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Date: Wed, 8 Dec 2021 15:27:10 +0100
From: Dmitry Vyukov <dvyukov@...gle.com>
To: Andrzej Hajda <andrzej.hajda@...el.com>
Cc: Eric Dumazet <eric.dumazet@...il.com>,
"David S . Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
netdev <netdev@...r.kernel.org>,
Eric Dumazet <edumazet@...gle.com>,
Thomas Gleixner <tglx@...utronix.de>, Greg KH <greg@...ah.com>,
Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v3 net-next 01/23] lib: add reference counting tracking infrastructure
On Wed, 8 Dec 2021 at 15:09, Andrzej Hajda <andrzej.hajda@...el.com> wrote:
>
> Hi Eric,
>
>
> I've spotted this patchset thanks to LWN, anyway it was merged very
> quickly, I think it missed more broader review.
>
> As the patch touches kernel lib I have added few people who could be
> interested.
>
>
> On 05.12.2021 05:21, Eric Dumazet wrote:
> > 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 or netns 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 programmers
> > 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 probably be
> > used with care.
> >
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > Reviewed-by: Dmitry Vyukov <dvyukov@...gle.com>
> > ---
>
>
> Life is surprising, I was working on my own framework, solving the same
> issue, with intention to publish it in few days :)
>
>
> My approach was little different:
>
> 1. Instead of creating separate framework I have extended debug_objects.
>
> 2. There were no additional fields in refcounted object and trackers -
> infrastructure of debug_objects was reused - debug_objects tracked both
> pointers of refcounted object and its users.
>
> Have you considered using debug_object? it seems to be good place to put
> it there, I am not sure about performance differences.
Hi Andrzej,
How exactly did you do it? Do you have a link to your patch?
There still should be something similar to `struct ref_tracker` in
this patch, right? Or how do you match decrements with increments and
understand when a double-decrement happens?
> One more thing about design - as I understand CONFIG_REF_TRACKER turns
> on all trackers in whole kernel, have you considered possibility/helpers
> to enable/disable tracking per class of objects?
>
>
> > include/linux/ref_tracker.h | 73 +++++++++++++++++++
> > lib/Kconfig | 5 ++
> > lib/Makefile | 2 +
> > lib/ref_tracker.c | 140 ++++++++++++++++++++++++++++++++++++
> > 4 files changed, 220 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..c11c9db5825cf933acf529c83db441a818135f29
> > --- /dev/null
> > +++ b/include/linux/ref_tracker.h
> > @@ -0,0 +1,73 @@
> > +// SPDX-License-Identifier: GPL-2.0-or-later
> > +#ifndef _LINUX_REF_TRACKER_H
> > +#define _LINUX_REF_TRACKER_H
> > +#include <linux/refcount.h>
> > +#include <linux/types.h>
> > +#include <linux/spinlock.h>
> > +
> > +struct ref_tracker;
>
>
> With sth similar to:
>
> #ifdef CONFIG_REF_TRACKER
>
> typedef struct ref_tracker *ref_tracker_p;
> #else
> typedef struct {} ref_tracker_p;
> #endif
>
> you can eliminate unused field in user's structures.
>
> Beside this it looks OK to me.
>
>
> Regards
>
> Andrzej
>
>
> > +
> > +struct ref_tracker_dir {
> > +#ifdef CONFIG_REF_TRACKER
> > + spinlock_t lock;
> > + unsigned int quarantine_avail;
> > + refcount_t untracked;
> > + 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;
> > + refcount_set(&dir->untracked, 1);
> > +}
> > +
> > +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..655b0e43f260bfca63240794191e3f1890b2e801 100644
> > --- a/lib/Kconfig
> > +++ b/lib/Kconfig
> > @@ -680,6 +680,11 @@ 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
> > + depends on STACKTRACE_SUPPORT
> > + 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..0ae2e66dcf0fdb976f4cb99e747c9448b37f22cc
> > --- /dev/null
> > +++ b/lib/ref_tracker.c
> > @@ -0,0 +1,140 @@
> > +// 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>
> > +#include <linux/stackdepot.h>
> > +
> > +#define REF_TRACKER_STACK_ENTRIES 16
> > +
> > +struct 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;
> > +};
> > +
> > +void ref_tracker_dir_exit(struct ref_tracker_dir *dir)
> > +{
> > + struct ref_tracker *tracker, *n;
> > + unsigned long flags;
> > + bool leak = false;
> > +
> > + 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);
> > + leak = true;
> > + list_del(&tracker->head);
> > + kfree(tracker);
> > + }
> > + spin_unlock_irqrestore(&dir->lock, flags);
> > + WARN_ON_ONCE(leak);
> > + WARN_ON_ONCE(refcount_read(&dir->untracked) != 1);
> > +}
> > +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) {
> > + if (i < display_limit) {
> > + pr_err("leaked reference.\n");
> > + if (tracker->alloc_stack_handle)
> > + stack_depot_print(tracker->alloc_stack_handle);
> > + i++;
> > + } else {
> > + break;
> > + }
> > + }
> > + 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 | __GFP_NOFAIL);
> > + if (unlikely(!tracker)) {
> > + pr_err_once("memory allocation failure, unreliable refcount tracker.\n");
> > + refcount_inc(&dir->untracked);
> > + return -ENOMEM;
> > + }
> > + nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 1);
> > + nr_entries = filter_irq_stacks(entries, nr_entries);
> > + 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;
> > + depot_stack_handle_t stack_handle;
> > + unsigned int nr_entries;
> > + unsigned long flags;
> > +
> > + if (!tracker) {
> > + refcount_dec(&dir->untracked);
> > + return -EEXIST;
> > + }
> > + nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 1);
> > + nr_entries = filter_irq_stacks(entries, nr_entries);
> > + stack_handle = stack_depot_save(entries, nr_entries, GFP_ATOMIC);
> > +
> > + 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);
> > + WARN_ON_ONCE(1);
> > + return -EINVAL;
> > + }
> > + tracker->dead = true;
> > +
> > + tracker->free_stack_handle = stack_handle;
> > +
> > + 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);
> > + } else {
> > + dir->quarantine_avail--;
> > + tracker = NULL;
> > + }
> > + spin_unlock_irqrestore(&dir->lock, flags);
> > +
> > + kfree(tracker);
> > + return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(ref_tracker_free);
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