Re: [PATCH v2] vfs: get_next_ino(), never inum=0

["J. R. Okajima" <hooanon05g@gmail.com>]

Carlos Maiolino:
> This V2 looks very reasonable, and fix the problem with files with inode=0 on
> tmpfs which I tested here, so, consider it
>
> Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>

Just out of curious, how did you notice the problem of inode=0? I think
it is hard for everyone to meet the problem.

And after posting the patch, some people reported me a bug related to
Sysv shm. This extra patch supports Sysv shm. But I don't like it since
it introduces an additional condition into the very normal path.


J. R. Okajima

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index ca658a8..fda816e 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -25,6 +25,7 @@ struct shmem_inode_info {
 
 struct shmem_sb_info {
 	struct mutex idr_lock;
+	bool idr_nouse;
 	struct idr idr;		    /* manages inode-number */
 	unsigned long max_blocks;   /* How many blocks are allowed */
 	struct percpu_counter used_blocks;  /* How many are allocated */
diff --git a/mm/shmem.c b/mm/shmem.c
index 0aa3b85..5eb75e9 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -648,7 +648,7 @@ static void shmem_evict_inode(struct inode *inode)
 
 	simple_xattrs_free(&info->xattrs);
 	WARN_ON(inode->i_blocks);
-	if (inode->i_ino) {
+	if (!sbinfo->idr_nouse && inode->i_ino) {
 		mutex_lock(&sbinfo->idr_lock);
 		idr_remove(&sbinfo->idr, inode->i_ino);
 		mutex_unlock(&sbinfo->idr_lock);
@@ -1423,19 +1423,24 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
 			break;
 		}
 
-		/* inum 0 and 1 are unused */
-		mutex_lock(&sbinfo->idr_lock);
-		ino = idr_alloc(&sbinfo->idr, inode, 2, INT_MAX, GFP_NOFS);
-		if (ino > 0) {
-			inode->i_ino = ino;
-			mutex_unlock(&sbinfo->idr_lock);
-			__insert_inode_hash(inode, inode->i_ino);
-		} else {
-			inode->i_ino = 0;
-			mutex_unlock(&sbinfo->idr_lock);
-			iput(inode);	/* shmem_free_inode() will be called */
-			inode = NULL;
-		}
+		if (!sbinfo->idr_nouse) {
+			/* inum 0 and 1 are unused */
+			mutex_lock(&sbinfo->idr_lock);
+			ino = idr_alloc(&sbinfo->idr, inode, 2, INT_MAX,
+					GFP_NOFS);
+			if (ino > 0) {
+				inode->i_ino = ino;
+				mutex_unlock(&sbinfo->idr_lock);
+				__insert_inode_hash(inode, inode->i_ino);
+			} else {
+				inode->i_ino = 0;
+				mutex_unlock(&sbinfo->idr_lock);
+				iput(inode);
+				/* shmem_free_inode() will be called */
+				inode = NULL;
+			}
+		} else
+			inode->i_ino = get_next_ino();
 	} else
 		shmem_free_inode(sb);
 	return inode;
@@ -2560,7 +2565,8 @@ static void shmem_put_super(struct super_block *sb)
 {
 	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
 
-	idr_destroy(&sbinfo->idr);
+	if (!sbinfo->idr_nouse)
+		idr_destroy(&sbinfo->idr);
 	percpu_counter_destroy(&sbinfo->used_blocks);
 	mpol_put(sbinfo->mpol);
 	kfree(sbinfo);
@@ -2682,6 +2688,15 @@ static void shmem_destroy_inodecache(void)
 	kmem_cache_destroy(shmem_inode_cachep);
 }
 
+static __init void shmem_no_idr(struct super_block *sb)
+{
+	struct shmem_sb_info *sbinfo;
+
+	sbinfo = SHMEM_SB(sb);
+	sbinfo->idr_nouse = true;
+	idr_destroy(&sbinfo->idr);
+}
+
 static const struct address_space_operations shmem_aops = {
 	.writepage	= shmem_writepage,
 	.set_page_dirty	= __set_page_dirty_no_writeback,
@@ -2814,6 +2829,7 @@ int __init shmem_init(void)
 		printk(KERN_ERR "Could not kern_mount tmpfs\n");
 		goto out1;
 	}
+	shmem_no_idr(shm_mnt->mnt_sb);
 	return 0;
 
 out1: