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Message-ID: <20250420155918.749455-2-kent.overstreet@linux.dev>
Date: Sun, 20 Apr 2025 11:59:14 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: linux-bcachefs@...r.kernel.org,
linux-fsdevel@...r.kernel.org,
linux-hardening@...r.kernel.org,
linux-kernel@...r.kernel.org
Cc: Kent Overstreet <kent.overstreet@...ux.dev>
Subject: [PATCH 1/3] bcachefs: enumerated_ref.c
Factor out the debug code for rw filesystem refs into a small library.
In release mode an enumerated ref is a normal percpu refcount, but in
debug mode all enumerated users of the ref get their own atomic_long_t
ref - making it much easier to chase down refcount usage bugs for when a
refcount has many users.
For debugging, we have enumerated_ref_to_text(), which prints the
current value of each different user.
Additionally, in debug mode enumerated_ref_stop() has a 10 second
timeout, after which it will dump outstanding refcounts.
Signed-off-by: Kent Overstreet <kent.overstreet@...ux.dev>
---
fs/bcachefs/Makefile | 1 +
fs/bcachefs/enumerated_ref.c | 144 +++++++++++++++++++++++++++++
fs/bcachefs/enumerated_ref.h | 54 +++++++++++
fs/bcachefs/enumerated_ref_types.h | 19 ++++
4 files changed, 218 insertions(+)
create mode 100644 fs/bcachefs/enumerated_ref.c
create mode 100644 fs/bcachefs/enumerated_ref.h
create mode 100644 fs/bcachefs/enumerated_ref_types.h
diff --git a/fs/bcachefs/Makefile b/fs/bcachefs/Makefile
index baf859bf83bb..3be39845e4f6 100644
--- a/fs/bcachefs/Makefile
+++ b/fs/bcachefs/Makefile
@@ -35,6 +35,7 @@ bcachefs-y := \
disk_accounting.o \
disk_groups.o \
ec.o \
+ enumerated_ref.o \
errcode.o \
error.o \
extents.o \
diff --git a/fs/bcachefs/enumerated_ref.c b/fs/bcachefs/enumerated_ref.c
new file mode 100644
index 000000000000..56ab430f209f
--- /dev/null
+++ b/fs/bcachefs/enumerated_ref.c
@@ -0,0 +1,144 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "bcachefs.h"
+#include "enumerated_ref.h"
+#include "util.h"
+
+#include <linux/completion.h>
+
+#ifdef ENUMERATED_REF_DEBUG
+void enumerated_ref_get(struct enumerated_ref *ref, unsigned idx)
+{
+ BUG_ON(idx >= ref->nr);
+ atomic_long_inc(&ref->refs[idx]);
+}
+
+bool __enumerated_ref_tryget(struct enumerated_ref *ref, unsigned idx)
+{
+ BUG_ON(idx >= ref->nr);
+ return atomic_long_inc_not_zero(&ref->refs[idx]);
+}
+
+bool enumerated_ref_tryget(struct enumerated_ref *ref, unsigned idx)
+{
+ BUG_ON(idx >= ref->nr);
+ return !ref->dying &&
+ atomic_long_inc_not_zero(&ref->refs[idx]);
+}
+
+void enumerated_ref_put(struct enumerated_ref *ref, unsigned idx)
+{
+ BUG_ON(idx >= ref->nr);
+ long v = atomic_long_dec_return(&ref->refs[idx]);
+
+ BUG_ON(v < 0);
+ if (v)
+ return;
+
+ for (unsigned i = 0; i < ref->nr; i++)
+ if (atomic_long_read(&ref->refs[i]))
+ return;
+
+ if (ref->stop_fn)
+ ref->stop_fn(ref);
+ complete(&ref->stop_complete);
+}
+#endif
+
+#ifndef ENUMERATED_REF_DEBUG
+static void enumerated_ref_kill_cb(struct percpu_ref *percpu_ref)
+{
+ struct enumerated_ref *ref =
+ container_of(percpu_ref, struct enumerated_ref, ref);
+
+ if (ref->stop_fn)
+ ref->stop_fn(ref);
+ complete(&ref->stop_complete);
+}
+#endif
+
+void enumerated_ref_stop_async(struct enumerated_ref *ref)
+{
+ reinit_completion(&ref->stop_complete);
+
+#ifndef ENUMERATED_REF_DEBUG
+ percpu_ref_kill(&ref->ref);
+#else
+ ref->dying = true;
+ for (unsigned i = 0; i < ref->nr; i++)
+ enumerated_ref_put(ref, i);
+#endif
+}
+
+void enumerated_ref_stop(struct enumerated_ref *ref,
+ const char * const names[])
+{
+ enumerated_ref_stop_async(ref);
+ while (!wait_for_completion_timeout(&ref->stop_complete, HZ * 10)) {
+ struct printbuf buf = PRINTBUF;
+
+ prt_str(&buf, "Waited for 10 seconds to shutdown enumerated ref\n");
+ prt_str(&buf, "Outstanding refs:\n");
+ enumerated_ref_to_text(&buf, ref, names);
+ printk(KERN_ERR "%s", buf.buf);
