diff options
Diffstat (limited to 'rcu-Make-rcu_barrier-understand-about-missing-rcuo-k.patch')
| -rw-r--r-- | rcu-Make-rcu_barrier-understand-about-missing-rcuo-k.patch | 177 |
1 files changed, 0 insertions, 177 deletions
diff --git a/rcu-Make-rcu_barrier-understand-about-missing-rcuo-k.patch b/rcu-Make-rcu_barrier-understand-about-missing-rcuo-k.patch deleted file mode 100644 index ca3592e53..000000000 --- a/rcu-Make-rcu_barrier-understand-about-missing-rcuo-k.patch +++ /dev/null @@ -1,177 +0,0 @@ -From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> -Date: Mon, 27 Oct 2014 09:15:54 -0700 -Subject: [PATCH] rcu: Make rcu_barrier() understand about missing rcuo - kthreads - -Commit 35ce7f29a44a (rcu: Create rcuo kthreads only for onlined CPUs) -avoids creating rcuo kthreads for CPUs that never come online. This -fixes a bug in many instances of firmware: Instead of lying about their -age, these systems instead lie about the number of CPUs that they have. -Before commit 35ce7f29a44a, this could result in huge numbers of useless -rcuo kthreads being created. - -It appears that experience indicates that I should have told the -people suffering from this problem to fix their broken firmware, but -I instead produced what turned out to be a partial fix. The missing -piece supplied by this commit makes sure that rcu_barrier() knows not to -post callbacks for no-CBs CPUs that have not yet come online, because -otherwise rcu_barrier() will hang on systems having firmware that lies -about the number of CPUs. - -It is tempting to simply have rcu_barrier() refuse to post a callback on -any no-CBs CPU that does not have an rcuo kthread. This unfortunately -does not work because rcu_barrier() is required to wait for all pending -callbacks. It is therefore required to wait even for those callbacks -that cannot possibly be invoked. Even if doing so hangs the system. - -Given that posting a callback to a no-CBs CPU that does not yet have an -rcuo kthread can hang rcu_barrier(), It is tempting to report an error -in this case. Unfortunately, this will result in false positives at -boot time, when it is perfectly legal to post callbacks to the boot CPU -before the scheduler has started, in other words, before it is legal -to invoke rcu_barrier(). - -So this commit instead has rcu_barrier() avoid posting callbacks to -CPUs having neither rcuo kthread nor pending callbacks, and has it -complain bitterly if it finds CPUs having no rcuo kthread but some -pending callbacks. And when rcu_barrier() does find CPUs having no rcuo -kthread but pending callbacks, as noted earlier, it has no choice but -to hang indefinitely. - -Reported-by: Yanko Kaneti <yaneti@declera.com> -Reported-by: Jay Vosburgh <jay.vosburgh@canonical.com> -Reported-by: Meelis Roos <mroos@linux.ee> -Reported-by: Eric B Munson <emunson@akamai.com> -Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> -Tested-by: Eric B Munson <emunson@akamai.com> ---- - include/trace/events/rcu.h | 18 +++++++++--------- - kernel/rcu/tree.c | 15 ++++++++++----- - kernel/rcu/tree.h | 1 + - kernel/rcu/tree_plugin.h | 33 +++++++++++++++++++++++++++++++++ - 4 files changed, 53 insertions(+), 14 deletions(-) - -diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h -index 9b56f37148cf..e335e7d8c6c2 100644 ---- a/include/trace/events/rcu.h -+++ b/include/trace/events/rcu.h -@@ -660,18 +660,18 @@ TRACE_EVENT(rcu_torture_read, - /* - * Tracepoint for _rcu_barrier() execution. The string "s" describes - * the _rcu_barrier phase: -- * "Begin": rcu_barrier_callback() started. -- * "Check": rcu_barrier_callback() checking for piggybacking. -- * "EarlyExit": rcu_barrier_callback() piggybacked, thus early exit. -- * "Inc1": rcu_barrier_callback() piggyback check counter incremented. -- * "Offline": rcu_barrier_callback() found offline CPU -- * "OnlineNoCB": rcu_barrier_callback() found online no-CBs CPU. -- * "OnlineQ": rcu_barrier_callback() found online CPU with