From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: linux-kernel@vger.kernel.org
Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com,
bobby.prani@gmail.com,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 05/13] rcu: Eliminate panic when silly boot-time fanout specified
Date: Tue, 6 Oct 2015 09:13:40 -0700 [thread overview]
Message-ID: <1444148028-11551-5-git-send-email-paulmck@linux.vnet.ibm.com> (raw)
In-Reply-To: <1444148028-11551-1-git-send-email-paulmck@linux.vnet.ibm.com>
This commit loosens rcutree.rcu_fanout_leaf range checks
and replaces a panic() with a fallback to compile-time values.
This fallback is accompanied by a WARN_ON(), and both occur when the
rcutree.rcu_fanout_leaf value is too small to accommodate the number of
CPUs. For example, given the current four-level limit for the rcu_node
tree, a system with more than 16 CPUs built with CONFIG_FANOUT=2 must
have rcutree.rcu_fanout_leaf larger than 2.
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
Documentation/kernel-parameters.txt | 9 ++++++---
kernel/rcu/tree.c | 20 +++++++++++---------
2 files changed, 17 insertions(+), 12 deletions(-)
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 22a4b687ea5b..23ec96877311 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3074,9 +3074,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
cache-to-cache transfer latencies.
rcutree.rcu_fanout_leaf= [KNL]
- Increase the number of CPUs assigned to each
- leaf rcu_node structure. Useful for very large
- systems.
+ Change the number of CPUs assigned to each
+ leaf rcu_node structure. Useful for very
+ large systems, which will choose the value 64,
+ and for NUMA systems with large remote-access
+ latencies, which will choose a value aligned
+ with the appropriate hardware boundaries.
rcutree.jiffies_till_sched_qs= [KNL]
Set required age in jiffies for a
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 93c0f23c3e45..713eb92314b4 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4230,13 +4230,12 @@ static void __init rcu_init_geometry(void)
rcu_fanout_leaf, nr_cpu_ids);
/*
- * The boot-time rcu_fanout_leaf parameter is only permitted
- * to increase the leaf-level fanout, not decrease it. Of course,
- * the leaf-level fanout cannot exceed the number of bits in
- * the rcu_node masks. Complain and fall back to the compile-
- * time values if these limits are exceeded.
+ * The boot-time rcu_fanout_leaf parameter must be at least two
+ * and cannot exceed the number of bits in the rcu_node masks.
+ * Complain and fall back to the compile-time values if this
+ * limit is exceeded.
*/
- if (rcu_fanout_leaf < RCU_FANOUT_LEAF ||
+ if (rcu_fanout_leaf < 2 ||
rcu_fanout_leaf > sizeof(unsigned long) * 8) {
rcu_fanout_leaf = RCU_FANOUT_LEAF;
WARN_ON(1);
@@ -4253,10 +4252,13 @@ static void __init rcu_init_geometry(void)
/*
* The tree must be able to accommodate the configured number of CPUs.
- * If this limit is exceeded than we have a serious problem elsewhere.
+ * If this limit is exceeded, fall back to the compile-time values.
