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SubjectRe: [PATCH 01/15] kmemleak: Add the base support
On Sat, 29 Nov 2008 10:43:12 +0000
Catalin Marinas <catalin.marinas@arm.com> wrote:
> This patch adds the base support for the kernel memory leak
> detector. It traces the memory allocation/freeing in a way similar to
> the Boehm's conservative garbage collector, the difference being that
> the unreferenced objects are not freed but only shown in
> /sys/kernel/debug/memleak. Enabling this feature introduces an
> overhead to memory allocations.
>

Please feed all the diffs through checkpatch. You might decide to
ignore some of the warnings, but that script does detect things which
you did not intend to add.

> ---
> include/linux/memleak.h | 87 ++++
> init/main.c | 4
> mm/memleak.c | 1019 +++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 1109 insertions(+), 1 deletions(-)
> create mode 100644 include/linux/memleak.h
> create mode 100644 mm/memleak.c
>
> diff --git a/include/linux/memleak.h b/include/linux/memleak.h
> new file mode 100644
> index 0000000..2756a05
> --- /dev/null
> +++ b/include/linux/memleak.h
> @@ -0,0 +1,87 @@
> +/*
> + * include/linux/memleak.h
> + *
> + * Copyright (C) 2008 ARM Limited
> + * Written by Catalin Marinas <catalin.marinas@arm.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software
> + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
> + */
> +
> +#ifndef __MEMLEAK_H
> +#define __MEMLEAK_H
> +
> +#ifdef CONFIG_DEBUG_MEMLEAK
> +
> +extern void memleak_init(void);
> +extern void memleak_alloc(const void *ptr, size_t size, int ref_count);
> +extern void memleak_free(const void *ptr);
> +extern void memleak_padding(const void *ptr, unsigned long offset, size_t size);
> +extern void memleak_not_leak(const void *ptr);
> +extern void memleak_ignore(const void *ptr);
> +extern void memleak_scan_area(const void *ptr, unsigned long offset, size_t length);
> +
> +static inline void memleak_alloc_recursive(const void *ptr, size_t size,
> + int ref_count, unsigned long flags)
> +{
> + if (!(flags & SLAB_NOLEAKTRACE))
> + memleak_alloc(ptr, size, ref_count);
> +}
> +
> +static inline void memleak_free_recursive(const void *ptr, unsigned long flags)
> +{
> + if (!(flags & SLAB_NOLEAKTRACE))
> + memleak_free(ptr);
> +}
> +
> +static inline void memleak_erase(void **ptr)
> +{
> + *ptr = NULL;
> +}
> +
> +#else
> +
> +#define DECLARE_MEMLEAK_OFFSET(name, type, member)
> +
> +static inline void memleak_init(void)
> +{
> +}
> +static inline void memleak_alloc(const void *ptr, size_t size, int ref_count)
> +{
> +}
> +static inline void memleak_alloc_recursive(const void *ptr, size_t size,
> + int ref_count, unsigned long flags)
> +{
> +}
> +static inline void memleak_free(const void *ptr)
> +{
> +}
> +static inline void memleak_free_recursive(const void *ptr, unsigned long flags)
> +{
> +}
> +static inline void memleak_not_leak(const void *ptr)
> +{
> +}
> +static inline void memleak_ignore(const void *ptr)
> +{
> +}
> +static inline void memleak_scan_area(const void *ptr, unsigned long offset, size_t length)
> +{
> +}
> +static inline void memleak_erase(void **ptr)
> +{
> +}
> +
> +#endif /* CONFIG_DEBUG_MEMLEAK */
> +
> +#endif /* __MEMLEAK_H */
> diff --git a/init/main.c b/init/main.c
> index 7e117a2..81cbbb7 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -56,6 +56,7 @@
> #include <linux/debug_locks.h>
> #include <linux/debugobjects.h>
> #include <linux/lockdep.h>
> +#include <linux/memleak.h>
> #include <linux/pid_namespace.h>
> #include <linux/device.h>
> #include <linux/kthread.h>
> @@ -653,6 +654,8 @@ asmlinkage void __init start_kernel(void)
> enable_debug_pagealloc();
> cpu_hotplug_init();
> kmem_cache_init();
> + prio_tree_init();
> + memleak_init();
> debug_objects_mem_init();
> idr_init_cache();
> setup_per_cpu_pageset();
> @@ -662,7 +665,6 @@ asmlinkage void __init start_kernel(void)
> calibrate_delay();
> pidmap_init();
> pgtable_cache_init();
> - prio_tree_init();

Yeah.

prio_tree_init() could be done at compile-time, even.