+ printbuf_exit(&buf);
+ }
+}
+
+void enumerated_ref_start(struct enumerated_ref *ref)
+{
+#ifndef ENUMERATED_REF_DEBUG
+ percpu_ref_reinit(&ref->ref);
+#else
+ ref->dying = false;
+ for (unsigned i = 0; i < ref->nr; i++) {
+ BUG_ON(atomic_long_read(&ref->refs[i]));
+ atomic_long_inc(&ref->refs[i]);
+ }
+#endif
+}
+
+void enumerated_ref_exit(struct enumerated_ref *ref)
+{
+#ifndef ENUMERATED_REF_DEBUG
+ percpu_ref_exit(&ref->ref);
+#else
+ kfree(ref->refs);
+ ref->refs = NULL;
+ ref->nr = 0;
+#endif
+}
+
+int enumerated_ref_init(struct enumerated_ref *ref, unsigned nr,
+ void (*stop_fn)(struct enumerated_ref *))
+{
+ init_completion(&ref->stop_complete);
+ ref->stop_fn = stop_fn;
+
+#ifndef ENUMERATED_REF_DEBUG
+ return percpu_ref_init(&ref->ref, enumerated_ref_kill_cb,
+ PERCPU_REF_INIT_DEAD, GFP_KERNEL);
+#else
+ ref->refs = kzalloc(sizeof(ref->refs[0]) * nr, GFP_KERNEL);
+ if (!ref->refs)
+ return -ENOMEM;
+
+ ref->nr = nr;
+ return 0;
+#endif
+}
+
+void enumerated_ref_to_text(struct printbuf *out,
+ struct enumerated_ref *ref,
+ const char * const names[])
+{
+#ifdef ENUMERATED_REF_DEBUG
+ bch2_printbuf_tabstop_push(out, 32);
+
+ for (unsigned i = 0; i < ref->nr; i++)
+ prt_printf(out, "%s\t%li\n", names[i],
+ atomic_long_read(&ref->refs[i]));
+#else
+ prt_str(out, "(not in debug mode)\n");
+#endif
+}
diff --git a/fs/bcachefs/enumerated_ref.h b/fs/bcachefs/enumerated_ref.h
new file mode 100644
index 000000000000..6d2283cf298d
--- /dev/null
+++ b/fs/bcachefs/enumerated_ref.h
@@ -0,0 +1,54 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _BCACHEFS_ENUMERATED_REF_H
+#define _BCACHEFS_ENUMERATED_REF_H
+
+#include "enumerated_ref_types.h"
+
+/*
+ * A refcount where the users are enumerated: in debug mode, we create sepate
+ * refcounts for each user, to make leaks and refcount errors easy to track
+ * down:
+ */
+
+#ifdef ENUMERATED_REF_DEBUG
+void enumerated_ref_get(struct enumerated_ref *, unsigned);
+bool __enumerated_ref_tryget(struct enumerated_ref *, unsigned);
+bool enumerated_ref_tryget(struct enumerated_ref *, unsigned);
+void enumerated_ref_put(struct enumerated_ref *, unsigned);
+#else
+
+static inline void enumerated_ref_get(struct enumerated_ref *ref, unsigned idx)
+{
+ percpu_ref_get(&ref->ref);
+}
+
+static inline bool __enumerated_ref_tryget(struct enumerated_ref *ref, unsigned idx)
+{
+ return percpu_ref_tryget(&ref->ref);
+}
+
+static inline bool enumerated_ref_tryget(struct enumerated_ref *ref, unsigned idx)
+{
+ return percpu_ref_tryget_live(&ref->ref);
+}
+
+static inline void enumerated_ref_put(struct enumerated_ref *ref, unsigned idx)
+{
+ percpu_ref_put(&ref->ref);
+}
+#endif
+
+void enumerated_ref_stop_async(struct enumerated_ref *);
+void enumerated_ref_stop(struct enumerated_ref *, const char * const[]);
+void enumerated_ref_start(struct enumerated_ref *);
+
+void enumerated_ref_exit(struct enumerated_ref *);
+int enumerated_ref_init(struct enumerated_ref *, unsigned,
+ void (*stop_fn)(struct enumerated_ref *));
+
+struct printbuf;
+void enumerated_ref_to_text(struct printbuf *,
+ struct enumerated_ref *,
+ const char * const[]);
+
+#endif /* _BCACHEFS_ENUMERATED_REF_H */
diff --git a/fs/bcachefs/enumerated_ref_types.h b/fs/bcachefs/enumerated_ref_types.h
new file mode 100644
index 000000000000..0e6076f466d3
--- /dev/null
+++ b/fs/bcachefs/enumerated_ref_types.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _BCACHEFS_ENUMERATED_REF_TYPES_H
+#define _BCACHEFS_ENUMERATED_REF_TYPES_H
+
+#include <linux/percpu-refcount.h>
+
+struct enumerated_ref {
+#ifdef ENUMERATED_REF_DEBUG
+ unsigned nr;
+ bool dying;
+ atomic_long_t *refs;
+#else
+ struct percpu_ref ref;
+#endif
+ void (*stop_fn)(struct enumerated_ref *);
+ struct completion stop_complete;
+};
+
+#endif /* _BCACHEFS_ENUMERATED_REF_TYPES_H */
--
2.49.0
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