*/
- if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1])
- panic("rcu_init_geometry: rcu_capacity[] is too small");
+ if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) {
+ rcu_fanout_leaf = RCU_FANOUT_LEAF;
+ WARN_ON(1);
+ return;
+ }
/* Calculate the number of levels in the tree. */
for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
--
2.5.2
next prev parent reply other threads:[~2015-10-06 16:17 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-06 16:13 [PATCH tip/core/rcu 0/13] Miscellaneous fixes for 4.4 Paul E. McKenney
2015-10-06 16:13 ` [PATCH tip/core/rcu 01/13] sched: Export sched_setscheduler_nocheck Paul E. McKenney
2015-10-06 16:13 ` [PATCH tip/core/rcu 02/13] rcu: Use rcu_callback_t in call_rcu*() and friends Paul E. McKenney
2015-10-06 16:13 ` [PATCH tip/core/rcu 03/13] rcu: Use call_rcu_func_t to replace explicit type equivalents Paul E. McKenney
2015-10-06 16:13 ` [PATCH tip/core/rcu 04/13] rcu: Don't disable preemption for Tiny and Tree RCU readers Paul E. McKenney
2015-10-06 16:20 ` [Kernel networking modules.] OSI levels 2 & 3, Assistance - If anyone knows anyone in the US. North West region John D Allen, Leveridge Systems INC
2015-10-06 16:44 ` [PATCH tip/core/rcu 04/13] rcu: Don't disable preemption for Tiny and Tree RCU readers Josh Triplett
2015-10-06 17:01 ` Paul E. McKenney
2015-10-06 17:16 ` Josh Triplett
2015-10-06 17:42 ` Paul E. McKenney
2015-10-06 17:46 ` Josh Triplett
2015-10-06 20:05 ` Peter Zijlstra
2015-10-06 20:18 ` Paul E. McKenney
2015-10-06 20:52 ` Peter Zijlstra
2015-10-06 21:05 ` Paul E. McKenney
2015-10-07 7:19 ` Peter Zijlstra
2015-10-06 16:13 ` Paul E. McKenney [this message]
2015-10-06 16:13 ` [PATCH tip/core/rcu 06/13] rcu: Add online/offline info to stall warning message Paul E. McKenney
2015-10-06 17:15 ` Josh Triplett
2015-10-06 16:13 ` [PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of __srcu_read_lock() Paul E. McKenney
2015-10-06 17:18 ` Josh Triplett
2015-10-06 17:36 ` Paul E. McKenney
2015-10-06 17:43 ` Josh Triplett
2015-10-06 18:07 ` Paul E. McKenney
2015-10-06 20:07 ` Peter Zijlstra
2015-10-06 20:19 ` Paul E. McKenney
2015-10-06 20:32 ` Peter Zijlstra
2015-10-06 21:03 ` Paul E. McKenney
2015-10-07 7:20 ` Peter Zijlstra
2015-10-07 14:18 ` Paul E. McKenney
2015-10-06 16:13 ` [PATCH tip/core/rcu 08/13] rcu: Finish folding ->fqs_state into ->gp_state Paul E. McKenney
2015-10-06 16:13 ` [PATCH tip/core/rcu 09/13] rcu: Correct comment for values of ->gp_state field Paul E. McKenney
2015-10-06 16:13 ` [PATCH tip/core/rcu 10/13] rcu: Add rcu_pointer_handoff() Paul E. McKenney
2015-10-06 17:21 ` Josh Triplett
2015-10-06 17:31 ` Paul E. McKenney
2015-10-06 17:36 ` Josh Triplett
2015-10-06 20:27 ` Peter Zijlstra
2015-10-06 21:02 ` Paul E. McKenney
2015-10-07 7:22 ` Peter Zijlstra
2015-10-07 14:20 ` Paul E. McKenney
2015-10-06 16:13 ` [PATCH tip/core/rcu 11/13] rculist: Make list_entry_rcu() use lockless_dereference() Paul E. McKenney
2015-10-26 8:45 ` Ingo Molnar
2015-10-26 14:55 ` Paul E. McKenney
2015-10-26 18:02 ` Ingo Molnar
2015-10-27 3:37 ` Linus Torvalds
2015-10-27 5:19 ` Tejun Heo
2015-10-27 5:33 ` Paul E. McKenney
2015-10-28 8:33 ` Ingo Molnar
2015-10-28 20:35 ` Patrick Marlier
2015-10-29 0:00 ` Paul E. McKenney
2015-10-29 2:13 ` Tejun Heo
2015-10-28 20:58 ` [tip:core/rcu] fs/writeback, rcu: Don't use list_entry_rcu() for pointer offsetting in bdi_split_work_to_wbs() tip-bot for Tejun Heo
2015-10-27 5:32 ` [PATCH tip/core/rcu 11/13] rculist: Make list_entry_rcu() use lockless_dereference() Paul E. McKenney
2015-10-06 16:13 ` [PATCH tip/core/rcu 12/13] rcu: Remove deprecated rcu_lockdep_assert() Paul E. McKenney
2015-10-06 16:13 ` [PATCH tip/core/rcu 13/13] rculist: Use WRITE_ONCE() when deleting from reader-visible list Paul E. McKenney
2015-10-06 17:23 ` [PATCH tip/core/rcu 0/13] Miscellaneous fixes for 4.4 Josh Triplett
2015-10-06 17:38 ` Paul E. McKenney
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