> anon_vma_init();
> #ifdef CONFIG_X86
> if (efi_enabled)
> diff --git a/mm/memleak.c b/mm/memleak.c
> new file mode 100644
> index 0000000..1b09ca2
> --- /dev/null
> +++ b/mm/memleak.c
> @@ -0,0 +1,1019 @@
> +/*
> + * mm/memleak.c
> + *
> + * Copyright (C) 2008 ARM Limited
> + * Written by Catalin Marinas <catalin.marinas@arm.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software
> + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
> + */
> +
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> +#include <linux/list.h>
> +#include <linux/sched.h>
> +#include <linux/jiffies.h>
> +#include <linux/delay.h>
> +#include <linux/module.h>
> +#include <linux/kthread.h>
> +#include <linux/prio_tree.h>
> +#include <linux/gfp.h>
> +#include <linux/kallsyms.h>
> +#include <linux/debugfs.h>
> +#include <linux/seq_file.h>
> +#include <linux/cpumask.h>
> +#include <linux/spinlock.h>
> +#include <linux/mutex.h>
> +#include <linux/rcupdate.h>
> +#include <linux/stacktrace.h>
> +#include <linux/cache.h>
> +#include <linux/percpu.h>
> +#include <linux/hardirq.h>
> +#include <linux/mmzone.h>
> +#include <linux/slab.h>
> +
> +#include <asm/sections.h>
> +#include <asm/processor.h>
> +#include <asm/thread_info.h>
> +#include <asm/atomic.h>
> +
> +#include <linux/memleak.h>
> +
> +/*
> + * Kmemleak configuration and common defines.
> + */
> +#define MAX_TRACE 16 /* stack trace length */
> +#define REPORTS_NR 100 /* maximum number of reported leaks */
> +#define MSECS_MIN_AGE 1000 /* minimum object age for leak reporting */
> +#undef SCAN_TASK_STACKS /* scan the task kernel stacks */
> +#undef REPORT_ORPHAN_FREEING /* notify when freeing orphan objects */
> +
> +#define BYTES_PER_WORD sizeof(void *)

This isn't a good idea.

If we need a kernel-wide macro for this then please propose one.

If someone later adds one, they might call it BYTES_PER_WORD, in which
case we'll get duplication or build breakage.

BYTES_PER_POINTER might be a better name.

> +#define MSECS_SCAN_YIELD 10
> +#define SECS_FIRST_SCAN 60
> +#define SECS_SCAN_PERIOD 600
> +
> +/* scanning area inside a memory block */
> +struct memleak_scan_area {
> + struct hlist_node node;
> + unsigned long offset;
> + size_t length;
> +};
> +
> +/* the main allocation tracking object */
> +struct memleak_object {
> + spinlock_t lock;
> + unsigned long flags;
> + struct list_head object_list;
> + struct list_head gray_list;
> + struct prio_tree_node tree_node;
> + struct rcu_head rcu; /* used for object_list lockless traversal */
> + atomic_t use_count; /* internal usage count */
> + unsigned long pointer;
> + size_t size;
> + int ref_count; /* the minimum encounters of the pointer */
> + int count; /* the ecounters of the pointer */

Was that supposed to read "encounters"?

The reader of the above documentation will be wondering what an
"encounter" is.

`count', `refcount' and `use_count' is getting confusing...

> + struct hlist_head area_list; /* areas to be scanned (or empty for all) */
> + unsigned long trace[MAX_TRACE];
> + unsigned int trace_len;
> + unsigned long jiffies; /* creation timestamp */
> + pid_t pid; /* pid of the current task */

Two tasks in different pid namespaces can have the same pid. What
effect will that have upon kmemleak?

> + char comm[TASK_COMM_LEN]; /* executable name */
> +};
> +
> +/* The list of all allocated objects */
> +static LIST_HEAD(object_list);
> +static DEFINE_SPINLOCK(object_list_lock);
> +/* The list of the gray objects */
> +static LIST_HEAD(gray_list);

It would be nice to briefly define the term "gray" before using it.

> +/* prio search tree for object boundaries */
> +static struct prio_tree_root object_tree_root;
> +static DEFINE_RWLOCK(object_tree_lock);
> +
> +/* allocation caches */
> +static struct kmem_cache *object_cache;
> +static struct kmem_cache *scan_area_cache;
> +
> +static atomic_t memleak_enabled = ATOMIC_INIT(0);
> +
> +/* minimum and maximum address that may be valid pointers */
> +static unsigned long min_addr = ~0;

<writes a test program>

OK, I think you got lucky here.

"0" is a signed 32-bit integer, having the all-zeroes pattern.

"~0" is a signed 32-bit integer, having the all-ones bit pattern.

When that gets assigned to an unsigned long it gets sign-extended
first, so you indeed ended up with the 64-bit all-ones pattern.

All very tricky! I like to use plain old "-1" for the all-ones pattern
and let the compiler do the work. It always works.

> +static unsigned long max_addr;
> +
> +/* used for yielding the CPU to other tasks during scanning */
> +static unsigned long next_scan_yield;
> +static struct task_struct *scan_thread;
> +static DEFINE_MUTEX(scan_mutex);
> +static int reported_leaks;
> +static int scan_should_stop;
> +
> +static unsigned long jiffies_scan_yield;
> +static unsigned long jiffies_min_age;
> +
> +/*
> + * Early object allocation (before kmemleak is fully initialised).
> + */
> +#define EARLY_LOG_NR 200
> +
> +enum {
> + MEMLEAK_ALLOC,
> + MEMLEAK_FREE,
> + MEMLEAK_NOT_LEAK,
> + MEMLEAK_IGNORE,
> + MEMLEAK_SCAN_AREA,
> +};

It looks to me like the above states are pretty important to
understanding the code. Perhaps they each should be documented?

