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locking/lockdep: Reduce space occupied by stack traces

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Although commit 669de8bda8 ("kernel/workqueue: Use dynamic lockdep keys
for workqueues") unregisters dynamic lockdep keys when a workqueue is
destroyed, a side effect of that commit is that all stack traces
associated with the lockdep key are leaked when a workqueue is destroyed.
Fix this by storing each unique stack trace once. Other changes in this
patch are:

- Use NULL instead of { .nr_entries = 0 } to represent 'no trace'.
- Store a pointer to a stack trace in struct lock_class and struct
  lock_list instead of storing 'nr_entries' and 'offset'.

This patch avoids that the following program triggers the "BUG:
MAX_STACK_TRACE_ENTRIES too low!" complaint:

	#include <fcntl.h>
	#include <unistd.h>

	int main()
	{
		for (;;) {
			int fd = open("/dev/infiniband/rdma_cm", O_RDWR);
			close(fd);
		}
	}

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Reported-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Yuyang Du <duyuyang@gmail.com>
Link: https://lkml.kernel.org/r/20190722182443.216015-4-bvanassche@acm.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Bart Van Assche 2019-07-22 11:24:42 -07:00 committed by Ingo Molnar
parent a297042164
commit 12593b7467
3 changed files with 95 additions and 44 deletions
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9
include/linux/lockdep.h
View File

@ -66,10 +66,7 @@ struct lock_class_key {
extern struct lock_class_key __lockdep_no_validate__;
struct lock_trace {
unsigned int nr_entries;
unsigned int offset;
};
struct lock_trace;
#define LOCKSTAT_POINTS 4
@ -105,7 +102,7 @@ struct lock_class {
* IRQ/softirq usage tracking bits:
*/
unsigned long usage_mask;
struct lock_trace usage_traces[XXX_LOCK_USAGE_STATES];
const struct lock_trace *usage_traces[XXX_LOCK_USAGE_STATES];
/*
* Generation counter, when doing certain classes of graph walking,
@ -193,7 +190,7 @@ struct lock_list {
struct list_head entry;
struct lock_class *class;
struct lock_class *links_to;
struct lock_trace trace;
const struct lock_trace *trace;
int distance;
/*

