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@linux.dev>

1 files changed, 144 insertions, 0 deletions

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
+}