> +struct early_log {
> + int op_type; /* kmemleak operation type */
> + const void *ptr;
> + size_t size;
> + int ref_count;
> + unsigned long offset;
> + size_t length;
> +};

Undocumented? What's it for, and what do the fields do?

> +static struct early_log __initdata early_log[EARLY_LOG_NR];

You could in fact remove EARLY_LOG_NR. Just use "200" here, and
ARRAY_SIZE() below. Whatever.

> +static int __initdata crt_early_log;
> +
> +/* object flags */
> +#define OBJECT_ALLOCATED (1 << 0)
> +#define OBJECT_REPORTED (1 << 1)
> +
> +/*
> + * Object colors, encoded with count and ref_count:
> + * - white - orphan object, i.e. not enough references to it (ref_count >= 1)
> + * - gray - referred at least once and therefore non-orphan (ref_count == 0)
> + * - black - ignore; it doesn't contain references (text section) (ref_count == -1).
> + * Newly created objects don't have any color (object->count == -1) before
> + * the next memory scan when they become white.
> + */

ah, there we go.

Please do fit the block comments into 80-columns.

> +static inline int color_white(const struct memleak_object *object)
> +{
> + return object->count != -1 && object->count < object->ref_count;
> +}
> +
> +static inline int color_gray(const struct memleak_object *object)
> +{
> + return object->ref_count != -1 && object->count >= object->ref_count;
> +}
> +
> +static inline int color_black(const struct memleak_object *object)
> +{
> + return object->ref_count == -1;
> +}
> +
> +static inline int unreferenced_object(struct memleak_object *object)
> +{
> + if (color_white(object) &&
> + (object->flags & OBJECT_ALLOCATED) &&
> + time_is_before_eq_jiffies(object->jiffies + jiffies_min_age))
> + return 1;
> + else
> + return 0;
> +}
> +
> +#define print_seq(seq, x...) \
> +do { \
> + if (seq) \
> + seq_printf(seq, x); \
> + else \
> + pr_info(x); \
> +} while (0)
> +
> +static void print_unreferenced(struct seq_file *seq,
> + struct memleak_object *object)
> +{
> + char namebuf[KSYM_NAME_LEN + 1] = "";
> + char *modname;
> + unsigned long symsize;
> + unsigned long offset = 0;

Initialised because gcc is stupid :(

> + int i;
> +
> + print_seq(seq, "unreferenced object 0x%08lx (size %zu):\n",
> + object->pointer, object->size);
> + print_seq(seq, " comm \"%s\", pid %d, jiffies %lu\n",
> + object->comm, object->pid, object->jiffies);
> + print_seq(seq, " backtrace:\n");
> +
> + for (i = 0; i < object->trace_len; i++) {
> + unsigned long trace = object->trace[i];

Could move the definition of `offset' to here.

> + kallsyms_lookup(trace, &symsize, &offset, &modname, namebuf);
> + print_seq(seq, " [<%08lx>] %s\n", trace, namebuf);

We can't use the new %p thing here?

> + }
> +}
> +
> +static void dump_object_info(struct memleak_object *object)
> +{
> + struct stack_trace trace;
> +
> + trace.nr_entries = object->trace_len;
> + trace.entries = object->trace;
> +
> + pr_notice("kmemleak: object 0x%08lx (size %zu):\n",
> + object->tree_node.start, object->size);
> + pr_notice(" comm \"%s\", pid %d, jiffies %lu\n",
> + object->comm, object->pid, object->jiffies);
> + pr_notice(" ref_count = %d\n", object->ref_count);
> + pr_notice(" count = %d\n", object->count);
> + pr_notice(" backtrace:\n");
> + print_stack_trace(&trace, 4);
> +}
> +
> +static struct memleak_object *lookup_object(unsigned long ptr, int alias)
> +{
> + struct prio_tree_node *node;
> + struct prio_tree_iter iter;
> + struct memleak_object *object;
> +
> + prio_tree_iter_init(&iter, &object_tree_root, ptr, ptr);
> + node = prio_tree_next(&iter);
> + if (node) {
> + object = prio_tree_entry(node, struct memleak_object, tree_node);
> + if (!alias && object->pointer != ptr) {
> + pr_warning("kmemleak: found object by alias");
> + object = NULL;
> + }
> + } else
> + object = NULL;
> +
> + return object;
> +}
> +
> +/*
> + * Return 1 if successful or 0 otherwise.
> + */
> +static inline int get_object(struct memleak_object *object)
> +{
> + return atomic_inc_not_zero(&object->use_count);
> +}
> +
> +static void free_object_rcu(struct rcu_head *rcu)
> +{
> + struct hlist_node *elem, *tmp;
> + struct memleak_scan_area *area;
> + struct memleak_object *object =
> + container_of(rcu, struct memleak_object, rcu);
> +
> + /* once use_count is 0, there is no code accessing the object */
> + hlist_for_each_entry_safe(area, elem, tmp, &object->area_list, node) {
> + hlist_del(elem);
> + kmem_cache_free(scan_area_cache, area);
> + }
> + kmem_cache_free(object_cache, object);
> +}
> +
> +static void put_object(struct memleak_object *object)
> +{
> + unsigned long flags;
> +
> + if (!atomic_dec_and_test(&object->use_count))
> + return;
> +
> + /* should only get here after delete_object was called */
> + BUG_ON(object->flags & OBJECT_ALLOCATED);
> +
> + spin_lock_irqsave(&object_list_lock, flags);
> + /* the last reference to this object */
> + list_del_rcu(&object->object_list);
> + call_rcu(&object->rcu, free_object_rcu);
> + spin_unlock_irqrestore(&object_list_lock, flags);
> +}
> +
> +static struct memleak_object *find_and_get_object(unsigned long ptr, int alias)
> +{
> + unsigned long flags;
> + struct memleak_object *object;
> +
> + read_lock_irqsave(&object_tree_lock, flags);
> + object = lookup_object(ptr, alias);
> + if (object)
> + get_object(object);
> + read_unlock_irqrestore(&object_tree_lock, flags);
> +
> + return object;
> +}
> +
> +/*
> + * Insert a pointer into the pointer hash table.
> + */
> +static inline void create_object(unsigned long ptr, size_t size, int ref_count)

