diff options
| -rw-r--r-- | include/trace/events/rcu.h | 1 | ||||
| -rw-r--r-- | kernel/rcu/tree.c | 72 | ||||
| -rw-r--r-- | kernel/rcu/tree.h | 2 | ||||
| -rw-r--r-- | kernel/rcu/tree_trace.c | 4 |
4 files changed, 22 insertions, 57 deletions
diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h index c78e88c..ef72c4a 100644 --- a/include/trace/events/rcu.h +++ b/include/trace/events/rcu.h @@ -661,7 +661,6 @@ TRACE_EVENT(rcu_torture_read, * Tracepoint for _rcu_barrier() execution. The string "s" describes * the _rcu_barrier phase: * "Begin": _rcu_barrier() started. - * "Check": _rcu_barrier() checking for piggybacking. * "EarlyExit": _rcu_barrier() piggybacked, thus early exit. * "Inc1": _rcu_barrier() piggyback check counter incremented. * "OfflineNoCB": _rcu_barrier() found callback on never-online CPU diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 338ea61..44245ae 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3568,10 +3568,10 @@ static void rcu_barrier_callback(struct rcu_head *rhp) struct rcu_state *rsp = rdp->rsp; if (atomic_dec_and_test(&rsp->barrier_cpu_count)) { - _rcu_barrier_trace(rsp, "LastCB", -1, rsp->n_barrier_done); + _rcu_barrier_trace(rsp, "LastCB", -1, rsp->barrier_sequence); complete(&rsp->barrier_completion); } else { - _rcu_barrier_trace(rsp, "CB", -1, rsp->n_barrier_done); + _rcu_barrier_trace(rsp, "CB", -1, rsp->barrier_sequence); } } @@ -3583,7 +3583,7 @@ static void rcu_barrier_func(void *type) struct rcu_state *rsp = type; struct rcu_data *rdp = raw_cpu_ptr(rsp->rda); - _rcu_barrier_trace(rsp, "IRQ", -1, rsp->n_barrier_done); + _rcu_barrier_trace(rsp, "IRQ", -1, rsp->barrier_sequence); atomic_inc(&rsp->barrier_cpu_count); rsp->call(&rdp->barrier_head, rcu_barrier_callback); } @@ -3596,55 +3596,24 @@ static void _rcu_barrier(struct rcu_state *rsp) { int cpu; struct rcu_data *rdp; - unsigned long snap = READ_ONCE(rsp->n_barrier_done); - unsigned long snap_done; + unsigned long s = rcu_seq_snap(&rsp->barrier_sequence); - _rcu_barrier_trace(rsp, "Begin", -1, snap); + _rcu_barrier_trace(rsp, "Begin", -1, s); /* Take mutex to serialize concurrent rcu_barrier() requests. */ mutex_lock(&rsp->barrier_mutex); - /* - * Ensure that all prior references, including to ->n_barrier_done, - * are ordered before the _rcu_barrier() machinery. - */ - smp_mb(); /* See above block comment. */ - - /* - * Recheck ->n_barrier_done to see if others did our work for us. - * This means checking ->n_barrier_done for an even-to-odd-to-even - * transition. The "if" expression below therefore rounds the old - * value up to the next even number and adds two before comparing. - */ - snap_done = rsp->n_barrier_done; - _rcu_barrier_trace(rsp, "Check", -1, snap_done); - - /* - * If the value in snap is odd, we needed to wait for the current - * rcu_barrier() to complete, then wait for the next one, in other - * words, we need the value of snap_done to be three larger than - * the value of snap. On the other hand, if the value in snap is - * even, we only had to wait for the next rcu_barrier() to complete, - * in other words, we need the value of snap_done to be only two - * greater than the value of snap. The "(snap + 3) & ~0x1" computes - * this for us (thank you, Linus!). - */ - if (ULONG_CMP_GE(snap_done, (snap + 3) & ~0x1)) { - _rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done); + /* Did someone else do our work for us? */ + if (rcu_seq_done(&rsp->barrier_sequence, s)) { + _rcu_barrier_trace(rsp, "EarlyExit", -1, rsp->barrier_sequence); smp_mb(); /* caller's subsequent code after above check. */ mutex_unlock(&rsp->barrier_mutex); return; } - /* - * Increment ->n_barrier_done to avoid duplicate work. Use - * WRITE_ONCE() to prevent the compiler from speculating - * the increment to precede the early-exit check. - */ - WRITE_ONCE(rsp->n_barrier_done, rsp->n_barrier_done + 1); - WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 1); - _rcu_barrier_trace(rsp, "Inc1", -1, rsp->n_barrier_done); - smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */ + /* Mark the start of the barrier operation. */ + rcu_seq_start(&rsp->barrier_sequence); + _rcu_barrier_trace(rsp, "Inc1", -1, rsp->barrier_sequence); /* * Initialize the count to one rather than to zero in order to @@ -3668,10 +3637,10 @@ static void _rcu_barrier(struct rcu_state *rsp) if (rcu_is_nocb_cpu(cpu)) { if (!rcu_nocb_cpu_needs_barrier(rsp, cpu)) { _rcu_barrier_trace(rsp, "OfflineNoCB", cpu, - rsp->n_barrier_done); + rsp->barrier_sequence); } else { _rcu_barrier_trace(rsp, "OnlineNoCB", cpu, - rsp->n_barrier_done); + rsp->barrier_sequence); smp_mb__before_atomic(); atomic_inc(&rsp->barrier_cpu_count); __call_rcu(&rdp->barrier_head, @@ -3679,11 +3648,11 @@ static void _rcu_barrier(struct rcu_state *rsp) } } else if (READ_ONCE(rdp->qlen)) { _rcu_barrier_trace(rsp, "OnlineQ", cpu, - rsp->n_barrier_done); + rsp->barrier_sequence); smp_call_function_single(cpu, rcu_barrier_func, rsp, 1); } else { _rcu_barrier_trace(rsp, "OnlineNQ", cpu, - rsp->n_barrier_done); + rsp->barrier_sequence); } } put_online_cpus(); @@ -3695,16 +3664,13 @@ static void _rcu_barrier(struct rcu_state *rsp) if (atomic_dec_and_test(&rsp->barrier_cpu_count)) complete(&rsp->barrier_completion); - /* Increment ->n_barrier_done to prevent duplicate work. */ - smp_mb(); /* Keep increment after above mechanism. */ - WRITE_ONCE(rsp->n_barrier_done, rsp->n_barrier_done + 1); - WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 0); - _rcu_barrier_trace(rsp, "Inc2", -1, rsp->n_barrier_done); - smp_mb(); /* Keep increment before caller's subsequent code. */ - /* Wait for all rcu_barrier_callback() callbacks to be invoked. */ wait_for_completion(&rsp->barrier_completion); + /* Mark the end of the barrier operation. */ + _rcu_barrier_trace(rsp, "Inc2", -1, rsp->barrier_sequence); + rcu_seq_end(&rsp->barrier_sequence); + /* Other rcu_barrier() invocations can now safely proceed. */ mutex_unlock(&rsp->barrier_mutex); } diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 4edc277..5c1042d 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -486,7 +486,7 @@ struct rcu_state { struct mutex barrier_mutex; /* Guards barrier fields. */ atomic_t barrier_cpu_count; /* # CPUs waiting on. */ struct completion barrier_completion; /* Wake at barrier end. */ - unsigned long n_barrier_done; /* ++ at start and end of */ + unsigned long barrier_sequence; /* ++ at start and end of */ /* _rcu_barrier(). */ /* End of fields guarded by barrier_mutex. */ diff --git a/kernel/rcu/tree_trace.c b/kernel/rcu/tree_trace.c index 36c04b4..d9982a2 100644 --- a/kernel/rcu/tree_trace.c +++ b/kernel/rcu/tree_trace.c @@ -81,9 +81,9 @@ static void r_stop(struct seq_file *m, void *v) static int show_rcubarrier(struct seq_file *m, void *v) { struct rcu_state *rsp = (struct rcu_state *)m->private; - seq_printf(m, "bcc: %d nbd: %lu\n", + seq_printf(m, "bcc: %d bseq: %lu\n", atomic_read(&rsp->barrier_cpu_count), - rsp->n_barrier_done); + rsp->barrier_sequence); return 0; } |