128
kernel/locking/lockdep.c
View File

@ -449,33 +449,72 @@ static void print_lockdep_off(const char *bug_msg)
unsigned long nr_stack_trace_entries;
#ifdef CONFIG_PROVE_LOCKING
/**
* struct lock_trace - single stack backtrace
* @hash_entry: Entry in a stack_trace_hash[] list.
* @hash: jhash() of @entries.
* @nr_entries: Number of entries in @entries.
* @entries: Actual stack backtrace.
*/
struct lock_trace {
struct hlist_node hash_entry;
u32 hash;
u32 nr_entries;
unsigned long entries[0] __aligned(sizeof(unsigned long));
};
#define LOCK_TRACE_SIZE_IN_LONGS \
(sizeof(struct lock_trace) / sizeof(unsigned long))
/*
* Stack-trace: tightly packed array of stack backtrace
* addresses. Protected by the graph_lock.
* Stack-trace: sequence of lock_trace structures. Protected by the graph_lock.
*/
static unsigned long stack_trace[MAX_STACK_TRACE_ENTRIES];
static struct hlist_head stack_trace_hash[STACK_TRACE_HASH_SIZE];
static int save_trace(struct lock_trace *trace)
static bool traces_identical(struct lock_trace *t1, struct lock_trace *t2)
{
unsigned long *entries = stack_trace + nr_stack_trace_entries;
return t1->hash == t2->hash && t1->nr_entries == t2->nr_entries &&
memcmp(t1->entries, t2->entries,
t1->nr_entries * sizeof(t1->entries[0])) == 0;
}
static struct lock_trace *save_trace(void)
{
struct lock_trace *trace, *t2;
struct hlist_head *hash_head;
u32 hash;
unsigned int max_entries;
trace->offset = nr_stack_trace_entries;
max_entries = MAX_STACK_TRACE_ENTRIES - nr_stack_trace_entries;
trace->nr_entries = stack_trace_save(entries, max_entries, 3);
nr_stack_trace_entries += trace->nr_entries;
BUILD_BUG_ON_NOT_POWER_OF_2(STACK_TRACE_HASH_SIZE);
BUILD_BUG_ON(LOCK_TRACE_SIZE_IN_LONGS >= MAX_STACK_TRACE_ENTRIES);
if (nr_stack_trace_entries >= MAX_STACK_TRACE_ENTRIES-1) {
trace = (struct lock_trace *)(stack_trace + nr_stack_trace_entries);
max_entries = MAX_STACK_TRACE_ENTRIES - nr_stack_trace_entries -
LOCK_TRACE_SIZE_IN_LONGS;
trace->nr_entries = stack_trace_save(trace->entries, max_entries, 3);
if (nr_stack_trace_entries >= MAX_STACK_TRACE_ENTRIES -
LOCK_TRACE_SIZE_IN_LONGS - 1) {
if (!debug_locks_off_graph_unlock())
return 0;
return NULL;
print_lockdep_off("BUG: MAX_STACK_TRACE_ENTRIES too low!");
dump_stack();
return 0;
return NULL;
}
return 1;
hash = jhash(trace->entries, trace->nr_entries *
sizeof(trace->entries[0]), 0);
trace->hash = hash;
hash_head = stack_trace_hash + (hash & (STACK_TRACE_HASH_SIZE - 1));
hlist_for_each_entry(t2, hash_head, hash_entry) {
if (traces_identical(trace, t2))
return t2;
}
nr_stack_trace_entries += LOCK_TRACE_SIZE_IN_LONGS + trace->nr_entries;
hlist_add_head(&trace->hash_entry, hash_head);
return trace;
}
#endif
@ -1235,7 +1274,7 @@ static struct lock_list *alloc_list_entry(void)
static int add_lock_to_list(struct lock_class *this,
struct lock_class *links_to, struct list_head *head,
unsigned long ip, int distance,
struct lock_trace *trace)
const struct lock_trace *trace)
{
struct lock_list *entry;
/*
@ -1249,7 +1288,7 @@ static int add_lock_to_list(struct lock_class *this,
entry->class = this;
entry->links_to = links_to;
entry->distance = distance;
entry->trace = *trace;
entry->trace = trace;
/*
* Both allocation and removal are done under the graph lock; but
* iteration is under RCU-sched; see look_up_lock_class() and
@ -1470,11 +1509,10 @@ static inline int __bfs_backwards(struct lock_list *src_entry,
}
static void print_lock_trace(struct lock_trace *trace, unsigned int spaces)
static void print_lock_trace(const struct lock_trace *trace,
unsigned int spaces)
{
unsigned long *entries = stack_trace + trace->offset;
stack_trace_print(entries, trace->nr_entries, spaces);
stack_trace_print(trace->entries, trace->nr_entries, spaces);
}
/*
@ -1489,7 +1527,7 @@ print_circular_bug_entry(struct lock_list *target, int depth)
printk("\n-> #%u", depth);
print_lock_name(target->class);
printk(KERN_CONT ":\n");
print_lock_trace(&target->trace, 6);
print_lock_trace(target->trace, 6);
}
static void
@ -1592,7 +1630,8 @@ static noinline void print_circular_bug(struct lock_list *this,
if (!debug_locks_off_graph_unlock() || debug_locks_silent)
return;
if (!save_trace(&this->trace))
this->trace = save_trace();
if (!this->trace)
return;
depth = get_lock_depth(target);
@ -1715,7 +1754,7 @@ check_path(struct lock_class *target, struct lock_list *src_entry,
*/
static noinline int
check_noncircular(struct held_lock *src, struct held_lock *target,
struct lock_trace *trace)
struct lock_trace **const trace)
{
int ret;
struct lock_list *uninitialized_var(target_entry);
@ -1729,13 +1768,13 @@ check_noncircular(struct held_lock *src, struct held_lock *target,
ret = check_path(hlock_class(target), &src_entry, &target_entry);
if (unlikely(!ret)) {
if (!trace->nr_entries) {
if (!*trace) {
/*
* If save_trace fails here, the printing might
* trigger a WARN but because of the !nr_entries it
* should not do bad things.
*/
save_trace(trace);
*trace = save_trace();
}
print_circular_bug(&src_entry, target_entry, src, target);
@ -1859,7 +1898,7 @@ static void print_lock_class_header(struct lock_class *class, int depth)
