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Message-Id: <20211117192031.3906502-2-eric.dumazet@gmail.com>
Date: Wed, 17 Nov 2021 11:20:30 -0800
From: Eric Dumazet <eric.dumazet@...il.com>
To: "David S . Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>
Cc: netdev <netdev@...r.kernel.org>,
Eric Dumazet <edumazet@...gle.com>,
Eric Dumazet <eric.dumazet@...il.com>
Subject: [RFC -next 1/2] lib: add reference counting infrastructure
From: Eric Dumazet <edumazet@...gle.com>
It can be hard to track where references are taken and released.
In networking, we have annoying issues at device dismantles,
and we had various proposals to ease root causing them.
This patch adds new infrastructure pairing refcount increases
and decreases. This will self document code, because programmer
will have to associate increments/decrements.
This is controled by CONFIG_REF_TRACKER which can be selected
by users of this feature.
This adds both cpu and memory costs, and thus should be reserved
for debug kernel builds, or be enabled on demand with a static key.
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
include/linux/ref_tracker.h | 78 ++++++++++++++++++++++++
lib/Kconfig | 4 ++
lib/Makefile | 2 +
lib/ref_tracker.c | 116 ++++++++++++++++++++++++++++++++++++
4 files changed, 200 insertions(+)
create mode 100644 include/linux/ref_tracker.h
create mode 100644 lib/ref_tracker.c
diff --git a/include/linux/ref_tracker.h b/include/linux/ref_tracker.h
new file mode 100644
index 0000000000000000000000000000000000000000..1a2a3696682d40b38f9f1dd2b14663716e37d9d3
--- /dev/null
+++ b/include/linux/ref_tracker.h
@@ -0,0 +1,78 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#ifndef _LINUX_REF_TRACKER_H
+#define _LINUX_REF_TRACKER_H
+#include <linux/types.h>
+#include <linux/spinlock.h>
+#include <linux/stackdepot.h>
+
+struct ref_tracker {
+#ifdef CONFIG_REF_TRACKER
+ struct list_head head; /* anchor into dir->list or dir->quarantine */
+ bool dead;
+ depot_stack_handle_t alloc_stack_handle;
+ depot_stack_handle_t free_stack_handle;
+#endif
+};
+
+struct ref_tracker_dir {
+#ifdef CONFIG_REF_TRACKER
+ spinlock_t lock;
+ unsigned int quarantine_avail;
+ struct list_head list; /* List of active trackers */
+ struct list_head quarantine; /* List of dead trackers */
+#endif
+};
+
+#ifdef CONFIG_REF_TRACKER
+static inline void ref_tracker_dir_init(struct ref_tracker_dir *dir,
+ unsigned int quarantine_count)
+{
+ INIT_LIST_HEAD(&dir->list);
+ INIT_LIST_HEAD(&dir->quarantine);
+ spin_lock_init(&dir->lock);
+ dir->quarantine_avail = quarantine_count;
+}
+
+void ref_tracker_dir_exit(struct ref_tracker_dir *dir);
+
+void ref_tracker_dir_print(struct ref_tracker_dir *dir,
+ unsigned int display_limit);
+
+int ref_tracker_alloc(struct ref_tracker_dir *dir,
+ struct ref_tracker **trackerp, gfp_t gfp);
+
+int ref_tracker_free(struct ref_tracker_dir *dir,
+ struct ref_tracker **trackerp);
+
+#else /* CONFIG_REF_TRACKER */
+
+static inline void ref_tracker_dir_init(struct ref_tracker_dir *dir,
+ unsigned int quarantine_count)
+{
+}
+
+static inline void ref_tracker_dir_exit(struct ref_tracker_dir *dir)
+{
+}
+
+static inline void ref_tracker_dir_print(struct ref_tracker_dir *dir,
+ unsigned int display_limit)
+{
+}
+
+static inline int ref_tracker_alloc(struct ref_tracker_dir *dir,
+ struct ref_tracker **trackerp,
+ gfp_t gfp)
+{
+ return 0;
+}
+
+static inline int ref_tracker_free(struct ref_tracker_dir *dir,
+ struct ref_tracker **trackerp)
+{
+ return 0;
+}
+
+#endif
+
+#endif /* _LINUX_REF_TRACKER_H */
diff --git a/lib/Kconfig b/lib/Kconfig
index 5e7165e6a346c9bec878b78c8c8c3d175fc98dfd..d01be8e9593992a7d94a46bd1716460bc33c3ae1 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -680,6 +680,10 @@ config STACK_HASH_ORDER
Select the hash size as a power of 2 for the stackdepot hash table.
Choose a lower value to reduce the memory impact.