I'd suggest removing the `inline', let the compiler work it out.

> +{
> + unsigned long flags;
> + struct memleak_object *object;
> + struct prio_tree_node *node;
> + struct stack_trace trace;
> +
> + object = kmem_cache_alloc(object_cache, GFP_ATOMIC);
> + if (!object)
> + panic("kmemleak: cannot allocate a memleak_object structure\n");

That's a big problem, isn't it? GFP_ATOMIC allocations are quite
unreliable, and we just nuked the machine?

> + INIT_LIST_HEAD(&object->object_list);
> + INIT_LIST_HEAD(&object->gray_list);
> + INIT_HLIST_HEAD(&object->area_list);
> + spin_lock_init(&object->lock);
> + atomic_set(&object->use_count, 1);
> + object->flags = OBJECT_ALLOCATED;
> + object->pointer = ptr;
> + object->size = size;
> + object->ref_count = ref_count;
> + object->count = -1; /* black color initially */
> + object->jiffies = jiffies;
> + if (in_irq()) {
> + object->pid = 0;
> + strncpy(object->comm, "hardirq", TASK_COMM_LEN);
> + } else if (in_softirq()) {
> + object->pid = 0;
> + strncpy(object->comm, "softirq", TASK_COMM_LEN);
> + } else {
> + object->pid = current->pid;
> + strncpy(object->comm, current->comm, TASK_COMM_LEN);

Access to current->comm is a teeny but racy. Use get_task_comm() here.

> + }
> +
> + trace.max_entries = MAX_TRACE;
> + trace.nr_entries = 0;
> + trace.entries = object->trace;
> + trace.skip = 1;
> + save_stack_trace(&trace);
> +
> + object->trace_len = trace.nr_entries;
> +
> + INIT_PRIO_TREE_NODE(&object->tree_node);
> + object->tree_node.start = ptr;
> + object->tree_node.last = ptr + size - 1;
> +
> + if (ptr < min_addr)
> + min_addr = ptr;
> + if (ptr + size > max_addr)
> + max_addr = ptr + size;

Use min() and max()?

> + /*
> + * Update the boundaries before inserting the object in the
> + * prio search tree.
> + */
> + smp_mb();

hm. Is that needed? I hope not, assuming that readers are taking
read_lock(object_tree_lock).

> + write_lock_irqsave(&object_tree_lock, flags);
> + node = prio_tree_insert(&object_tree_root, &object->tree_node);
> + if (node != &object->tree_node) {
> + unsigned long flags;
> +
> + pr_warning("kmemleak: existing pointer\n");
> + dump_stack();
> +
> + object = lookup_object(ptr, 1);
> + spin_lock_irqsave(&object->lock, flags);
> + dump_object_info(object);
> + spin_unlock_irqrestore(&object->lock, flags);
> +
> + panic("kmemleak: cannot insert 0x%lx into the object search tree\n",
> + ptr);
> + }
> + write_unlock_irqrestore(&object_tree_lock, flags);
> +
> + spin_lock_irqsave(&object_list_lock, flags);
> + list_add_tail_rcu(&object->object_list, &object_list);
> + spin_unlock_irqrestore(&object_list_lock, flags);
> +}
> +
> +/*
> + * Remove a pointer from the pointer hash table.
> + */
> +static inline void delete_object(unsigned long ptr)

uninline..

> +{
> + unsigned long flags;
> + struct memleak_object *object;
> +
> + write_lock_irqsave(&object_tree_lock, flags);
> + object = lookup_object(ptr, 0);
> + if (!object) {
> + pr_warning("kmemleak: freeing unknown object at 0x%08lx\n", ptr);
> + dump_stack();
> + write_unlock_irqrestore(&object_tree_lock, flags);
> + return;
> + }
> + prio_tree_remove(&object_tree_root, &object->tree_node);
> + write_unlock_irqrestore(&object_tree_lock, flags);
> +
> + BUG_ON(!(object->flags & OBJECT_ALLOCATED));
> +
> + spin_lock_irqsave(&object->lock, flags);
> + object->flags &= ~OBJECT_ALLOCATED;
> +#ifdef REPORT_ORPHAN_FREEING
> + if (color_white(object)) {
> + pr_warning("kmemleak: freeing orphan object 0x%08lx\n", ptr);
> + dump_stack();
> + dump_object_info(object);
> + }
> +#endif
> + object->pointer = 0;
> + spin_unlock_irqrestore(&object->lock, flags);
> +
> + put_object(object);

Seems strange to take the object's internal lock if we're about to
delete it - nobody else should be using it anyway?

