aufs: enter/leave flag per task

In freeing aufs iinfo objects, it acquires the internal rw_sem (see
another commit in detail). Since iinfo can be freed anytime, a deadlock
may happen due to the rw_sem. To prevent this problem, this commit
introduces a flag per task.
This is another (very) ugly approach which I don't like.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

fs/aufs/iinfo.c

@@ -160,12 +160,26 @@ void au_iinfo_fin(struct inode *inode)
 {
 	struct au_iinfo *iinfo;
 	struct au_hinode *hi;
+	struct super_block *sb;
 	aufs_bindex_t bindex, bbot;
 	const unsigned char unlinked = !inode->i_nlink;
 
 	AuDebugOn(au_is_bad_inode(inode));
 
-	au_xino_delete_inode(inode, unlinked);
+	sb = inode->i_sb;
+	if (si_pid_test(sb))
+		au_xino_delete_inode(inode, unlinked);
+	else {
+		/*
+		 * it is safe to hide the dependency between sbinfo and
+		 * sb->s_umount.
+		 */
+		lockdep_off();
+		si_noflush_read_lock(sb);
+		au_xino_delete_inode(inode, unlinked);
+		si_read_unlock(sb);
+		lockdep_on();
+	}
 
 	iinfo = au_ii(inode);
 	bindex = iinfo->ii_btop;

fs/aufs/sbinfo.c

@@ -17,6 +17,7 @@ void au_si_free(struct kobject *kobj)
 {
 	int i;
 	struct au_sbinfo *sbinfo;
+	char *locked __maybe_unused; /* debug only */
 
 	sbinfo = container_of(kobj, struct au_sbinfo, si_kobj);
 	for (i = 0; i < AuPlink_NHASH; i++)
@@ -75,6 +76,7 @@ int au_si_alloc(struct super_block *sb)
 	/* leave other members for sysaufs and si_mnt. */
 	sbinfo->si_sb = sb;
 	sb->s_fs_info = sbinfo;
+	si_pid_set(sb);
 	return 0; /* success */
 
 out_br:

fs/aufs/super.h

@@ -156,6 +156,33 @@ AuStubVoid(au_sbilist_del, struct super_block *sb)
 
 /* ---------------------------------------------------------------------- */
 
+/* current->atomic_flags */
+/* this value should never corrupt the ones defined in linux/sched.h */
+#define PFA_AUFS	7
+
+TASK_PFA_TEST(AUFS, test_aufs)	/* task_test_aufs */
+TASK_PFA_SET(AUFS, aufs)	/* task_set_aufs */
+TASK_PFA_CLEAR(AUFS, aufs)	/* task_clear_aufs */
+
+static inline int si_pid_test(struct super_block *sb)
+{
+	return !!task_test_aufs(current);
+}
+
+static inline void si_pid_clr(struct super_block *sb)
+{
+	AuDebugOn(!task_test_aufs(current));
+	task_clear_aufs(current);
+}
+
+static inline void si_pid_set(struct super_block *sb)
+{
+	AuDebugOn(task_test_aufs(current));
+	task_set_aufs(current);
+}
+
+/* ---------------------------------------------------------------------- */
+
 /* lock superblock. mainly for entry point functions */
 #define __si_read_lock(sb)	au_rw_read_lock(&au_sbi(sb)->si_rwsem)
 #define __si_write_lock(sb)	au_rw_write_lock(&au_sbi(sb)->si_rwsem)
@@ -179,23 +206,33 @@ AuStubVoid(au_sbilist_del, struct super_block *sb)
 static inline void si_noflush_read_lock(struct super_block *sb)
 {
 	__si_read_lock(sb);
-	/* re-commit later */
+	si_pid_set(sb);
 }
 
 static inline int si_noflush_read_trylock(struct super_block *sb)
 {
-	return __si_read_trylock(sb);	/* re-commit later */
+	int locked;
+
+	locked = __si_read_trylock(sb);
+	if (locked)
+		si_pid_set(sb);
+	return locked;
 }
 
 static inline void si_noflush_write_lock(struct super_block *sb)
 {
 	__si_write_lock(sb);
-	/* re-commit later */
+	si_pid_set(sb);
 }
 
 static inline int si_noflush_write_trylock(struct super_block *sb)
 {
-	return __si_write_trylock(sb);	/* re-commit later */
+	int locked;
+
+	locked = __si_write_trylock(sb);
+	if (locked)
+		si_pid_set(sb);
+	return locked;
 }
 
 #if 0 /* reserved */
@@ -209,7 +246,7 @@ static inline int si_read_trylock(struct super_block *sb, int flags)
 
 static inline void si_read_unlock(struct super_block *sb)
 {
-	/* re-commit later */
+	si_pid_clr(sb);
 	__si_read_unlock(sb);
 }
 
@@ -224,7 +261,7 @@ static inline int si_write_trylock(struct super_block *sb, int flags)
 
 static inline void si_write_unlock(struct super_block *sb)
 {
-	/* re-commit later */
+	si_pid_clr(sb);
 	__si_write_unlock(sb);
 }