[PATCH] erofs-utils: lib/diskbuf: replace bool locked with a real mutex for MT

[Utkal Singh]

erofs_diskbufstrm used a plain boolean 'locked' to track stream
reservation state, with an explicit comment marking it as a
placeholder: 'need a real lock for MT'.  A boolean provides no
atomicity or memory-ordering guarantees under concurrent access.

Replace 'bool locked' with 'erofs_mutex_t lock' using the existing
portable wrapper in include/erofs/lock.h.  Acquire the mutex in
erofs_diskbuf_reserve() and release it in erofs_diskbuf_commit(),
serialising concurrent access to each stream's tailoffset field.
Initialisation and destruction are wired into erofs_diskbuf_init()
and erofs_diskbuf_exit() respectively.

Also add erofs_mutex_destroy() to include/erofs/lock.h, which was
missing despite erofs_mutex_init() being present.

Signed-off-by: Utkal Singh <singhutkal015 at gmail.com>
---
 include/erofs/lock.h |  2 ++
 lib/diskbuf.c        | 10 ++++++----
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/include/erofs/lock.h b/include/erofs/lock.h
index c6e3093..ef4210d 100644
--- a/include/erofs/lock.h
+++ b/include/erofs/lock.h
@@ -15,6 +15,7 @@ static inline void erofs_mutex_init(erofs_mutex_t *lock)
 }
 #define erofs_mutex_lock	pthread_mutex_lock
 #define erofs_mutex_unlock	pthread_mutex_unlock
+#define erofs_mutex_destroy	pthread_mutex_destroy
 
 #define EROFS_DEFINE_MUTEX(lock)	\
 	erofs_mutex_t lock = PTHREAD_MUTEX_INITIALIZER
@@ -35,6 +36,7 @@ typedef struct {} erofs_mutex_t;
 static inline void erofs_mutex_init(erofs_mutex_t *lock) {}
 static inline void erofs_mutex_lock(erofs_mutex_t *lock) {}
 static inline void erofs_mutex_unlock(erofs_mutex_t *lock) {}
+static inline void erofs_mutex_destroy(erofs_mutex_t *lock) {}
 
 #define EROFS_DEFINE_MUTEX(lock)	\
 	erofs_mutex_t lock = {}
diff --git a/lib/diskbuf.c b/lib/diskbuf.c
index 0bf42da..7f4e6e1 100644
--- a/lib/diskbuf.c
+++ b/lib/diskbuf.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0+ OR Apache-2.0
 #include "erofs/diskbuf.h"
 #include "erofs/internal.h"
+#include "erofs/lock.h"
 #include "erofs/print.h"
 #include <stdio.h>
 #include <errno.h>
@@ -14,7 +15,7 @@ static struct erofs_diskbufstrm {
 	u64 tailoffset, devpos;
 	int fd;
 	unsigned int alignsize;
-	bool locked;
+	erofs_mutex_t lock;
 } *dbufstrm;
 
 int erofs_diskbuf_getfd(struct erofs_diskbuf *db, u64 *fpos)
@@ -42,7 +43,7 @@ int erofs_diskbuf_reserve(struct erofs_diskbuf *db, int sid, u64 *off)
 		*off = db->offset + strm->devpos;
 	db->sp = strm;
 	(void)erofs_atomic_inc_return(&strm->count);
-	strm->locked = true;	/* TODO: need a real lock for MT */
+	erofs_mutex_lock(&strm->lock);
 	return strm->fd;
 }
 
@@ -51,9 +52,9 @@ void erofs_diskbuf_commit(struct erofs_diskbuf *db, u64 len)
 	struct erofs_diskbufstrm *strm = db->sp;
 
 	DBG_BUGON(!strm);
-	DBG_BUGON(!strm->locked);
 	DBG_BUGON(strm->tailoffset != db->offset);
 	strm->tailoffset += len;
+	erofs_mutex_unlock(&strm->lock);
 }
 
 void erofs_diskbuf_close(struct erofs_diskbuf *db)
@@ -115,6 +116,7 @@ int erofs_diskbuf_init(unsigned int nstrms)
 setupone:
 		strm->tailoffset = 0;
 		erofs_atomic_set(&strm->count, 1);
+		erofs_mutex_init(&strm->lock);
 		if (fstat(strm->fd, &st))
 			return -errno;
 		strm->alignsize = max_t(u32, st.st_blksize, getpagesize());
@@ -131,7 +133,7 @@ void erofs_diskbuf_exit(void)
 
 	for (strm = dbufstrm; strm->fd >= 0; ++strm) {
 		DBG_BUGON(erofs_atomic_read(&strm->count) != 1);
-
+		erofs_mutex_destroy(&strm->lock);
 		close(strm->fd);
 		strm->fd = -1;
 	}
-- 
2.43.0