The patch titled
lockdep: fix combinatorial explosion in lock subgraph traversal
has been added to the -mm tree. Its filename is
lockdep-fix-combinatorial-explosion-in-lock-subgraph-traversal.patch
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------------------------------------------------------
Subject: lockdep: fix combinatorial explosion in lock subgraph traversal
From: David Miller <davem@xxxxxxxxxxxxx>
When we traverse the graph, either forwards or backwards, we are
interested in whether a certain property exists somewhere in a node
reachable in the graph.
Therefore it is never necessary to traverse through a node more than once
to get a correct answer to the given query.
Take advantage of this property using a global ID counter so that we need
not clear all the markers in all the lock_class entries before doing a
traversal. A new ID is choosen when we start to traverse, and we continue
through a lock_class only if it's ID hasn't been marked with the new value
yet.
This short-circuiting is essential especially for high CPU count systems.
The scheduler has a runqueue per cpu, and needs to take two runqueue locks
at a time, which leads to long chains of backwards and forwards subgraphs
from these runqueue lock nodes. Without the short-circuit implemented
here, a graph traversal on a runqueue lock can take up to (1 << (N - 1))
checks on a system with N cpus.
For anything more than 16 cpus or so, lockdep will eventually bring the
machine to a complete standstill.
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/lockdep.h | 1
kernel/lockdep.c | 86 +++++++++++++++++++++++++++++++++++
kernel/lockdep_internals.h | 3 +
kernel/lockdep_proc.c | 34 +------------
4 files changed, 93 insertions(+), 31 deletions(-)
diff -puN include/linux/lockdep.h~lockdep-fix-combinatorial-explosion-in-lock-subgraph-traversal include/linux/lockdep.h
--- a/include/linux/lockdep.h~lockdep-fix-combinatorial-explosion-in-lock-subgraph-traversal
+++ a/include/linux/lockdep.h
@@ -89,6 +89,7 @@ struct lock_class {
struct lockdep_subclass_key *key;
unsigned int subclass;
+ unsigned int dep_gen_id;
/*
* IRQ/softirq usage tracking bits:
diff -puN kernel/lockdep.c~lockdep-fix-combinatorial-explosion-in-lock-subgraph-traversal kernel/lockdep.c
--- a/kernel/lockdep.c~lockdep-fix-combinatorial-explosion-in-lock-subgraph-traversal
+++ a/kernel/lockdep.c
@@ -372,6 +372,19 @@ unsigned int nr_process_chains;
unsigned int max_lockdep_depth;
unsigned int max_recursion_depth;
+static unsigned int lockdep_dependency_gen_id;
+
+static bool lockdep_dependency_visit(struct lock_class *source,
+ unsigned int depth)
+{
+ if (!depth)
+ lockdep_dependency_gen_id++;
+ if (source->dep_gen_id == lockdep_dependency_gen_id)
+ return true;
+ source->dep_gen_id = lockdep_dependency_gen_id;
+ return false;
+}
+
#ifdef CONFIG_DEBUG_LOCKDEP
/*
* We cannot printk in early bootup code. Not even early_printk()
@@ -558,6 +571,9 @@ static void print_lock_dependencies(stru
{
struct lock_list *entry;
+ if (lockdep_dependency_visit(class, depth))
+ return;
+
if (DEBUG_LOCKS_WARN_ON(depth >= 20))
return;
@@ -959,6 +975,67 @@ static int noinline print_infinite_recur
return 0;
}
+unsigned long __lockdep_count_forward_deps(struct lock_class *class,
+ unsigned int depth)
+{
+ struct lock_list *entry;
+ unsigned long ret = 1;
+
+ if (lockdep_dependency_visit(class, depth))
+ return 0;
+
+ /*
+ * Recurse this class's dependency list:
+ */
+ list_for_each_entry(entry, &class->locks_after, entry)
+ ret += __lockdep_count_forward_deps(entry->class, depth + 1);
+
+ return ret;
+}
+
+unsigned long lockdep_count_forward_deps(struct lock_class *class)
+{
+ unsigned long ret, flags;
+
+ local_irq_save(flags);
+ __raw_spin_lock(&lockdep_lock);
+ ret = __lockdep_count_forward_deps(class, 0);
+ __raw_spin_unlock(&lockdep_lock);
+ local_irq_restore(flags);
+
+ return ret;
+}
+
+unsigned long __lockdep_count_backward_deps(struct lock_class *class,
+ unsigned int depth)
+{
+ struct lock_list *entry;
+ unsigned long ret = 1;
+
+ if (lockdep_dependency_visit(class, depth))
+ return 0;
+ /*
+ * Recurse this class's dependency list:
+ */
+ list_for_each_entry(entry, &class->locks_before, entry)
+ ret += __lockdep_count_backward_deps(entry->class, depth + 1);
+
+ return ret;
+}
+
+unsigned long lockdep_count_backward_deps(struct lock_class *class)
+{
+ unsigned long ret, flags;
+
+ local_irq_save(flags);
+ __raw_spin_lock(&lockdep_lock);
+ ret = __lockdep_count_backward_deps(class, 0);
+ __raw_spin_unlock(&lockdep_lock);
+ local_irq_restore(flags);
+
+ return ret;
+}
+
/*
* Prove that the dependency graph starting at <entry> can not
* lead to <target>. Print an error and return 0 if it does.
@@ -968,6 +1045,9 @@ check_noncircular(struct lock_class *sou
{
struct lock_list *entry;
+ if (lockdep_dependency_visit(source, depth))
+ return 1;
+
debug_atomic_inc(&nr_cyclic_check_recursions);
if (depth > max_recursion_depth)
max_recursion_depth = depth;
@@ -1011,6 +1091,9 @@ find_usage_forwards(struct lock_class *s
struct lock_list *entry;
int ret;
+ if (lockdep_dependency_visit(source, depth))
+ return 1;
+
if (depth > max_recursion_depth)
max_recursion_depth = depth;
if (depth >= RECURSION_LIMIT)
@@ -1050,6 +1133,9 @@ find_usage_backwards(struct lock_class *
struct lock_list *entry;
int ret;
+ if (lockdep_dependency_visit(source, depth))
+ return 1;
+
if (!__raw_spin_is_locked(&lockdep_lock))
return DEBUG_LOCKS_WARN_ON(1);
diff -puN kernel/lockdep_internals.h~lockdep-fix-combinatorial-explosion-in-lock-subgraph-traversal kernel/lockdep_internals.h
--- a/kernel/lockdep_internals.h~lockdep-fix-combinatorial-explosion-in-lock-subgraph-traversal
+++ a/kernel/lockdep_internals.h
@@ -53,6 +53,9 @@ extern unsigned int nr_process_chains;
extern unsigned int max_lockdep_depth;
extern unsigned int max_recursion_depth;
+extern unsigned long lockdep_count_forward_deps(struct lock_class *);
+extern unsigned long lockdep_count_backward_deps(struct lock_class *);
+
#ifdef CONFIG_DEBUG_LOCKDEP
/*
* Various lockdep statistics:
diff -puN kernel/lockdep_proc.c~lockdep-fix-combinatorial-explosion-in-lock-subgraph-traversal kernel/lockdep_proc.c
--- a/kernel/lockdep_proc.c~lockdep-fix-combinatorial-explosion-in-lock-subgraph-traversal
+++ a/kernel/lockdep_proc.c
@@ -63,34 +63,6 @@ static void l_stop(struct seq_file *m, v
{
}
-static unsigned long count_forward_deps(struct lock_class *class)
-{
- struct lock_list *entry;
- unsigned long ret = 1;
-
- /*
- * Recurse this class's dependency list:
- */
- list_for_each_entry(entry, &class->locks_after, entry)
- ret += count_forward_deps(entry->class);
-
- return ret;
-}
-
-static unsigned long count_backward_deps(struct lock_class *class)
-{
- struct lock_list *entry;
- unsigned long ret = 1;
-
- /*
- * Recurse this class's dependency list:
- */
- list_for_each_entry(entry, &class->locks_before, entry)
- ret += count_backward_deps(entry->class);
-
- return ret;
-}
-
static void print_name(struct seq_file *m, struct lock_class *class)
{
char str[128];
@@ -124,10 +96,10 @@ static int l_show(struct seq_file *m, vo
#ifdef CONFIG_DEBUG_LOCKDEP
seq_printf(m, " OPS:%8ld", class->ops);
#endif
- nr_forward_deps = count_forward_deps(class);
+ nr_forward_deps = lockdep_count_forward_deps(class);
seq_printf(m, " FD:%5ld", nr_forward_deps);
- nr_backward_deps = count_backward_deps(class);
+ nr_backward_deps = lockdep_count_backward_deps(class);
seq_printf(m, " BD:%5ld", nr_backward_deps);
get_usage_chars(class, &c1, &c2, &c3, &c4);
@@ -350,7 +322,7 @@ static int lockdep_stats_show(struct seq
if (class->usage_mask & LOCKF_ENABLED_HARDIRQS_READ)
nr_hardirq_read_unsafe++;
- sum_forward_deps += count_forward_deps(class);
+ sum_forward_deps += lockdep_count_forward_deps(class);
}
#ifdef CONFIG_DEBUG_LOCKDEP
DEBUG_LOCKS_WARN_ON(debug_atomic_read(&nr_unused_locks) != nr_unused);
_
Patches currently in -mm which might be from davem@xxxxxxxxxxxxx are
origin.patch
radeon-misc-corrections.patch
linux-next.patch
configure-out-igmp-support.patch
lockdep-fix-combinatorial-explosion-in-lock-subgraph-traversal.patch
docsrc-fix-ifenslave-type.patch
ali-m7101-pmu-also-available-on-sun-netras-too.patch
x86-rename-iommu_num_pages-function-to-iommu_nr_pages.patch
sparc64-rename-iommu_num_pages-function-to-iommu_nr_pages.patch
introduce-generic-iommu_num_pages-function.patch
sparc64-use-iommu_num_pages-function-in-iommu-code.patch
kprobes-indirectly-call-kprobe_target.patch
kprobes-add-tests-for-register_kprobes.patch
drivers-net-bonding-bond_sysfsc-suppress-uninitialized-var-warning.patch
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