aufs: remount 1/5, an array of the cached inodes

As a part of branch-management, aufs maintains all cached inodes,
dentries, and opened files in remounting.
This commits handles the cached inodes by counting the number of cached
inodes, generating an array of their pointers. I don't like such array
approach, but I don't have another idea.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

fs/aufs/iinfo.c

@@ -191,6 +191,8 @@ int au_iinfo_init(struct inode *inode)
 		nbr = 1;
 	hi = kmalloc_array(nbr, sizeof(*iinfo->ii_hinode), GFP_NOFS);
 	if (hi) {
+		au_lcnt_inc(&au_sbi(sb)->si_ninodes);
+
 		iinfo->ii_hinode = hi;
 		for (i = 0; i < nbr; i++, hi++)
 			au_hinode_init(hi);
@@ -237,6 +239,7 @@ void au_iinfo_fin(struct inode *inode)
 	AuDebugOn(au_is_bad_inode(inode));
 
 	sb = inode->i_sb;
+	au_lcnt_dec(&au_sbi(sb)->si_ninodes);
 	if (si_pid_test(sb))
 		au_xino_delete_inode(inode, unlinked);
 	else {

fs/aufs/sbinfo.c

@@ -24,6 +24,9 @@ void au_si_free(struct kobject *kobj)
 		AuDebugOn(!hlist_bl_empty(sbinfo->si_plink + i));
 	AuDebugOn(atomic_read(&sbinfo->si_nowait.nw_len));
 
+	AuLCntZero(au_lcnt_read(&sbinfo->si_ninodes, /*do_rev*/0));
+	au_lcnt_fin(&sbinfo->si_ninodes, /*do_sync*/0);
+
 	au_rw_write_lock(&sbinfo->si_rwsem);
 	au_br_free(sbinfo);
 	au_rw_write_unlock(&sbinfo->si_rwsem);
@@ -32,6 +35,7 @@ void au_si_free(struct kobject *kobj)
 	mutex_destroy(&sbinfo->si_xib_mtx);
 	AuRwDestroy(&sbinfo->si_rwsem);
 
+	au_lcnt_wait_for_fin(&sbinfo->si_ninodes);
 	au_kfree_rcu(sbinfo);
 }
 
@@ -57,6 +61,8 @@ int au_si_alloc(struct super_block *sb)
 	au_nwt_init(&sbinfo->si_nowait);
 	au_rw_init_wlock(&sbinfo->si_rwsem);
 
+	au_lcnt_init(&sbinfo->si_ninodes, /*release*/NULL);
+
 	sbinfo->si_bbot = -1;
 	sbinfo->si_last_br_id = AUFS_BRANCH_MAX / 2;
 

fs/aufs/super.c

@@ -8,7 +8,9 @@
  */
 
 #include <linux/iversion.h>
+#include <linux/mm.h>
 #include <linux/seq_file.h>
+#include <linux/vmalloc.h>
 #include "aufs.h"
 
 /*
@@ -222,6 +224,90 @@ static void aufs_put_super(struct super_block *sb)
 
 /* ---------------------------------------------------------------------- */
 
+void *au_array_alloc(unsigned long long *hint, au_arraycb_t cb,
+		     struct super_block *sb, void *arg)
+{
+	void *array;
+	unsigned long long n, sz;
+
+	array = NULL;
+	n = 0;
+	if (!*hint)
+		goto out;
+
+	if (*hint > ULLONG_MAX / sizeof(array)) {
+		array = ERR_PTR(-EMFILE);
+		pr_err("hint %llu\n", *hint);
+		goto out;
+	}
+
+	sz = sizeof(array) * *hint;
+	array = kzalloc(sz, GFP_NOFS);
+	if (unlikely(!array))
+		array = vzalloc(sz);
+	if (unlikely(!array)) {
+		array = ERR_PTR(-ENOMEM);
+		goto out;
+	}
+
+	n = cb(sb, array, *hint, arg);
+	AuDebugOn(n > *hint);
+
+out:
+	*hint = n;
+	return array;
+}
+
+static unsigned long long au_iarray_cb(struct super_block *sb, void *a,
+				       unsigned long long max __maybe_unused,
+				       void *arg)
+{
+	unsigned long long n;
+	struct inode **p, *inode;
+	struct list_head *head;
+
+	n = 0;
+	p = a;
+	head = arg;
+	spin_lock(&sb->s_inode_list_lock);
+	list_for_each_entry(inode, head, i_sb_list) {
+		if (!au_is_bad_inode(inode)
+		    && au_ii(inode)->ii_btop >= 0) {
+			spin_lock(&inode->i_lock);
+			if (atomic_read(&inode->i_count)) {
+				au_igrab(inode);
+				*p++ = inode;
+				n++;
+				AuDebugOn(n > max);
+			}
+			spin_unlock(&inode->i_lock);
+		}
+	}
+	spin_unlock(&sb->s_inode_list_lock);
+
+	return n;
+}
+
+struct inode **au_iarray_alloc(struct super_block *sb, unsigned long long *max)
+{
+	struct au_sbinfo *sbi;
+
+	sbi = au_sbi(sb);
+	*max = au_lcnt_read(&sbi->si_ninodes, /*do_rev*/1);
+	return au_array_alloc(max, au_iarray_cb, sb, &sb->s_inodes);
+}
+
+void au_iarray_free(struct inode **a, unsigned long long max)
+{
+	unsigned long long ull;
+
+	for (ull = 0; ull < max; ull++)
+		iput(a[ull]);
+	kvfree(a);
+}
+
+/* ---------------------------------------------------------------------- */
+
 /* stop extra interpretation of errno in mount(8), and strange error messages */
 static int cvt_err(int err)
 {

fs/aufs/super.h

@@ -15,6 +15,7 @@
 #include <linux/fs.h>
 #include <linux/kobject.h>
 #include "hbl.h"
+#include "lcnt.h"
 #include "rwsem.h"
 #include "wkq.h"
 
@@ -63,6 +64,12 @@ struct au_sbinfo {
 	 */
 	struct au_rwsem		si_rwsem;
 
+	/*
+	 * dirty approach to protect sb->sb_inodes from
+	 * remount.
+	 */
+	au_lcnt_t		si_ninodes;
+
 	/* branch management */
 	unsigned int		si_generation;
 
@@ -166,6 +173,12 @@ struct au_sbinfo {
 /* super.c */
 extern struct file_system_type aufs_fs_type;
 struct inode *au_iget_locked(struct super_block *sb, ino_t ino);
+typedef unsigned long long (*au_arraycb_t)(struct super_block *sb, void *array,
+					   unsigned long long max, void *arg);
+void *au_array_alloc(unsigned long long *hint, au_arraycb_t cb,
+		     struct super_block *sb, void *arg);
+struct inode **au_iarray_alloc(struct super_block *sb, unsigned long long *max);
+void au_iarray_free(struct inode **a, unsigned long long max);
 
 /* sbinfo.c */
 void au_si_free(struct kobject *kobj);