Messages in this thread | | | Date | Thu, 25 Apr 2019 18:40:54 +0200 | From | Oleg Nesterov <> | Subject | [PATCH 0/1] rcu/sync: simplify the state machine |
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Let me finally try to close the gestalt ;)
This version doesn't add the new features yet, and it doesn't remove the "must die" rcu_sync_enter_start(). But with this patch we are ready, just I think that this should come as a separate change.
To simplify the review, see the the most important parts of the code with the patch applied below.
Oleg. -------------------------------------------------------------------------------
struct rcu_sync { int gp_state; int gp_count; wait_queue_head_t gp_wait;
struct rcu_head cb_head; };
enum { GP_IDLE = 0, GP_ENTER, GP_PASSED, GP_EXIT, GP_REPLAY };
#define rss_lock gp_wait.lock
static void rcu_sync_call(struct rcu_sync *rsp) { call_rcu(&rsp->cb_head, rcu_sync_func); }
static void rcu_sync_func(struct rcu_head *rcu) { struct rcu_sync *rsp = container_of(rcu, struct rcu_sync, cb_head); unsigned long flags;
WARN_ON_ONCE(rsp->gp_state == GP_IDLE); WARN_ON_ONCE(rsp->gp_state == GP_PASSED);
spin_lock_irqsave(&rsp->rss_lock, flags); if (rsp->gp_count) { /* * We're at least a GP after the GP_IDLE->GP_ENTER transition. */ rsp->gp_state = GP_PASSED; wake_up_locked(&rsp->gp_wait); } else if (rsp->gp_state == GP_REPLAY) { /* * A new rcu_sync_exit() has happened; requeue the callback to * catch a later GP. */ rsp->gp_state = GP_EXIT; rcu_sync_call(rsp); } else { /* * We're at least a GP after the last rcu_sync_exit(); eveybody * will now have observed the write side critical section. * Let 'em rip!. */ rsp->gp_state = GP_IDLE; } spin_unlock_irqrestore(&rsp->rss_lock, flags); }
void rcu_sync_enter(struct rcu_sync *rsp) { int gp_state;
spin_lock_irq(&rsp->rss_lock); gp_state = rsp->gp_state; if (gp_state == GP_IDLE) { rsp->gp_state = GP_ENTER; WARN_ON_ONCE(rsp->gp_count); /* * Note that we could simply do rcu_sync_call(rsp) here and * avoid the "if (gp_state == GP_IDLE)" block below. * * However, synchronize_rcu() can be faster if rcu_expedited * or rcu_blocking_is_gp() is true. * * Another reason is that we can't wait for rcu callback if * we are called at early boot time but this shouldn't happen. */ } rsp->gp_count++; spin_unlock_irq(&rsp->rss_lock);
if (gp_state == GP_IDLE) { /* * See the comment above, this simply does the "synchronous" * call_rcu(rcu_sync_func) which does GP_ENTER -> GP_PASSED. */ synchronize_rcu(); rcu_sync_func(&rsp->cb_head); /* Not really needed, wait_event() would see GP_PASSED. */ return; }
wait_event(rsp->gp_wait, rsp->gp_state >= GP_PASSED); }
void rcu_sync_exit(struct rcu_sync *rsp) { WARN_ON_ONCE(rsp->gp_state == GP_IDLE); WARN_ON_ONCE(rsp->gp_count == 0);
spin_lock_irq(&rsp->rss_lock); if (!--rsp->gp_count) { if (rsp->gp_state == GP_PASSED) { rsp->gp_state = GP_EXIT; rcu_sync_call(rsp); } else if (rsp->gp_state == GP_EXIT) { rsp->gp_state = GP_REPLAY; } } spin_unlock_irq(&rsp->rss_lock); }
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