util-linux/0071-libmount-introduce-reference-counting-for-libmnt_loc.patch

From 2ae4cd64f0bd535973fa3824c42e66c7e80dc09c Mon Sep 17 00:00:00 2001
From: Karel Zak <kzak@redhat.com>
Date: Fri, 19 Jan 2024 12:15:48 +0100
Subject: libmount: introduce reference counting for libmnt_lock

Addresses: https://issues.redhat.com/browse/RHEL-14612
Upstream: http://github.com/util-linux/util-linux/commit/87938635348a788ffd10cdbfb9055eddc2ed7a9f
Signed-off-by: Karel Zak <kzak@redhat.com>
---
 libmount/docs/libmount-sections.txt |  2 ++
 libmount/src/context.c              |  3 +-
 libmount/src/libmount.h.in          |  2 ++
 libmount/src/libmount.sym           |  8 +++++
 libmount/src/lock.c                 | 49 ++++++++++++++++++++++++++---
 5 files changed, 58 insertions(+), 6 deletions(-)

diff --git a/libmount/docs/libmount-sections.txt b/libmount/docs/libmount-sections.txt
index 89b2b1e8b..d9263b8ad 100644
--- a/libmount/docs/libmount-sections.txt
+++ b/libmount/docs/libmount-sections.txt
@@ -297,6 +297,8 @@ libmnt_lock
 mnt_free_lock
 mnt_lock_file
 mnt_new_lock
+mnt_ref_lock
+mnt_unref_lock
 mnt_unlock_file
 mnt_lock_block_signals
 </SECTION>
diff --git a/libmount/src/context.c b/libmount/src/context.c
index c03b0ea64..ca7ea70d0 100644
--- a/libmount/src/context.c
+++ b/libmount/src/context.c
@@ -101,9 +101,8 @@ void mnt_free_context(struct libmnt_context *cxt)
 	mnt_unref_cache(cxt->cache);
 	mnt_unref_fs(cxt->fs);
 	mnt_unref_fs(cxt->fs_template);
-
 	mnt_context_clear_loopdev(cxt);
-	mnt_free_lock(cxt->lock);
+	mnt_unref_lock(cxt->lock);
 	mnt_free_update(cxt->update);
 
 	mnt_context_set_target_ns(cxt, NULL);
diff --git a/libmount/src/libmount.h.in b/libmount/src/libmount.h.in
index 2d4d044e9..a51ac1ea5 100644
--- a/libmount/src/libmount.h.in
+++ b/libmount/src/libmount.h.in
@@ -417,6 +417,8 @@ extern const struct libmnt_optmap *mnt_get_builtin_optmap(int id);
 /* lock.c */
 extern struct libmnt_lock *mnt_new_lock(const char *datafile, pid_t id)
 			__ul_attribute__((warn_unused_result));
+extern void mnt_ref_lock(struct libmnt_lock *ml);
+extern void mnt_unref_lock(struct libmnt_lock *ml);
 extern void mnt_free_lock(struct libmnt_lock *ml);
 
 extern void mnt_unlock_file(struct libmnt_lock *ml);
diff --git a/libmount/src/libmount.sym b/libmount/src/libmount.sym
index 85e89ad02..88bce5c4b 100644
--- a/libmount/src/libmount.sym
+++ b/libmount/src/libmount.sym
@@ -361,3 +361,11 @@ MOUNT_2_37 {
 	mnt_fs_get_vfs_options_all;
 	mnt_table_over_fs;
 } MOUNT_2_35;
+
+/*
+ * Backport from v2.40 to RHEL 
+ */
+MOUNT_2_40 {
+	mnt_ref_lock;
+	mnt_unref_lock;
+} MOUNT_2_37;
diff --git a/libmount/src/lock.c b/libmount/src/lock.c
index fac64b63b..62353e215 100644
--- a/libmount/src/lock.c
+++ b/libmount/src/lock.c
@@ -36,6 +36,7 @@
  * lock handler
  */
 struct libmnt_lock {
+	int	refcount;	/* reference counter */
 	char	*lockfile;	/* path to lock file (e.g. /etc/mtab~) */
 	char	*linkfile;	/* path to link file (e.g. /etc/mtab~.<id>) */
 	int	lockfile_fd;	/* lock file descriptor */
@@ -82,6 +83,7 @@ struct libmnt_lock *mnt_new_lock(const char *datafile, pid_t id)
 	if (!ml)
 		goto err;
 
+	ml->refcount = 1;
 	ml->lockfile_fd = -1;
 	ml->linkfile = ln;
 	ml->lockfile = lo;
@@ -100,18 +102,57 @@ err:
  * mnt_free_lock:
  * @ml: struct libmnt_lock handler
  *
- * Deallocates mnt_lock.
+ * Deallocates libmnt_lock. This function does not care about reference count. Don't
+ * use this function directly -- it's better to use mnt_unref_lock().
+ *
+ * The reference counting is supported since util-linux v2.40.
  */
 void mnt_free_lock(struct libmnt_lock *ml)
 {
 	if (!ml)
 		return;
-	DBG(LOCKS, ul_debugobj(ml, "free%s", ml->locked ? " !!! LOCKED !!!" : ""));
+
+	DBG(LOCKS, ul_debugobj(ml, "free%s [refcount=%d]",
+					ml->locked ? " !!! LOCKED !!!" : "",
+					ml->refcount));
 	free(ml->lockfile);
 	free(ml->linkfile);
 	free(ml);
 }
 
+/**
+ * mnt_ref_lock:
+ * @ml: lock pointer
+ *
+ * Increments reference counter.
+ *
+ * Since: 2.40
+ */
+void mnt_ref_lock(struct libmnt_lock *ml)
+{
+	if (ml) {
+		ml->refcount++;
+		/*DBG(FS, ul_debugobj(fs, "ref=%d", ml->refcount));*/
+	}
+}
+
+/**
+ * mnt_unref_lock:
+ * @ml: lock pointer
+ *
+ * De-increments reference counter, on zero the @ml is automatically
+ * deallocated by mnt_free_lock).
+ */
+void mnt_unref_lock(struct libmnt_lock *ml)
+{
+	if (ml) {
+		ml->refcount--;
+		/*DBG(FS, ul_debugobj(fs, "unref=%d", ml->refcount));*/
+		if (ml->refcount <= 0)
+			mnt_free_lock(ml);
+	}
+}
+
 /**
  * mnt_lock_block_signals:
  * @ml: struct libmnt_lock handler
@@ -620,7 +661,7 @@ static void clean_lock(void)
 	if (!lock)
 		return;
 	mnt_unlock_file(lock);
-	mnt_free_lock(lock);
+	mnt_unref_lock(lock);
 }
 
 static void __attribute__((__noreturn__)) sig_handler(int sig)
@@ -700,7 +741,7 @@ static int test_lock(struct libmnt_test *ts, int argc, char *argv[])
 		increment_data(datafile, verbose, l);
 
 		mnt_unlock_file(lock);
-		mnt_free_lock(lock);
+		mnt_unref_lock(lock);
 		lock = NULL;
 
 		/* The mount command usually finishes after a mtab update. We
-- 
2.43.0