len += printk("%*s %s", depth, "", usage_str[bit]);
len += printk(KERN_CONT " at:\n");
print_lock_trace(class->usage_traces + bit, len);
print_lock_trace(class->usage_traces[bit], len);
}
}
printk("%*s }\n", depth, "");
@ -1884,7 +1923,7 @@ print_shortest_lock_dependencies(struct lock_list *leaf,
do {
print_lock_class_header(entry->class, depth);
printk("%*s ... acquired at:\n", depth, "");
print_lock_trace(&entry->trace, 2);
print_lock_trace(entry->trace, 2);
printk("\n");
if (depth == 0 && (entry != root)) {
@ -1995,14 +2034,14 @@ print_bad_irq_dependency(struct task_struct *curr,
print_lock_name(backwards_entry->class);
pr_warn("\n... which became %s-irq-safe at:\n", irqclass);
print_lock_trace(backwards_entry->class->usage_traces + bit1, 1);
print_lock_trace(backwards_entry->class->usage_traces[bit1], 1);
pr_warn("\nto a %s-irq-unsafe lock:\n", irqclass);
print_lock_name(forwards_entry->class);
pr_warn("\n... which became %s-irq-unsafe at:\n", irqclass);
pr_warn("...");
print_lock_trace(forwards_entry->class->usage_traces + bit2, 1);
print_lock_trace(forwards_entry->class->usage_traces[bit2], 1);
pr_warn("\nother info that might help us debug this:\n\n");
print_irq_lock_scenario(backwards_entry, forwards_entry,
@ -2011,13 +2050,15 @@ print_bad_irq_dependency(struct task_struct *curr,
lockdep_print_held_locks(curr);
pr_warn("\nthe dependencies between %s-irq-safe lock and the holding lock:\n", irqclass);
if (!save_trace(&prev_root->trace))
prev_root->trace = save_trace();
if (!prev_root->trace)
return;
print_shortest_lock_dependencies(backwards_entry, prev_root);
pr_warn("\nthe dependencies between the lock to be acquired");
pr_warn(" and %s-irq-unsafe lock:\n", irqclass);
if (!save_trace(&next_root->trace))
next_root->trace = save_trace();
if (!next_root->trace)
return;
print_shortest_lock_dependencies(forwards_entry, next_root);
@ -2369,7 +2410,8 @@ check_deadlock(struct task_struct *curr, struct held_lock *next)
*/
static int
check_prev_add(struct task_struct *curr, struct held_lock *prev,
struct held_lock *next, int distance, struct lock_trace *trace)
struct held_lock *next, int distance,
struct lock_trace **const trace)
{
struct lock_list *entry;
int ret;
@ -2444,8 +2486,11 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
return ret;
#endif
if (!trace->nr_entries && !save_trace(trace))
return 0;
if (!*trace) {
*trace = save_trace();
if (!*trace)
return 0;
}
/*
* Ok, all validations passed, add the new lock
@ -2453,14 +2498,14 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
*/
ret = add_lock_to_list(hlock_class(next), hlock_class(prev),
&hlock_class(prev)->locks_after,
next->acquire_ip, distance, trace);
next->acquire_ip, distance, *trace);
if (!ret)
return 0;
ret = add_lock_to_list(hlock_class(prev), hlock_class(next),
&hlock_class(next)->locks_before,
next->acquire_ip, distance, trace);
next->acquire_ip, distance, *trace);
if (!ret)
return 0;
@ -2476,7 +2521,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
static int
check_prevs_add(struct task_struct *curr, struct held_lock *next)
{
struct lock_trace trace = { .nr_entries = 0 };
struct lock_trace *trace = NULL;
int depth = curr->lockdep_depth;
struct held_lock *hlock;
@ -3015,7 +3060,7 @@ print_usage_bug(struct task_struct *curr, struct held_lock *this,
print_lock(this);
pr_warn("{%s} state was registered at:\n", usage_str[prev_bit]);
print_lock_trace(hlock_class(this)->usage_traces + prev_bit, 1);
print_lock_trace(hlock_class(this)->usage_traces[prev_bit], 1);
print_irqtrace_events(curr);
pr_warn("\nother info that might help us debug this:\n");
@ -3096,7 +3141,8 @@ print_irq_inversion_bug(struct task_struct *curr,
lockdep_print_held_locks(curr);
pr_warn("\nthe shortest dependencies between 2nd lock and 1st lock:\n");
if (!save_trace(&root->trace))
root->trace = save_trace();
if (!root->trace)
return;
print_shortest_lock_dependencies(other, root);
@ -3580,7 +3626,7 @@ static int mark_lock(struct task_struct *curr, struct held_lock *this,
hlock_class(this)->usage_mask |= new_mask;
if (!save_trace(hlock_class(this)->usage_traces + new_bit))
if (!(hlock_class(this)->usage_traces[new_bit] = save_trace()))
return 0;
switch (new_bit) {
@ -5157,6 +5203,12 @@ void __init lockdep_init(void)
) / 1024
);
#if defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING)
printk(" memory used for stack traces: %zu kB\n",
(sizeof(stack_trace) + sizeof(stack_trace_hash)) / 1024
);
#endif
printk(" per task-struct memory footprint: %zu bytes\n",
sizeof(((struct task_struct *)NULL)->held_locks));
}

2
kernel/locking/lockdep_internals.h
View File

@ -92,6 +92,7 @@ static const unsigned long LOCKF_USED_IN_IRQ_READ =
#define MAX_LOCKDEP_ENTRIES 16384UL
#define MAX_LOCKDEP_CHAINS_BITS 15
#define MAX_STACK_TRACE_ENTRIES 262144UL
#define STACK_TRACE_HASH_SIZE 8192
#else
#define MAX_LOCKDEP_ENTRIES 32768UL
@ -102,6 +103,7 @@ static const unsigned long LOCKF_USED_IN_IRQ_READ =
* addresses. Protected by the hash_lock.
*/
#define MAX_STACK_TRACE_ENTRIES 524288UL
#define STACK_TRACE_HASH_SIZE 16384
#endif
#define MAX_LOCKDEP_CHAINS (1UL << MAX_LOCKDEP_CHAINS_BITS)