+config REF_TRACKER
+ bool
+ select STACKDEPOT
+
config SBITMAP
bool
diff --git a/lib/Makefile b/lib/Makefile
index 364c23f1557816f73aebd8304c01224a4846ac6c..c1fd9243ddb9cc1ac5252d7eb8009f9290782c4a 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -270,6 +270,8 @@ obj-$(CONFIG_STACKDEPOT) += stackdepot.o
KASAN_SANITIZE_stackdepot.o := n
KCOV_INSTRUMENT_stackdepot.o := n
+obj-$(CONFIG_REF_TRACKER) += ref_tracker.o
+
libfdt_files = fdt.o fdt_ro.o fdt_wip.o fdt_rw.o fdt_sw.o fdt_strerror.o \
fdt_empty_tree.o fdt_addresses.o
$(foreach file, $(libfdt_files), \
diff --git a/lib/ref_tracker.c b/lib/ref_tracker.c
new file mode 100644
index 0000000000000000000000000000000000000000..e907c58c31ed49719e31c6e46abd1715d9884924
--- /dev/null
+++ b/lib/ref_tracker.c
@@ -0,0 +1,116 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include <linux/export.h>
+#include <linux/ref_tracker.h>
+#include <linux/slab.h>
+#include <linux/stacktrace.h>
+
+#define REF_TRACKER_STACK_ENTRIES 16
+
+void ref_tracker_dir_exit(struct ref_tracker_dir *dir)
+{
+ struct ref_tracker *tracker, *n;
+ unsigned long flags;
+
+ spin_lock_irqsave(&dir->lock, flags);
+ list_for_each_entry_safe(tracker, n, &dir->quarantine, head) {
+ list_del(&tracker->head);
+ kfree(tracker);
+ dir->quarantine_avail++;
+ }
+ list_for_each_entry_safe(tracker, n, &dir->list, head) {
+ pr_err("leaked reference.\n");
+ if (tracker->alloc_stack_handle)
+ stack_depot_print(tracker->alloc_stack_handle);
+ list_del(&tracker->head);
+ kfree(tracker);
+ }
+ spin_unlock_irqrestore(&dir->lock, flags);
+}
+EXPORT_SYMBOL(ref_tracker_dir_exit);
+
+void ref_tracker_dir_print(struct ref_tracker_dir *dir,
+ unsigned int display_limit)
+{
+ struct ref_tracker *tracker;
+ unsigned long flags;
+ unsigned int i = 0;
+
+ spin_lock_irqsave(&dir->lock, flags);
+ list_for_each_entry(tracker, &dir->list, head) {
+ tracker->dead = true;
+ if (i < display_limit) {
+ pr_err("leaked reference.\n");
+ if (tracker->alloc_stack_handle)
+ stack_depot_print(tracker->alloc_stack_handle);
+ }
+ i++;
+ }
+ spin_unlock_irqrestore(&dir->lock, flags);
+}
+EXPORT_SYMBOL(ref_tracker_dir_print);
+
+int ref_tracker_alloc(struct ref_tracker_dir *dir,
+ struct ref_tracker **trackerp,
+ gfp_t gfp)
+{
+ unsigned long entries[REF_TRACKER_STACK_ENTRIES];
+ struct ref_tracker *tracker;
+ unsigned int nr_entries;
+ unsigned long flags;
+
+ *trackerp = tracker = kzalloc(sizeof(*tracker), gfp);
+ if (!tracker) {
+ pr_err_once("memory allocation failure, unreliable refcount tracker.\n");
+ return -ENOMEM;
+ }
+ nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 1);
+ tracker->alloc_stack_handle = stack_depot_save(entries, nr_entries, gfp);
+
+ spin_lock_irqsave(&dir->lock, flags);
+ list_add(&tracker->head, &dir->list);
+ spin_unlock_irqrestore(&dir->lock, flags);
+ return 0;
+}
+EXPORT_SYMBOL_GPL(ref_tracker_alloc);
+
+int ref_tracker_free(struct ref_tracker_dir *dir,
+ struct ref_tracker **trackerp)
+{
+ unsigned long entries[REF_TRACKER_STACK_ENTRIES];
+ struct ref_tracker *tracker = *trackerp;
+ unsigned int nr_entries;
+ unsigned long flags;
+
+ if (!tracker)
+ return -EEXIST;
+ spin_lock_irqsave(&dir->lock, flags);
+ if (tracker->dead) {
+ pr_err("reference already released.\n");
+ if (tracker->alloc_stack_handle) {
+ pr_err("allocated in:\n");
+ stack_depot_print(tracker->alloc_stack_handle);
+ }
+ if (tracker->free_stack_handle) {
+ pr_err("freed in:\n");
+ stack_depot_print(tracker->free_stack_handle);
+ }
+ spin_unlock_irqrestore(&dir->lock, flags);
+ return -EINVAL;
+ }
+ tracker->dead = true;
+
+ nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 1);
+ tracker->free_stack_handle = stack_depot_save(entries, nr_entries, GFP_ATOMIC);
+
+ list_move_tail(&tracker->head, &dir->quarantine);
+ if (!dir->quarantine_avail) {
+ tracker = list_first_entry(&dir->quarantine, struct ref_tracker, head);
+ list_del(&tracker->head);
+ kfree(tracker);
+ } else {
+ dir->quarantine_avail--;
+ }
+ spin_unlock_irqrestore(&dir->lock, flags);
+ return 0;
+}
+EXPORT_SYMBOL_GPL(ref_tracker_free);
--
2.34.0.rc1.387.gb447b232ab-goog
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