get_next_ino has a number of problems:
- It uses and returns a uint, which is susceptible to become overflowed
if a lot of volatile inodes that use get_next_ino are created.
- It's global, with no specificity per-sb or even per-filesystem. This
means it's not that difficult to cause inode number wraparounds on a
single device, which can result in having multiple distinct inodes
with the same inode number.
This patch adds a per-superblock counter that mitigates the second case.
This design also allows us to later have a specific i_ino size
per-device, for example, allowing users to choose whether to use 32- or
64-bit inodes for each tmpfs mount. This is implemented in the next
commit.
Signed-off-by: Chris Down <chris@xxxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Amir Goldstein <amir73il@xxxxxxxxx>
Cc: Jeff Layton <jlayton@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: kernel-team@xxxxxx
---
include/linux/shmem_fs.h | 1 +
mm/shmem.c | 55 ++++++++++++++++++++++++++++++++++------
2 files changed, 48 insertions(+), 8 deletions(-)
diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index de8e4b71e3ba..dec4353cf3b7 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -35,6 +35,7 @@ struct shmem_sb_info {
unsigned char huge; /* Whether to try for hugepages */
kuid_t uid; /* Mount uid for root directory */
kgid_t gid; /* Mount gid for root directory */
+ ino_t last_ino; /* The last used per-sb inode number */
struct mempolicy *mpol; /* default memory policy for mappings */
spinlock_t shrinklist_lock; /* Protects shrinklist */
struct list_head shrinklist; /* List of shinkable inodes */
diff --git a/mm/shmem.c b/mm/shmem.c
index 165fa6332993..8af9fb922a96 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2235,8 +2235,18 @@ static int shmem_mmap(struct file *file, struct vm_area_struct *vma)
return 0;
}
+/*
+ * shmem_get_inode - reserve, allocate, and initialise a new inode
+ *
+ * If usb_sb_ino is true, we use the per-sb inode allocator to avoid wraparound.
+ * Otherwise, we use get_next_ino, which is global.
+ *
+ * If use_sb_ino is true or max_inodes is greater than 0, we may have to grab
+ * the per-sb stat_lock.
+ */
static struct inode *shmem_get_inode(struct super_block *sb, const struct inode *dir,
- umode_t mode, dev_t dev, unsigned long flags)
+ umode_t mode, dev_t dev,
+ unsigned long flags, bool use_sb_ino)
{
struct inode *inode;
struct shmem_inode_info *info;
@@ -2247,7 +2257,30 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
inode = new_inode(sb);
if (inode) {
- inode->i_ino = get_next_ino();
+ if (use_sb_ino) {
+ spin_lock(&sbinfo->stat_lock);
+ inode->i_ino = sbinfo->last_ino++;
+ if (unlikely(inode->i_ino >= UINT_MAX)) {
+ /*
+ * Emulate get_next_ino uint wraparound for
+ * compatibility
+ */
+ pr_warn("%s: inode number overflow on device %d, consider using inode64 mount option\n",
+ __func__, MINOR(sb->s_dev));
+ inode->i_ino = sbinfo->last_ino = 1;
+ }
+ spin_unlock(&sbinfo->stat_lock);
+ } else {
+ /*
+ * __shmem_file_setup, one of our callers, is lock-free:
+ * it doesn't hold stat_lock in shmem_reserve_inode
+ * since max_inodes is always 0, and is called from
+ * potentially unknown contexts. As such, use the global
+ * allocator which doesn't require the per-sb stat_lock.
+ */
+ inode->i_ino = get_next_ino();
+ }
+
inode_init_owner(inode, dir, mode);
inode->i_blocks = 0;
inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
@@ -2881,7 +2914,7 @@ shmem_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
struct inode *inode;
int error = -ENOSPC;
- inode = shmem_get_inode(dir->i_sb, dir, mode, dev, VM_NORESERVE);
+ inode = shmem_get_inode(dir->i_sb, dir, mode, dev, VM_NORESERVE, true);
if (inode) {
error = simple_acl_create(dir, inode);
if (error)
@@ -2910,7 +2943,7 @@ shmem_tmpfile(struct inode *dir, struct dentry *dentry, umode_t mode)
struct inode *inode;
int error = -ENOSPC;
- inode = shmem_get_inode(dir->i_sb, dir, mode, 0, VM_NORESERVE);
+ inode = shmem_get_inode(dir->i_sb, dir, mode, 0, VM_NORESERVE, true);
if (inode) {
error = security_inode_init_security(inode, dir,
NULL,
@@ -3106,7 +3139,7 @@ static int shmem_symlink(struct inode *dir, struct dentry *dentry, const char *s
return -ENAMETOOLONG;
inode = shmem_get_inode(dir->i_sb, dir, S_IFLNK | 0777, 0,
- VM_NORESERVE);
+ VM_NORESERVE, true);
if (!inode)
return -ENOSPC;
@@ -3378,6 +3411,8 @@ enum shmem_param {
Opt_nr_inodes,
Opt_size,
Opt_uid,
+ Opt_inode32,
+ Opt_inode64,
};
static const struct fs_parameter_spec shmem_param_specs[] = {
@@ -3389,6 +3424,8 @@ static const struct fs_parameter_spec shmem_param_specs[] = {
fsparam_string("nr_inodes", Opt_nr_inodes),
fsparam_string("size", Opt_size),
fsparam_u32 ("uid", Opt_uid),
+ fsparam_flag ("inode32", Opt_inode32),
+ fsparam_flag ("inode64", Opt_inode64),
{}
};
@@ -3690,7 +3727,8 @@ static int shmem_fill_super(struct super_block *sb, struct fs_context *fc)
#endif
uuid_gen(&sb->s_uuid);
- inode = shmem_get_inode(sb, NULL, S_IFDIR | sbinfo->mode, 0, VM_NORESERVE);
+ inode = shmem_get_inode(sb, NULL, S_IFDIR | sbinfo->mode, 0,
+ VM_NORESERVE, true);
if (!inode)
goto failed;
inode->i_uid = sbinfo->uid;
@@ -4081,7 +4119,8 @@ EXPORT_SYMBOL_GPL(shmem_truncate_range);
#define shmem_vm_ops generic_file_vm_ops
#define shmem_file_operations ramfs_file_operations
-#define shmem_get_inode(sb, dir, mode, dev, flags) ramfs_get_inode(sb, dir, mode, dev)
+#define shmem_get_inode(sb, dir, mode, dev, flags, use_sb_ino) \
+ ramfs_get_inode(sb, dir, mode, dev)
#define shmem_acct_size(flags, size) 0
#define shmem_unacct_size(flags, size) do {} while (0)
@@ -4105,7 +4144,7 @@ static struct file *__shmem_file_setup(struct vfsmount *mnt, const char *name, l
return ERR_PTR(-ENOMEM);
inode = shmem_get_inode(mnt->mnt_sb, NULL, S_IFREG | S_IRWXUGO, 0,
- flags);
+ flags, false);
if (unlikely(!inode)) {
shmem_unacct_size(flags, size);
return ERR_PTR(-ENOSPC);
--
2.24.1
