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Commit ab4720ec76b756e1f8705e207a7b392b0453afd6

Authored by Dipankar Sarma
Committed by Linus Torvalds
1 parent 85b8724249
Exists in master and in 7 other branches imx_3.0.35_4.1.0, imx_3.10.17_1.0.1_ga, imx_3.10.53_1.1.0_ga, imx_3.14.28_1.0.0_ga, smarc-imx_3.10.53_1.1.0_ga, smarc-imx_3.14.28_1.0.0_ga, smarc-l5.0.0_1.0.0-ga

[PATCH] add rcu_barrier() synchronization point 

This introduces a new interface - rcu_barrier() which waits until all
the RCUs queued until this call have been completed.

Reiser4 needs this, because we do more than just freeing memory object
in our RCU callback: we also remove it from the list hanging off
super-block.  This means, that before freeing reiser4-specific portion
of super-block (during umount) we have to wait until all pending RCU
callbacks are executed.

The only change of reiser4 made to the original patch, is exporting of
rcu_barrier().

Cc: Hans Reiser <reiser@namesys.com>
Cc: Vladimir V. Saveliev <vs@namesys.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

Showing 2 changed files with 43 additions and 0 deletions Side-by-side Diff

include/linux/rcupdate.h
Diff comments   View file @ ab4720e
... ... @@ -100,6 +100,7 @@
100 100 struct rcu_head *donelist;
101 101 struct rcu_head **donetail;
102 102 int cpu;
  103 + struct rcu_head barrier;
103 104 };
104 105  
105 106 DECLARE_PER_CPU(struct rcu_data, rcu_data);
... ... @@ -285,6 +286,7 @@
285 286 extern __deprecated_for_modules void synchronize_kernel(void);
286 287 extern void synchronize_rcu(void);
287 288 void synchronize_idle(void);
  289 +extern void rcu_barrier(void);
288 290  
289 291 #endif /* __KERNEL__ */
290 292 #endif /* __LINUX_RCUPDATE_H */
... ... @@ -116,6 +116,10 @@
116 116 local_irq_restore(flags);
117 117 }
118 118  
  119 +static atomic_t rcu_barrier_cpu_count;
  120 +static struct semaphore rcu_barrier_sema;
  121 +static struct completion rcu_barrier_completion;
  122 +
119 123 /**
120 124 * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
121 125 * @head: structure to be used for queueing the RCU updates.
122 126  
... ... @@ -162,7 +166,43 @@
162 166 return rcu_ctrlblk.completed;
163 167 }
164 168  
  169 +static void rcu_barrier_callback(struct rcu_head *notused)
  170 +{
  171 + if (atomic_dec_and_test(&rcu_barrier_cpu_count))
  172 + complete(&rcu_barrier_completion);
  173 +}
  174 +
165 175 /*
  176 + * Called with preemption disabled, and from cross-cpu IRQ context.
  177 + */
  178 +static void rcu_barrier_func(void *notused)
  179 +{
  180 + int cpu = smp_processor_id();
  181 + struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
  182 + struct rcu_head *head;
  183 +
  184 + head = &rdp->barrier;
  185 + atomic_inc(&rcu_barrier_cpu_count);
  186 + call_rcu(head, rcu_barrier_callback);
  187 +}
  188 +
  189 +/**
  190 + * rcu_barrier - Wait until all the in-flight RCUs are complete.
  191 + */
  192 +void rcu_barrier(void)
  193 +{
  194 + BUG_ON(in_interrupt());
  195 + /* Take cpucontrol semaphore to protect against CPU hotplug */
  196 + down(&rcu_barrier_sema);
  197 + init_completion(&rcu_barrier_completion);
  198 + atomic_set(&rcu_barrier_cpu_count, 0);
  199 + on_each_cpu(rcu_barrier_func, NULL, 0, 1);
  200 + wait_for_completion(&rcu_barrier_completion);
  201 + up(&rcu_barrier_sema);
  202 +}
  203 +EXPORT_SYMBOL_GPL(rcu_barrier);
  204 +
  205 +/*
166 206 * Invoke the completed RCU callbacks. They are expected to be in
167 207 * a per-cpu list.
168 208 */
... ... @@ -457,6 +497,7 @@
457 497 */
458 498 void __init rcu_init(void)
459 499 {
  500 + sema_init(&rcu_barrier_sema, 1);
460 501 rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE,
461 502 (void *)(long)smp_processor_id());
462 503 /* Register notifier for non-boot CPUs */