(If that put_object() may not actually free the object then this
observation is wrong..)

> +}
> +
> +/*
> + * Make a object permanently gray (false positive).
> + */
> +static inline void make_gray_object(unsigned long ptr)

Please review all inlining decisions in this patchset.

> +{
> + unsigned long flags;
> + struct memleak_object *object;
> +
> + object = find_and_get_object(ptr, 0);
> + if (!object) {
> + dump_stack();
> + panic("kmemleak: graying unknown object at 0x%08lx\n", ptr);
> + }
> +
> + spin_lock_irqsave(&object->lock, flags);
> + object->ref_count = 0;
> + spin_unlock_irqrestore(&object->lock, flags);
> + put_object(object);
> +}
> +
> +/*
> + * Mark the object as black.
> + */
> +static inline void make_black_object(unsigned long ptr)
> +{
> + unsigned long flags;
> + struct memleak_object *object;
> +
> + object = find_and_get_object(ptr, 0);
> + if (!object) {
> + dump_stack();
> + panic("kmemleak: blacking unknown object at 0x%08lx\n", ptr);
> + }
> +
> + spin_lock_irqsave(&object->lock, flags);
> + object->ref_count = -1;
> + spin_unlock_irqrestore(&object->lock, flags);
> + put_object(object);
> +}
> +
> +/*
> + * Add a scanning area to the object.
> + */
> +static inline void add_scan_area(unsigned long ptr, unsigned long offset, size_t length)

That comment isn't terribly useful ;)

Perhaps it could be enhanced a bit to tell us what a "scanning area"
is, etc.

> +{
> + unsigned long flags;
> + struct memleak_object *object;
> + struct memleak_scan_area *area;
> +
> + object = find_and_get_object(ptr, 0);
> + if (!object) {
> + dump_stack();
> + panic("kmemleak: adding scan area to unknown object at 0x%08lx\n", ptr);
> + }
> +
> + area = kmem_cache_alloc(scan_area_cache, GFP_ATOMIC);
> + if (!area)
> + panic("kmemleak: cannot allocate a scan area\n");

ow, ow, ow.

> + spin_lock_irqsave(&object->lock, flags);
> + if (offset + length > object->size) {
> + dump_stack();
> + dump_object_info(object);
> + panic("kmemleak: scan area larger than object 0x%08lx\n", ptr);
> + }
> +
> + INIT_HLIST_NODE(&area->node);
> + area->offset = offset;
> + area->length = length;
> +
> + hlist_add_head(&area->node, &object->area_list);
> + spin_unlock_irqrestore(&object->lock, flags);
> + put_object(object);
> +}
> +
> +/*
> + * Log the early memleak_* calls.
> + */
> +static void __init memleak_early_log(int op_type, const void *ptr, size_t size,
> + int ref_count,
> + unsigned long offset, size_t length)
> +{
> + unsigned long flags;
> + struct early_log *log;
> +
> + if (crt_early_log >= EARLY_LOG_NR)
> + panic("kmemleak: early log buffer exceeded\n");
> +
> + local_irq_save(flags);
> + log = &early_log[crt_early_log];
> + log->op_type = op_type;
> + log->ptr = ptr;
> + log->size = size;
> + log->ref_count = ref_count;
> + log->offset = offset;
> + log->length = length;
> + crt_early_log++;
> + local_irq_restore(flags);
> +}
> +
> +/*
> + * Allocation function hook.
> + */
> +void memleak_alloc(const void *ptr, size_t size, int ref_count)
> +{
> + pr_debug("%s(0x%p, %zu, %d)\n", __FUNCTION__, ptr, size, ref_count);
> +
> + if (!atomic_read(&memleak_enabled)) {
> + memleak_early_log(MEMLEAK_ALLOC, ptr, size, ref_count, 0, 0);
> + return;
> + }
> + if (!ptr)
> + return;
> +
> + create_object((unsigned long)ptr, size, ref_count);
> +}
> +EXPORT_SYMBOL_GPL(memleak_alloc);

It would be nice to have some description of what all this early log
stuff _is_, and why it exists. I can kinda guess, but I'd prefer not
to have to do so - guessing is unreliable.

> +/*
> + * Freeing function hook.
> + */
> +void memleak_free(const void *ptr)
> +{
> + pr_debug("%s(0x%p)\n", __FUNCTION__, ptr);
> +
> + if (!atomic_read(&memleak_enabled)) {
> + memleak_early_log(MEMLEAK_FREE, ptr, 0, 0, 0, 0);
> + return;
> + }
> + if (!ptr)
> + return;
> +
> + delete_object((unsigned long)ptr);
> +}
> +EXPORT_SYMBOL_GPL(memleak_free);
> +
> +/*
> + * Mark a object as a false positive.
> + */
> +void memleak_not_leak(const void *ptr)
> +{
> + pr_debug("%s(0x%p)\n", __FUNCTION__, ptr);
> +
> + if (!atomic_read(&memleak_enabled)) {
> + memleak_early_log(MEMLEAK_NOT_LEAK, ptr, 0, 0, 0, 0);
> + return;
> + }
> + if (!ptr)
> + return;
> +
> + make_gray_object((unsigned long)ptr);
> +}
> +EXPORT_SYMBOL(memleak_not_leak);

It would be appropriate to have some discussion somewhere describing
what a false positive is, and how it can come about, and how kmemleak
handles them.

