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Merge branch 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull core fixes from Ingo Molnar: "The tree contains two RCU fixes and a compiler quirk comment fix" * 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: rcu: Make rcu_barrier() understand about missing rcuo kthreads compiler/gcc4+: Remove inaccurate comment about 'asm goto' miscompiles rcu: More on deadlock between CPU hotplug and expedited grace periods
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commit
aea4869f68
@ -71,7 +71,6 @@
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* http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
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*
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* Work it around via a compiler barrier quirk suggested by Jakub Jelinek.
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* Fixed in GCC 4.8.2 and later versions.
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*
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* (asm goto is automatically volatile - the naming reflects this.)
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*/
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@ -53,7 +53,6 @@
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* http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
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*
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* Work it around via a compiler barrier quirk suggested by Jakub Jelinek.
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* Fixed in GCC 4.8.2 and later versions.
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*
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* (asm goto is automatically volatile - the naming reflects this.)
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*/
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@ -660,18 +660,18 @@ TRACE_EVENT(rcu_torture_read,
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/*
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* Tracepoint for _rcu_barrier() execution. The string "s" describes
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* the _rcu_barrier phase:
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* "Begin": rcu_barrier_callback() started.
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* "Check": rcu_barrier_callback() checking for piggybacking.
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* "EarlyExit": rcu_barrier_callback() piggybacked, thus early exit.
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* "Inc1": rcu_barrier_callback() piggyback check counter incremented.
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* "Offline": rcu_barrier_callback() found offline CPU
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* "OnlineNoCB": rcu_barrier_callback() found online no-CBs CPU.
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* "OnlineQ": rcu_barrier_callback() found online CPU with callbacks.
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* "OnlineNQ": rcu_barrier_callback() found online CPU, no callbacks.
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* "Begin": _rcu_barrier() started.
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* "Check": _rcu_barrier() checking for piggybacking.
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* "EarlyExit": _rcu_barrier() piggybacked, thus early exit.
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* "Inc1": _rcu_barrier() piggyback check counter incremented.
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* "OfflineNoCB": _rcu_barrier() found callback on never-online CPU
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* "OnlineNoCB": _rcu_barrier() found online no-CBs CPU.
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* "OnlineQ": _rcu_barrier() found online CPU with callbacks.
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* "OnlineNQ": _rcu_barrier() found online CPU, no callbacks.
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* "IRQ": An rcu_barrier_callback() callback posted on remote CPU.
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* "CB": An rcu_barrier_callback() invoked a callback, not the last.
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* "LastCB": An rcu_barrier_callback() invoked the last callback.
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* "Inc2": rcu_barrier_callback() piggyback check counter incremented.
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* "Inc2": _rcu_barrier() piggyback check counter incremented.
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* The "cpu" argument is the CPU or -1 if meaningless, the "cnt" argument
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* is the count of remaining callbacks, and "done" is the piggybacking count.
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*/
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14
kernel/cpu.c
14
kernel/cpu.c
@ -64,6 +64,8 @@ static struct {
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* an ongoing cpu hotplug operation.
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*/
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int refcount;
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/* And allows lockless put_online_cpus(). */
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atomic_t puts_pending;
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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struct lockdep_map dep_map;
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@ -113,7 +115,11 @@ void put_online_cpus(void)
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{
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if (cpu_hotplug.active_writer == current)
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return;
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mutex_lock(&cpu_hotplug.lock);
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if (!mutex_trylock(&cpu_hotplug.lock)) {
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atomic_inc(&cpu_hotplug.puts_pending);
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cpuhp_lock_release();
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return;
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}
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if (WARN_ON(!cpu_hotplug.refcount))
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cpu_hotplug.refcount++; /* try to fix things up */
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@ -155,6 +161,12 @@ void cpu_hotplug_begin(void)
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cpuhp_lock_acquire();
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for (;;) {
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mutex_lock(&cpu_hotplug.lock);
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if (atomic_read(&cpu_hotplug.puts_pending)) {
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int delta;
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delta = atomic_xchg(&cpu_hotplug.puts_pending, 0);
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cpu_hotplug.refcount -= delta;
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}
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if (likely(!cpu_hotplug.refcount))
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break;
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__set_current_state(TASK_UNINTERRUPTIBLE);
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@ -3299,11 +3299,16 @@ static void _rcu_barrier(struct rcu_state *rsp)
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continue;
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rdp = per_cpu_ptr(rsp->rda, cpu);
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if (rcu_is_nocb_cpu(cpu)) {
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_rcu_barrier_trace(rsp, "OnlineNoCB", cpu,
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rsp->n_barrier_done);
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atomic_inc(&rsp->barrier_cpu_count);
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__call_rcu(&rdp->barrier_head, rcu_barrier_callback,
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rsp, cpu, 0);
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if (!rcu_nocb_cpu_needs_barrier(rsp, cpu)) {
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_rcu_barrier_trace(rsp, "OfflineNoCB", cpu,
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rsp->n_barrier_done);
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} else {
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_rcu_barrier_trace(rsp, "OnlineNoCB", cpu,
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rsp->n_barrier_done);
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atomic_inc(&rsp->barrier_cpu_count);
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__call_rcu(&rdp->barrier_head,
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rcu_barrier_callback, rsp, cpu, 0);
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}
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} else if (ACCESS_ONCE(rdp->qlen)) {
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_rcu_barrier_trace(rsp, "OnlineQ", cpu,
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rsp->n_barrier_done);
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@ -587,6 +587,7 @@ static void print_cpu_stall_info(struct rcu_state *rsp, int cpu);
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static void print_cpu_stall_info_end(void);
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static void zero_cpu_stall_ticks(struct rcu_data *rdp);
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static void increment_cpu_stall_ticks(void);
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static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu);
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static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq);
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static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp);
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static void rcu_init_one_nocb(struct rcu_node *rnp);
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@ -2049,6 +2049,33 @@ static void wake_nocb_leader(struct rcu_data *rdp, bool force)
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}
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}
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/*
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* Does the specified CPU need an RCU callback for the specified flavor
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* of rcu_barrier()?
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*/
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static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
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{
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struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
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struct rcu_head *rhp;
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/* No-CBs CPUs might have callbacks on any of three lists. */
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rhp = ACCESS_ONCE(rdp->nocb_head);
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if (!rhp)
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rhp = ACCESS_ONCE(rdp->nocb_gp_head);
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if (!rhp)
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rhp = ACCESS_ONCE(rdp->nocb_follower_head);
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/* Having no rcuo kthread but CBs after scheduler starts is bad! */
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if (!ACCESS_ONCE(rdp->nocb_kthread) && rhp) {
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/* RCU callback enqueued before CPU first came online??? */
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pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n",
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cpu, rhp->func);
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WARN_ON_ONCE(1);
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}
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return !!rhp;
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}
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/*
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* Enqueue the specified string of rcu_head structures onto the specified
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* CPU's no-CBs lists. The CPU is specified by rdp, the head of the
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@ -2642,6 +2669,12 @@ static bool init_nocb_callback_list(struct rcu_data *rdp)
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#else /* #ifdef CONFIG_RCU_NOCB_CPU */
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static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
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{
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WARN_ON_ONCE(1); /* Should be dead code. */
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return false;
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}
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static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
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{
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}
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