callbacks. -- * "OnlineNQ": rcu_barrier_callback() found online CPU, no callbacks. -+ * "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 -+ * "OnlineNoCB": _rcu_barrier() found online no-CBs CPU. -+ * "OnlineQ": _rcu_barrier() found online CPU with callbacks. -+ * "OnlineNQ": _rcu_barrier() found online CPU, no callbacks. - * "IRQ": An rcu_barrier_callback() callback posted on remote CPU. - * "CB": An rcu_barrier_callback() invoked a callback, not the last. - * "LastCB": An rcu_barrier_callback() invoked the last callback. -- * "Inc2": rcu_barrier_callback() piggyback check counter incremented. -+ * "Inc2": _rcu_barrier() piggyback check counter incremented. - * The "cpu" argument is the CPU or -1 if meaningless, the "cnt" argument - * is the count of remaining callbacks, and "done" is the piggybacking count. - */ -diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c -index 133e47223095..9815447d22e0 100644 ---- a/kernel/rcu/tree.c -+++ b/kernel/rcu/tree.c -@@ -3299,11 +3299,16 @@ static void _rcu_barrier(struct rcu_state *rsp) - continue; - rdp = per_cpu_ptr(rsp->rda, cpu); - if (rcu_is_nocb_cpu(cpu)) { -- _rcu_barrier_trace(rsp, "OnlineNoCB", cpu, -- rsp->n_barrier_done); -- atomic_inc(&rsp->barrier_cpu_count); -- __call_rcu(&rdp->barrier_head, rcu_barrier_callback, -- rsp, cpu, 0); -+ if (!rcu_nocb_cpu_needs_barrier(rsp, cpu)) { -+ _rcu_barrier_trace(rsp, "OfflineNoCB", cpu, -+ rsp->n_barrier_done); -+ } else { -+ _rcu_barrier_trace(rsp, "OnlineNoCB", cpu, -+ rsp->n_barrier_done); -+ atomic_inc(&rsp->barrier_cpu_count); -+ __call_rcu(&rdp->barrier_head, -+ rcu_barrier_callback, rsp, cpu, 0); -+ } - } else if (ACCESS_ONCE(rdp->qlen)) { - _rcu_barrier_trace(rsp, "OnlineQ", cpu, - rsp->n_barrier_done); -diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h -index d03764652d91..bbdc45d8d74f 100644 ---- a/kernel/rcu/tree.h -+++ b/kernel/rcu/tree.h -@@ -587,6 +587,7 @@ static void print_cpu_stall_info(struct rcu_state *rsp, int cpu); - static void print_cpu_stall_info_end(void); - static void zero_cpu_stall_ticks(struct rcu_data *rdp); - static void increment_cpu_stall_ticks(void); -+static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu); - static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq); - static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp); - static void rcu_init_one_nocb(struct rcu_node *rnp); -diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h -index 387dd4599344..c1d7f27bd38f 100644 ---- a/kernel/rcu/tree_plugin.h -+++ b/kernel/rcu/tree_plugin.h -@@ -2050,6 +2050,33 @@ static void wake_nocb_leader(struct rcu_data *rdp, bool force) - } - - /* -+ * Does the specified CPU need an RCU callback for the specified flavor -+ * of rcu_barrier()? -+ */ -+static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu) -+{ -+ struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); -+ struct rcu_head *rhp; -+ -+ /* No-CBs CPUs might have callbacks on any of three lists. */ -+ rhp = ACCESS_ONCE(rdp->nocb_head); -+ if (!rhp) -+ rhp = ACCESS_ONCE(rdp->nocb_gp_head); -+ if (!rhp) -+ rhp = ACCESS_ONCE(rdp->nocb_follower_head); -+ -+ /* Having no rcuo kthread but CBs after scheduler starts is bad! */ -+ if (!ACCESS_ONCE(rdp->nocb_kthread) && rhp) { -+ /* RCU callback enqueued before CPU first came online??? */ -+ pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n", -+ cpu, rhp->func); -+ WARN_ON_ONCE(1); -+ } -+ -+ return !!rhp; -+} -+ -+/* - * Enqueue the specified string of rcu_head structures onto the specified - * CPU's no-CBs lists. The CPU is specified by rdp, the head of the - * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy -@@ -2642,6 +2669,12 @@ static bool init_nocb_callback_list(struct rcu_data *rdp) - - #else /* #ifdef CONFIG_RCU_NOCB_CPU */ - -+static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu) -+{ -+ WARN_ON_ONCE(1); /* Should be dead code. */ -+ return false; -+} -+ - static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) - { - } --- -1.9.3 - |