Perhaps that's in the documentation somewhere.

> +/*
> + * Ignore this memory object.
> + */
> +void memleak_ignore(const void *ptr)
> +{
> + pr_debug("%s(0x%p)\n", __FUNCTION__, ptr);
> +
> + if (!atomic_read(&memleak_enabled)) {
> + memleak_early_log(MEMLEAK_IGNORE, ptr, 0, 0, 0, 0);
> + return;
> + }
> + if (!ptr)
> + return;
> +
> + make_black_object((unsigned long)ptr);
> +}
> +EXPORT_SYMBOL(memleak_ignore);
> +
> +/*
> + * Add a scanning area to an object.

This comment exactly duplicates the one over add_scan_area(). copy-n-paste?

> + */
> +void memleak_scan_area(const void *ptr, unsigned long offset, size_t length)
> +{
> + pr_debug("%s(0x%p)\n", __FUNCTION__, ptr);
> +
> + if (!atomic_read(&memleak_enabled)) {
> + memleak_early_log(MEMLEAK_SCAN_AREA, ptr, 0, 0, offset, length);
> + return;
> + }
> + if (!ptr)
> + return;
> +
> + add_scan_area((unsigned long)ptr, offset, length);
> +}
> +EXPORT_SYMBOL(memleak_scan_area);
> +
> +static inline void scan_yield(void)
> +{
> + BUG_ON(in_atomic());

Please don't use in_atomic(). It's a low-level internal thing, the
results of which vary according to kernel configuration. checkpatch
does/will/should warn about this.

Using might_sleep() would be appropriate here.

> + if (time_is_before_eq_jiffies(next_scan_yield)) {
> + schedule();
> + next_scan_yield = jiffies + jiffies_scan_yield;
> + }

Why is the yielding rate-limited? The code needs a comment explaining
this, because the reader cannot tell.

> + if (signal_pending(current))
> + scan_should_stop = 1;

That looks odd. per-task signal state will change kernel-wide state?

You can tell that I don't understand how all this code actually works.
It would be nice if I _could_ tell that, from the code and its comments.

<looks around a bit>

Ah, this is run from a kernel thread? Why is kthread_should_stop()
insufficient?

> +}
> +
> +/*
> + * Scan a block of memory (exclusive range) for pointers and move
> + * those found to the gray list.
> + */
> +static void scan_block(void *_start, void *_end, struct memleak_object *scanned)
> +{
> + unsigned long *ptr;
> + unsigned long *start = PTR_ALIGN(_start, BYTES_PER_WORD);
> + unsigned long *end = _end - (BYTES_PER_WORD - 1);
> +
> + for (ptr = start; ptr < end; ptr++) {
> + unsigned long flags;
> + unsigned long pointer = *ptr;
> + struct memleak_object *object;
> +
> + if (scan_should_stop)
> + break;
> +
> + /* If scanned, the CPU is yielded in the calling code */
> + if (!scanned)
> + scan_yield();
> +
> + /*
> + * The boundaries check doesn't need to be precise
> + * (hence no locking) since orphan objects need to
> + * pass a scanning threshold before being reported.
> + */
> + if (pointer < min_addr || pointer >= max_addr)
> + continue;
> +
> + object = find_and_get_object(pointer, 1);
> + if (!object)
> + continue;
> + if (object == scanned) {
> + /* self referenced */
> + put_object(object);
> + continue;
> + }
> +
> + /*
> + * Avoid the lockdep recursive warning on object->lock
> + * being previously acquired in scan_object(). These
> + * locks are enclosed by scan_mutex.
> + */
> + spin_lock_irqsave_nested(&object->lock, flags, SINGLE_DEPTH_NESTING);
> + if (!color_white(object)) {
> + /* non-orphan, ignored or new */
> + spin_unlock_irqrestore(&object->lock, flags);
> + put_object(object);
> + continue;
> + }
> +
> + object->count++;
> + if (color_gray(object))
> + /* the object became gray, add it to the list */
> + list_add_tail(&object->gray_list, &gray_list);
> + else
> + put_object(object);
> + spin_unlock_irqrestore(&object->lock, flags);
> + }
> +}
> +
> +/*
> + * Scan a memory block represented by a memleak_object.
> + */
> +static inline void scan_object(struct memleak_object *object)
> +{
> + struct memleak_scan_area *area;
> + struct hlist_node *elem;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&object->lock, flags);
> +
> + /* freed object */
> + if (!(object->flags & OBJECT_ALLOCATED))
> + goto out;
> +
> + if (hlist_empty(&object->area_list))
> + scan_block((void *)object->pointer,
> + (void *)(object->pointer + object->size), object);
> + else
> + hlist_for_each_entry(area, elem, &object->area_list, node)
> + scan_block((void *)(object->pointer + area->offset),
> + (void *)(object->pointer + area->offset
> + + area->length), object);
> +
> + out:
> + spin_unlock_irqrestore(&object->lock, flags);
> +}
> +
> +/*
> + * Scan the memory and print the orphan objects.
> + */
> +static void memleak_scan(void)
> +{
> + unsigned long flags;
> + struct memleak_object *object, *tmp;
> + int i;
> +#ifdef SCAN_TASK_STACKS
> + struct task_struct *task;
> +#endif
> +
> + scan_should_stop = 0;
> +
> + rcu_read_lock();
> + list_for_each_entry_rcu(object, &object_list, object_list) {
> + spin_lock_irqsave(&object->lock, flags);
> +#ifdef DEBUG
> + /*
> + * With a few exceptions there should be a maximum of
> + * 1 reference to any object at this point.
> + */
> + if (atomic_read(&object->use_count) > 1) {
> + pr_debug("kmemleak: object->use_count = %d\n",
> + atomic_read(&object->use_count));
> + dump_object_info(object);
> + }
> +#endif
> + /* reset the reference count (whiten the object) */
> + object->count = 0;
> + if (color_gray(object) && get_object(object))
> + list_add_tail(&object->gray_list, &gray_list);
> +
> + spin_unlock_irqrestore(&object->lock, flags);
> + }
> + rcu_read_unlock();
> +
> + /* data/bss scanning */
> + scan_block(_sdata, _edata, NULL);
> + scan_block(__bss_start, __bss_stop, NULL);
> +
> +#ifdef CONFIG_SMP
> + /* per-cpu scanning */
> + for_each_possible_cpu(i)
> + scan_block(__per_cpu_start + per_cpu_offset(i),
> + __per_cpu_end + per_cpu_offset(i), NULL);
> +#endif
> +
> + /* mem_map scanning */
> + for_each_online_node(i) {
> + struct page *page, *end;
> +
> + page = NODE_MEM_MAP(i);
> + end = page + NODE_DATA(i)->node_spanned_pages;
> +
> + scan_block(page, end, NULL);
> + }

