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mqueue: switch to on-demand creation of internal mount

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Instead of doing that upon each ipcns creation, we do that the first
time mq_open(2) or mqueue mount is done in an ipcns.  What's more,
doing that allows to get rid of mount_ns() use - we can go with
considerably cheaper mount_nodev(), avoiding the loop over all
mqueue superblock instances; ipcns->mq_mnt is used to locate preexisting
instance in O(1) time instead of O(instances) mount_ns() would've
cost us.

Based upon the version by Giuseppe Scrivano <gscrivan@redhat.com>; I've
added handling of userland mqueue mounts (original had been broken in
that area) and added a switch to mount_nodev().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2017-12-25 19:43:35 -05:00
parent a713fd7f52
commit 36735a6a2b
1 changed files with 55 additions and 19 deletions
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74
ipc/mqueue.c
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@ -325,8 +325,9 @@ static struct inode *mqueue_get_inode(struct super_block *sb,
static int mqueue_fill_super(struct super_block *sb, void *data, int silent)
{
struct inode *inode;
struct ipc_namespace *ns = sb->s_fs_info;
struct ipc_namespace *ns = data;
sb->s_fs_info = ns;
sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
sb->s_blocksize = PAGE_SIZE;
sb->s_blocksize_bits = PAGE_SHIFT;
@ -343,18 +344,44 @@ static int mqueue_fill_super(struct super_block *sb, void *data, int silent)
return 0;
}
static struct file_system_type mqueue_fs_type;
/*
* Return value is pinned only by reference in ->mq_mnt; it will
* live until ipcns dies. Caller does not need to drop it.
*/
static struct vfsmount *mq_internal_mount(void)
{
struct ipc_namespace *ns = current->nsproxy->ipc_ns;
struct vfsmount *m = ns->mq_mnt;
if (m)
return m;
m = kern_mount_data(&mqueue_fs_type, ns);
spin_lock(&mq_lock);
if (unlikely(ns->mq_mnt)) {
spin_unlock(&mq_lock);
if (!IS_ERR(m))
kern_unmount(m);
return ns->mq_mnt;
}
if (!IS_ERR(m))
ns->mq_mnt = m;
spin_unlock(&mq_lock);
return m;
}
static struct dentry *mqueue_mount(struct file_system_type *fs_type,
int flags, const char *dev_name,
void *data)
{
struct ipc_namespace *ns;
if (flags & SB_KERNMOUNT) {
ns = data;
data = NULL;
} else {
ns = current->nsproxy->ipc_ns;
}
return mount_ns(fs_type, flags, data, ns, ns->user_ns, mqueue_fill_super);
struct vfsmount *m;
if (flags & SB_KERNMOUNT)
return mount_nodev(fs_type, flags, data, mqueue_fill_super);
m = mq_internal_mount();
if (IS_ERR(m))
return ERR_CAST(m);
atomic_inc(&m->mnt_sb->s_active);
down_write(&m->mnt_sb->s_umount);
return dget(m->mnt_root);
}
static void init_once(void *foo)
@ -743,13 +770,16 @@ static int prepare_open(struct dentry *dentry, int oflag, int ro,
static int do_mq_open(const char __user *u_name, int oflag, umode_t mode,
struct mq_attr *attr)
{
struct vfsmount *mnt = current->nsproxy->ipc_ns->mq_mnt;
struct dentry *root = mnt->mnt_root;
struct vfsmount *mnt = mq_internal_mount();
struct dentry *root;
struct filename *name;
struct path path;
int fd, error;
int ro;
if (IS_ERR(mnt))
return PTR_ERR(mnt);
audit_mq_open(oflag, mode, attr);
if (IS_ERR(name = getname(u_name)))
@ -760,6 +790,7 @@ static int do_mq_open(const char __user *u_name, int oflag, umode_t mode,
goto out_putname;
ro = mnt_want_write(mnt); /* we'll drop it in any case */
root = mnt->mnt_root;
inode_lock(d_inode(root));
path.dentry = lookup_one_len(name->name, root, strlen(name->name));
if (IS_ERR(path.dentry)) {
@ -808,6 +839,9 @@ SYSCALL_DEFINE1(mq_unlink, const char __user *, u_name)
struct ipc_namespace *ipc_ns = current->nsproxy->ipc_ns;
struct vfsmount *mnt = ipc_ns->mq_mnt;
if (!mnt)
return -ENOENT;
name = getname(u_name);
if (IS_ERR(name))
return PTR_ERR(name);
@ -1534,28 +1568,26 @@ int mq_init_ns(struct ipc_namespace *ns)
ns->mq_msgsize_max = DFLT_MSGSIZEMAX;
ns->mq_msg_default = DFLT_MSG;
ns->mq_msgsize_default = DFLT_MSGSIZE;
ns->mq_mnt = NULL;
ns->mq_mnt = kern_mount_data(&mqueue_fs_type, ns);
if (IS_ERR(ns->mq_mnt)) {
int err = PTR_ERR(ns->mq_mnt);
ns->mq_mnt = NULL;
return err;
}
return 0;
}
void mq_clear_sbinfo(struct ipc_namespace *ns)
{
ns->mq_mnt->mnt_sb->s_fs_info = NULL;
if (ns->mq_mnt)
ns->mq_mnt->mnt_sb->s_fs_info = NULL;
}
void mq_put_mnt(struct ipc_namespace *ns)
{
kern_unmount(ns->mq_mnt);
if (ns->mq_mnt)
kern_unmount(ns->mq_mnt);
}
static int __init init_mqueue_fs(void)
{
struct vfsmount *m;
int error;
mqueue_inode_cachep = kmem_cache_create("mqueue_inode_cache",
@ -1577,6 +1609,10 @@ static int __init init_mqueue_fs(void)
if (error)
goto out_filesystem;
m = kern_mount_data(&mqueue_fs_type, &init_ipc_ns);
if (IS_ERR(m))
goto out_filesystem;
init_ipc_ns.mq_mnt = m;
return 0;
out_filesystem: