
> include/linux/compiler.h:374:9: note: in definition of macro '__compiletime_assert'
> if (!(condition)) \
> ^
> include/linux/compiler.h:394:2: note: in expansion of macro '_compiletime_assert'
> _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
> ^
> include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert'
> #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
> ^
> include/linux/kernel.h:987:2: note: in expansion of macro 'BUILD_BUG_ON_MSG'
> BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
> ^
> include/linux/kernel.h:987:20: note: in expansion of macro '__same_type'
> BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
> ^
> include/linux/list.h:493:2: note: in expansion of macro 'container_of'
> container_of(ptr, type, member)
> ^
> include/linux/list.h:537:2: note: in expansion of macro 'list_entry'
> list_entry((pos)->member.next, typeof(*(pos)), member)
> ^
> include/linux/list.h:691:20: note: in expansion of macro 'list_next_entry'
> pos = n, n = list_next_entry(n, member))
> ^
> kernel/rcu/tasks.h:319:3: note: in expansion of macro 'list_for_each_entry_safe'
> list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts,
> ^
> include/linux/list.h:537:18: error: 'struct task_struct' has no member named 'rcu_tasks_holdout_list'
> list_entry((pos)->member.next, typeof(*(pos)), member)
> ^
> include/linux/compiler.h:374:9: note: in definition of macro '__compiletime_assert'
> if (!(condition)) \
> ^
> include/linux/compiler.h:394:2: note: in expansion of macro '_compiletime_assert'
> _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
> ^
> include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert'
> #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
> ^
> include/linux/kernel.h:987:2: note: in expansion of macro 'BUILD_BUG_ON_MSG'
> BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
> ^
> include/linux/kernel.h:988:6: note: in expansion of macro '__same_type'
> !__same_type(*(ptr), void), \
> ^
> include/linux/list.h:493:2: note: in expansion of macro 'container_of'
> container_of(ptr, type, member)
> ^
> include/linux/list.h:537:2: note: in expansion of macro 'list_entry'
> list_entry((pos)->member.next, typeof(*(pos)), member)
> ^
> include/linux/list.h:691:20: note: in expansion of macro 'list_next_entry'
> pos = n, n = list_next_entry(n, member))
> ^
> kernel/rcu/tasks.h:319:3: note: in expansion of macro 'list_for_each_entry_safe'
> list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts,
> ^
> In file included from <command-line>:0:0:
> include/linux/compiler_types.h:129:35: error: 'struct task_struct' has no member named 'rcu_tasks_holdout_list'
> #define __compiler_offsetof(a, b) __builtin_offsetof(a, b)
> ^
> include/linux/stddef.h:17:32: note: in expansion of macro '__compiler_offsetof'
> #define offsetof(TYPE, MEMBER) __compiler_offsetof(TYPE, MEMBER)
> ^
> include/linux/kernel.h:990:21: note: in expansion of macro 'offsetof'
> ((type *)(__mptr - offsetof(type, member))); })
> ^
> include/linux/list.h:493:2: note: in expansion of macro 'container_of'
> container_of(ptr, type, member)
> ^
> include/linux/list.h:537:2: note: in expansion of macro 'list_entry'
> list_entry((pos)->member.next, typeof(*(pos)), member)
> ^
> include/linux/list.h:691:20: note: in expansion of macro 'list_next_entry'
> pos = n, n = list_next_entry(n, member))
> ^
> kernel/rcu/tasks.h:319:3: note: in expansion of macro 'list_for_each_entry_safe'
> list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts,
> ^
> In file included from kernel/rcu/update.c:562:0:
> kernel/rcu/tasks.h: At top level:
> kernel/rcu/tasks.h:347:1: warning: data definition has no type or storage class
> DEFINE_RCU_TASKS(rcu_tasks, rcu_tasks_wait_gp, call_rcu_tasks);
> ^
> kernel/rcu/tasks.h:347:1: error: type defaults to 'int' in declaration of 'DEFINE_RCU_TASKS' [-Werror=implicit-int]
> kernel/rcu/tasks.h:347:1: warning: parameter names (without types) in function declaration
> kernel/rcu/tasks.h: In function 'call_rcu':
> >> kernel/rcu/tasks.h:369:2: error: implicit declaration of function 'call_rcu_tasks_generic' [-Werror=implicit-function-declaration]
> call_rcu_tasks_generic(rhp, func, &rcu_tasks);
> ^
> >> kernel/rcu/tasks.h:369:37: error: 'rcu_tasks' undeclared (first use in this function)
> call_rcu_tasks_generic(rhp, func, &rcu_tasks);
> ^
> kernel/rcu/tasks.h: In function 'synchronize_rcu':
> >> kernel/rcu/tasks.h:393:2: error: implicit declaration of function 'synchronize_rcu_tasks_generic' [-Werror=implicit-function-declaration]
> synchronize_rcu_tasks_generic(&rcu_tasks);
> ^
> kernel/rcu/tasks.h:393:33: error: 'rcu_tasks' undeclared (first use in this function)
> synchronize_rcu_tasks_generic(&rcu_tasks);
> ^
> kernel/rcu/tasks.h: In function 'rcu_spawn_tasks_kthread':
> >> kernel/rcu/tasks.h:412:2: error: implicit declaration of function 'rcu_spawn_tasks_kthread_generic' [-Werror=implicit-function-declaration]
> rcu_spawn_tasks_kthread_generic(&rcu_tasks);
> ^
> kernel/rcu/tasks.h:412:35: error: 'rcu_tasks' undeclared (first use in this function)
> rcu_spawn_tasks_kthread_generic(&rcu_tasks);
> ^
> kernel/rcu/tasks.h: At top level:
> kernel/rcu/tasks.h:432:43: warning: 'struct rcu_tasks' declared inside parameter list
> static void rcu_tasks_rude_wait_gp(struct rcu_tasks *rtp)
> ^
> kernel/rcu/tasks.h:439:1: warning: data definition has no type or storage class
> DEFINE_RCU_TASKS(rcu_tasks_rude, rcu_tasks_rude_wait_gp, call_rcu_tasks_rude);
> ^
> kernel/rcu/tasks.h:439:1: error: type defaults to 'int' in declaration of 'DEFINE_RCU_TASKS' [-Werror=implicit-int]
> kernel/rcu/tasks.h:439:1: warning: parameter names (without types) in function declaration
> kernel/rcu/tasks.h: In function 'call_rcu_tasks_rude':
> >> kernel/rcu/tasks.h:461:37: error: 'rcu_tasks_rude' undeclared (first use in this function)
> call_rcu_tasks_generic(rhp, func, &rcu_tasks_rude);
> ^
> kernel/rcu/tasks.h: In function 'synchronize_rcu_tasks_rude':
> kernel/rcu/tasks.h:485:33: error: 'rcu_tasks_rude' undeclared (first use in this function)
> synchronize_rcu_tasks_generic(&rcu_tasks_rude);
> ^
> kernel/rcu/tasks.h: In function 'rcu_spawn_tasks_rude_kthread':
> kernel/rcu/tasks.h:504:35: error: 'rcu_tasks_rude' undeclared (first use in this function)
> rcu_spawn_tasks_kthread_generic(&rcu_tasks_rude);
> ^
> kernel/rcu/update.c: At top level:
> kernel/rcu/tasks.h:239:13: warning: 'rcu_tasks_wait_gp' defined but not used [-Wunused-function]
> static void rcu_tasks_wait_gp(struct rcu_tasks *rtp)
> ^
> cc1: some warnings being treated as errors
>
> vim +/call_rcu_tasks_generic +369 kernel/rcu/tasks.h
>
> 237
> 238 /* Wait for one RCU-tasks grace period. */
> > 239 static void rcu_tasks_wait_gp(struct rcu_tasks *rtp)
> 240 {
> 241 struct task_struct *g, *t;
> 242 unsigned long lastreport;
> 243 LIST_HEAD(rcu_tasks_holdouts);
> 244 int fract;
> 245
> 246 /*
> 247 * Wait for all pre-existing t->on_rq and t->nvcsw transitions
> 248 * to complete. Invoking synchronize_rcu() suffices because all
> 249 * these transitions occur with interrupts disabled. Without this
> 250 * synchronize_rcu(), a read-side critical section that started
> 251 * before the grace period might be incorrectly seen as having
> 252 * started after the grace period.
> 253 *
> 254 * This synchronize_rcu() also dispenses with the need for a
> 255 * memory barrier on the first store to t->rcu_tasks_holdout,
> 256 * as it forces the store to happen after the beginning of the
> 257 * grace period.
> 258 */
> 259 synchronize_rcu();
> 260
> 261 /*
> 262 * There were callbacks, so we need to wait for an RCU-tasks
> 263 * grace period. Start off by scanning the task list for tasks
> 264 * that are not already voluntarily blocked. Mark these tasks
> 265 * and make a list of them in rcu_tasks_holdouts.
> 266 */
> 267 rcu_read_lock();
> 268 for_each_process_thread(g, t) {
> 269 if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t)) {
> 270 get_task_struct(t);
> 271 t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw);
> 272 WRITE_ONCE(t->rcu_tasks_holdout, true);
> 273 list_add(&t->rcu_tasks_holdout_list,
> 274 &rcu_tasks_holdouts);
> 275 }
> 276 }
> 277 rcu_read_unlock();
> 278
> 279 /*
> 280 * Wait for tasks that are in the process of exiting. This
> 281 * does only part of the job, ensuring that all tasks that were
> 282 * previously exiting reach the point where they have disabled
> 283 * preemption, allowing the later synchronize_rcu() to finish
> 284 * the job.
> 285 */
> 286 synchronize_srcu(&tasks_rcu_exit_srcu);
> 287
> 288 /*
> 289 * Each pass through the following loop scans the list of holdout
> 290 * tasks, removing any that are no longer holdouts. When the list
> 291 * is empty, we are done.
> 292 */
> 293 lastreport = jiffies;
> 294
> 295 /* Start off with HZ/10 wait and slowly back off to 1 HZ wait. */
> 296 fract = 10;
> 297
> 298 for (;;) {
> 299 bool firstreport;
> 300 bool needreport;
> 301 int rtst;
> 302 struct task_struct *t1;
> 303
> 304 if (list_empty(&rcu_tasks_holdouts))
> 305 break;
> 306
> 307 /* Slowly back off waiting for holdouts */
> 308 schedule_timeout_interruptible(HZ/fract);
> 309
> 310 if (fract > 1)
> 311 fract--;
> 312
> 313 rtst = READ_ONCE(rcu_task_stall_timeout);
> 314 needreport = rtst > 0 && time_after(jiffies, lastreport + rtst);
> 315 if (needreport)
> 316 lastreport = jiffies;
> 317 firstreport = true;
> 318 WARN_ON(signal_pending(current));
> 319 list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts,
> 320 rcu_tasks_holdout_list) {
> 321 check_holdout_task(t, needreport, &firstreport);
> 322 cond_resched();
> 323 }
> 324 }
> 325
> 326 /*
> 327 * Because ->on_rq and ->nvcsw are not guaranteed to have a full
> 328 * memory barriers prior to them in the schedule() path, memory
> 329 * reordering on other CPUs could cause their RCU-tasks read-side
> 330 * critical sections to extend past the end of the grace period.
> 331 * However, because these ->nvcsw updates are carried out with
> 332 * interrupts disabled, we can use synchronize_rcu() to force the
> 333 * needed ordering on all such CPUs.
> 334 *
> 335 * This synchronize_rcu() also confines all ->rcu_tasks_holdout
> 336 * accesses to be within the grace period, avoiding the need for
> 337 * memory barriers for ->rcu_tasks_holdout accesses.
> 338 *
> 339 * In addition, this synchronize_rcu() waits for exiting tasks
> 340 * to complete their final preempt_disable() region of execution,
> 341 * cleaning up after the synchronize_srcu() above.
> 342 */
> 343 synchronize_rcu();
> 344 }
> 345
> 346 void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func);
> 347 DEFINE_RCU_TASKS(rcu_tasks, rcu_tasks_wait_gp, call_rcu_tasks);
> 348
> 349 /**
> 350 * call_rcu_tasks() - Queue an RCU for invocation task-based grace period
> 351 * @rhp: structure to be used for queueing the RCU updates.
> 352 * @func: actual callback function to be invoked after the grace period
> 353 *
> 354 * The callback function will be invoked some time after a full grace
> 355 * period elapses, in other words after all currently executing RCU
> 356 * read-side critical sections have completed. call_rcu_tasks() assumes
> 357 * that the read-side critical sections end at a voluntary context
> 358 * switch (not a preemption!), cond_resched_rcu_qs(), entry into idle,
> 359 * or transition to usermode execution. As such, there are no read-side
> 360 * primitives analogous to rcu_read_lock() and rcu_read_unlock() because
> 361 * this primitive is intended to determine that all tasks have passed
> 362 * through a safe state, not so much for data-strcuture synchronization.
> 363 *
> 364 * See the description of call_rcu() for more detailed information on
> 365 * memory ordering guarantees.
> 366 */
> 367 void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func)
> 368 {
> > 369 call_rcu_tasks_generic(rhp, func, &rcu_tasks);
> 370 }
> 371 EXPORT_SYMBOL_GPL(call_rcu_tasks);
> 372
> 373 /**
> 374 * synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed.
> 375 *
> 376 * Control will return to the caller some time after a full rcu-tasks
> 377 * grace period has elapsed, in other words after all currently
> 378 * executing rcu-tasks read-side critical sections have elapsed. These
> 379 * read-side critical sections are delimited by calls to schedule(),
> 380 * cond_resched_tasks_rcu_qs(), idle execution, userspace execution, calls
> 381 * to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched().
> 382 *
> 383 * This is a very specialized primitive, intended only for a few uses in
> 384 * tracing and other situations requiring manipulation of function
> 385 * preambles and profiling hooks. The synchronize_rcu_tasks() function
> 386 * is not (yet) intended for heavy use from multiple CPUs.
> 387 *
> 388 * See the description of synchronize_rcu() for more detailed information
> 389 * on memory ordering guarantees.
> 390 */
> 391 void synchronize_rcu_tasks(void)
> 392 {
> > 393 synchronize_rcu_tasks_generic(&rcu_tasks);
> 394 }
> 395 EXPORT_SYMBOL_GPL(synchronize_rcu_tasks);
> 396
> 397 /**
> 398 * rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks.
> 399 *
> 400 * Although the current implementation is guaranteed to wait, it is not
> 401 * obligated to, for example, if there are no pending callbacks.
> 402 */
> 403 void rcu_barrier_tasks(void)
> 404 {
> 405 /* There is only one callback queue, so this is easy. ;-) */
> 406 synchronize_rcu_tasks();
> 407 }
> 408 EXPORT_SYMBOL_GPL(rcu_barrier_tasks);
> 409
> 410 static int __init rcu_spawn_tasks_kthread(void)
> 411 {
> > 412 rcu_spawn_tasks_kthread_generic(&rcu_tasks);
> 413 return 0;
> 414 }
> 415 core_initcall(rcu_spawn_tasks_kthread);
> 416
> 417 ////////////////////////////////////////////////////////////////////////
> 418 //
> 419 // "Rude" variant of Tasks RCU, inspired by Steve Rostedt's trick of
> 420 // passing an empty function to schedule_on_each_cpu(). This approach
> 421 // provides an asynchronous call_rcu_rude() API and batching of concurrent
> 422 // calls to the synchronous synchronize_rcu_rude() API. This sends IPIs
> 423 // far and wide and induces otherwise unnecessary context switches on all
> 424 // online CPUs, whether online or not.
> 425
> 426 // Empty function to allow workqueues to force a context switch.
> 427 static void rcu_tasks_be_rude(struct work_struct *work)
> 428 {
> 429 }
> 430
> 431 // Wait for one rude RCU-tasks grace period.
> 432 static void rcu_tasks_rude_wait_gp(struct rcu_tasks *rtp)
> 433 {
> 434 schedule_on_each_cpu(rcu_tasks_be_rude);
> 435 }
> 436 EXPORT_SYMBOL_GPL(rcu_tasks_rude_wait_gp);
> 437
> 438 void call_rcu_tasks_rude(struct rcu_head *rhp, rcu_callback_t func);
> 439 DEFINE_RCU_TASKS(rcu_tasks_rude, rcu_tasks_rude_wait_gp, call_rcu_tasks_rude);
> 440
> 441 /**
> 442 * call_rcu_tasks_rude() - Queue a callback rude task-based grace period
> 443 * @rhp: structure to be used for queueing the RCU updates.
> 444 * @func: actual callback function to be invoked after the grace period
> 445 *
> 446 * The callback function will be invoked some time after a full grace
> 447 * period elapses, in other words after all currently executing RCU
> 448 * read-side critical sections have completed. call_rcu_tasks_rude()
> 449 * assumes that the read-side critical sections end at context switch,
> 450 * cond_resched_rcu_qs(), or transition to usermode execution. As such,
> 451 * there are no read-side primitives analogous to rcu_read_lock() and
> 452 * rcu_read_unlock() because this primitive is intended to determine
> 453 * that all tasks have passed through a safe state, not so much for
> 454 * data-strcuture synchronization.
> 455 *
> 456 * See the description of call_rcu() for more detailed information on
> 457 * memory ordering guarantees.
> 458 */
> 459 void call_rcu_tasks_rude(struct rcu_head *rhp, rcu_callback_t func)
> 460 {
> > 461 call_rcu_tasks_generic(rhp, func, &rcu_tasks_rude);
> 462 }
> 463 EXPORT_SYMBOL_GPL(call_rcu_tasks_rude);
> 464
>
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
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