hmm, do we really need to go this low into the mm data structures?

What assumptions are being made about the contiguity of a node's memory
here?

Perhaps this code should be using pfns and pfn_valid(), dunno.

> +#ifdef SCAN_TASK_STACKS
> + read_lock(&tasklist_lock);
> + for_each_process(task)
> + scan_block(task_stack_page(task),
> + task_stack_page(task) + THREAD_SIZE, NULL);
> + read_unlock(&tasklist_lock);
> +#endif
> +
> + /*
> + * Scan the objects already referenced. More objects will be
> + * referenced and, if there are no memory leaks, all the
> + * objects will be scanned. The list traversal is safe for
> + * both tail additions and removals from inside the loop. The
> + * memleak objects cannot be freed from outside the loop
> + * because their use_count was increased.
> + */
> + object = list_entry(gray_list.next, typeof(*object), gray_list);
> + while (&object->gray_list != &gray_list) {
> + scan_yield();
> +
> + /* may add new objects to the list */
> + if (!scan_should_stop)
> + scan_object(object);
> +
> + tmp = list_entry(object->gray_list.next, typeof(*object),
> + gray_list);
> +
> + /* remove the object from the list and release it */
> + list_del(&object->gray_list);
> + put_object(object);
> +
> + object = tmp;
> + }
> + BUG_ON(!list_empty(&gray_list));
> +}
> +
> +static void *memleak_seq_start(struct seq_file *seq, loff_t *pos)
> +{
> + struct memleak_object *object;
> + loff_t n = *pos;
> +
> + if (!n) {
> + memleak_scan();
> + reported_leaks = 0;
> + }
> + if (reported_leaks >= REPORTS_NR)
> + return NULL;
> +
> + rcu_read_lock();
> + list_for_each_entry_rcu(object, &object_list, object_list) {
> + if (n-- > 0)
> + continue;
> +
> + if (get_object(object))
> + goto out;
> + }
> + object = NULL;
> + out:
> + rcu_read_unlock();
> + return object;
> +}
> +
> +static void *memleak_seq_next(struct seq_file *seq, void *v, loff_t *pos)
> +{
> + struct list_head *n;
> + struct memleak_object *next = NULL;
> + unsigned long flags;
> +
> + ++(*pos);
> + if (reported_leaks >= REPORTS_NR)
> + goto out;
> +
> + spin_lock_irqsave(&object_list_lock, flags);
> + n = ((struct memleak_object *)v)->object_list.next;

Now what's going on here. Can this be cleaned up? container_of(),
list_entry(), etc?

> + if (n != &object_list) {
> + next = list_entry(n, struct memleak_object, object_list);
> + get_object(next);
> + }
> + spin_unlock_irqrestore(&object_list_lock, flags);
> +
> + out:
> + put_object(v);
> + return next;
> +}
> +
> +static void memleak_seq_stop(struct seq_file *seq, void *v)
> +{
> + if (v)

Can `v' be NULL here? Is seq_stop() actually called if seq_start()
returned NULL?

