[PATCH v2 1/8] erofs-utils: use erofs_atomic_t for inode->i_count

[Gao Xiang]

From: Gao Xiang <hsiangkao at linux.alibaba.com>

Since `inode->i_count` can be touched for more than one thread if
multi-threading is enabled.

Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>
---
patchset v1->v2:
 - Fix `--all-fragments` functionality;
 - Fix issues pointed out by Yifan. 

 include/erofs/atomic.h   | 10 ++++++++++
 include/erofs/inode.h    |  2 +-
 include/erofs/internal.h |  3 ++-
 lib/inode.c              |  5 +++--
 4 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/include/erofs/atomic.h b/include/erofs/atomic.h
index 214cdb1..f28687e 100644
--- a/include/erofs/atomic.h
+++ b/include/erofs/atomic.h
@@ -25,4 +25,14 @@ __n;})
 #define erofs_atomic_test_and_set(ptr) \
 	__atomic_test_and_set(ptr, __ATOMIC_RELAXED)
 
+#define erofs_atomic_add_return(ptr, i) \
+	__atomic_add_fetch(ptr, i, __ATOMIC_RELAXED)
+
+#define erofs_atomic_sub_return(ptr, i) \
+	__atomic_sub_fetch(ptr, i, __ATOMIC_RELAXED)
+
+#define erofs_atomic_inc_return(ptr) erofs_atomic_add_return(ptr, 1)
+
+#define erofs_atomic_dec_return(ptr) erofs_atomic_sub_return(ptr, 1)
+
 #endif
diff --git a/include/erofs/inode.h b/include/erofs/inode.h
index d5a732a..5d6bc98 100644
--- a/include/erofs/inode.h
+++ b/include/erofs/inode.h
@@ -17,7 +17,7 @@ extern "C"
 
 static inline struct erofs_inode *erofs_igrab(struct erofs_inode *inode)
 {
-	++inode->i_count;
+	(void)erofs_atomic_inc_return(&inode->i_count);
 	return inode;
 }
 
diff --git a/include/erofs/internal.h b/include/erofs/internal.h
index 4cd2059..f31e548 100644
--- a/include/erofs/internal.h
+++ b/include/erofs/internal.h
@@ -25,6 +25,7 @@ typedef unsigned short umode_t;
 #ifdef HAVE_PTHREAD_H
 #include <pthread.h>
 #endif
+#include "atomic.h"
 
 #ifndef PATH_MAX
 #define PATH_MAX        4096    /* # chars in a path name including nul */
@@ -169,7 +170,7 @@ struct erofs_inode {
 		/* (mkfs.erofs) next pointer for directory dumping */
 		struct erofs_inode *next_dirwrite;
 	};
-	unsigned int i_count;
+	erofs_atomic_t i_count;
 	struct erofs_sb_info *sbi;
 	struct erofs_inode *i_parent;
 
diff --git a/lib/inode.c b/lib/inode.c
index 7508c74..55969d9 100644
--- a/lib/inode.c
+++ b/lib/inode.c
@@ -129,9 +129,10 @@ struct erofs_inode *erofs_iget_by_nid(erofs_nid_t nid)
 unsigned int erofs_iput(struct erofs_inode *inode)
 {
 	struct erofs_dentry *d, *t;
+	unsigned long got = erofs_atomic_dec_return(&inode->i_count);
 
-	if (inode->i_count > 1)
-		return --inode->i_count;
+	if (got >= 1)
+		return got;
 
 	list_for_each_entry_safe(d, t, &inode->i_subdirs, d_child)
 		free(d);
-- 
2.30.2