> + put_object(v);
> +}
> +
> +static int memleak_seq_show(struct seq_file *seq, void *v)
> +{
> + struct memleak_object *object = v;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&object->lock, flags);
> + if (!unreferenced_object(object))
> + goto out;
> + print_unreferenced(seq, object);
> + reported_leaks++;

I'm scratching my head over what this does but alas, global variable
reported_leaks is undocumented.

> +out:
> + spin_unlock_irqrestore(&object->lock, flags);
> + return 0;
> +}
> +
> +static struct seq_operations memleak_seq_ops = {

Can be const.

> + .start = memleak_seq_start,
> + .next = memleak_seq_next,
> + .stop = memleak_seq_stop,
> + .show = memleak_seq_show,
> +};
> +
> +static int memleak_seq_open(struct inode *inode, struct file *file)
> +{
> + int ret = mutex_lock_interruptible(&scan_mutex);
> + if (ret < 0)
> + return ret;
> + ret = seq_open(file, &memleak_seq_ops);
> + if (ret < 0)
> + mutex_unlock(&scan_mutex);
> + return ret;
> +}
>
> +static int memleak_seq_release(struct inode *inode, struct file *file)
> +{
> + int ret = seq_release(inode, file);
> + mutex_unlock(&scan_mutex);
> + return ret;
> +}
> +
> +static struct file_operations memleak_fops = {

const

> + .owner = THIS_MODULE,
> + .open = memleak_seq_open,
> + .read = seq_read,
> + .llseek = seq_lseek,
> + .release = memleak_seq_release,
> +};
> +
> +static int memleak_scan_thread(void *arg)
> +{
> + /* sleep before the first scan */

The reader wonders why...

> + ssleep(SECS_FIRST_SCAN);
> +
> + while (!kthread_should_stop()) {
> + struct memleak_object *object;
> +
> + mutex_lock(&scan_mutex);
> +
> + memleak_scan();
> + reported_leaks = 0;
> +
> + rcu_read_lock();
> + list_for_each_entry_rcu(object, &object_list, object_list) {
> + unsigned long flags;
> +
> + if (reported_leaks >= REPORTS_NR)
> + break;
> + spin_lock_irqsave(&object->lock, flags);
> + if (!(object->flags & OBJECT_REPORTED) &&
> + unreferenced_object(object)) {
> + print_unreferenced(NULL, object);
> + object->flags |= OBJECT_REPORTED;
> + reported_leaks++;
> + }
> + spin_unlock_irqrestore(&object->lock, flags);
> + }
> + rcu_read_unlock();
> +
> + mutex_unlock(&scan_mutex);
> + ssleep(SECS_SCAN_PERIOD);
> + }
> +
> + return 0;
> +}
> +
> +/*
> + * Kmemleak initialization.
> + */
> +void __init memleak_init(void)
> +{
> + int i;
> +
> + jiffies_scan_yield = msecs_to_jiffies(MSECS_SCAN_YIELD);
> + jiffies_min_age = msecs_to_jiffies(MSECS_MIN_AGE);
> + object_cache = kmem_cache_create("kmemleak_object",
> + sizeof(struct memleak_object),
> + 0, SLAB_NOLEAKTRACE, NULL);
> + scan_area_cache = kmem_cache_create("kmemleak_scan_area",
> + sizeof(struct memleak_scan_area),
> + 0, SLAB_NOLEAKTRACE, NULL);

We have a little KMEM_CACHE() macro.

> + INIT_PRIO_TREE_ROOT(&object_tree_root);
> +
> + /*
> + * This is the point where tracking allocations is safe.
> + * Scanning is only available later.
> + */
> + atomic_set(&memleak_enabled, 1);
> +
> + /* execute the early logged operations */
> + for (i = 0; i < crt_early_log; i++) {
> + struct early_log *log = &early_log[i];
> +
> + switch (log->op_type) {
> + case MEMLEAK_ALLOC:
> + memleak_alloc(log->ptr, log->size, log->ref_count);
> + break;
> + case MEMLEAK_FREE:
> + memleak_free(log->ptr);
> + break;
> + case MEMLEAK_NOT_LEAK:
> + memleak_not_leak(log->ptr);
> + break;
> + case MEMLEAK_IGNORE:
> + memleak_ignore(log->ptr);
> + break;
> + case MEMLEAK_SCAN_AREA:
> + memleak_scan_area(log->ptr, log->offset, log->length);
> + break;
> + default:
> + BUG();
> + }
> + }
> +}
> +
> +/*
> + * Late initialization function.
> + */
> +static int __init memleak_late_init(void)
> +{
> + struct dentry *dentry;
> +
> + dentry = debugfs_create_file("memleak", S_IRUGO, NULL, NULL,
> + &memleak_fops);
> + if (!dentry)
> + return -ENOMEM;
> +
> + scan_thread = kthread_run(memleak_scan_thread, NULL, "kmemleak");
> + if (IS_ERR(scan_thread))
> + pr_warning("kmemleak: Failed to initialise the scan thread\n");
> +
> + pr_info("Kernel memory leak detector initialized\n");
> +
> + return 0;
> +}
> +late_initcall(memleak_late_init);



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