sanitize vfsmount refcounting changes
Instead of splitting refcount between (per-cpu) mnt_count and (SMP-only) mnt_longrefs, make all references contribute to mnt_count again and keep track of how many are longterm ones. Accounting rules for longterm count: * 1 for each fs_struct.root.mnt * 1 for each fs_struct.pwd.mnt * 1 for having non-NULL ->mnt_ns * decrement to 0 happens only under vfsmount lock exclusive That allows nice common case for mntput() - since we can't drop the final reference until after mnt_longterm has reached 0 due to the rules above, mntput() can grab vfsmount lock shared and check mnt_longterm. If it turns out to be non-zero (which is the common case), we know that this is not the final mntput() and can just blindly decrement percpu mnt_count. Otherwise we grab vfsmount lock exclusive and do usual decrement-and-check of percpu mnt_count. For fs_struct.c we have mnt_make_longterm() and mnt_make_shortterm(); namespace.c uses the latter in places where we don't already hold vfsmount lock exclusive and opencodes a few remaining spots where we need to manipulate mnt_longterm. Note that we mostly revert the code outside of fs/namespace.c back to what we used to have; in particular, normal code doesn't need to care about two kinds of references, etc. And we get to keep the optimization Nick's variant had bought us... Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
parent
7b8a53fd81
commit
f03c65993b
10 changed files with 75 additions and 117 deletions
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@ -1201,7 +1201,7 @@ static int __init init_mtdchar(void)
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static void __exit cleanup_mtdchar(void)
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{
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unregister_mtd_user(&mtdchar_notifier);
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mntput_long(mtd_inode_mnt);
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mntput(mtd_inode_mnt);
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unregister_filesystem(&mtd_inodefs_type);
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__unregister_chrdev(MTD_CHAR_MAJOR, 0, 1 << MINORBITS, "mtd");
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}
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@ -233,7 +233,7 @@ static int __init anon_inode_init(void)
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return 0;
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err_mntput:
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mntput_long(anon_inode_mnt);
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mntput(anon_inode_mnt);
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err_unregister_filesystem:
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unregister_filesystem(&anon_inode_fs_type);
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err_exit:
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@ -4,6 +4,19 @@
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#include <linux/path.h>
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#include <linux/slab.h>
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#include <linux/fs_struct.h>
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#include "internal.h"
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static inline void path_get_longterm(struct path *path)
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{
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path_get(path);
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mnt_make_longterm(path->mnt);
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}
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static inline void path_put_longterm(struct path *path)
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{
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mnt_make_shortterm(path->mnt);
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path_put(path);
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}
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/*
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* Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
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@ -17,11 +30,11 @@ void set_fs_root(struct fs_struct *fs, struct path *path)
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write_seqcount_begin(&fs->seq);
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old_root = fs->root;
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fs->root = *path;
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path_get_long(path);
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path_get_longterm(path);
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write_seqcount_end(&fs->seq);
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spin_unlock(&fs->lock);
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if (old_root.dentry)
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path_put_long(&old_root);
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path_put_longterm(&old_root);
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}
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/*
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@ -36,12 +49,12 @@ void set_fs_pwd(struct fs_struct *fs, struct path *path)
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write_seqcount_begin(&fs->seq);
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old_pwd = fs->pwd;
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fs->pwd = *path;
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path_get_long(path);
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path_get_longterm(path);
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write_seqcount_end(&fs->seq);
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spin_unlock(&fs->lock);
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if (old_pwd.dentry)
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path_put_long(&old_pwd);
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path_put_longterm(&old_pwd);
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}
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void chroot_fs_refs(struct path *old_root, struct path *new_root)
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@ -59,13 +72,13 @@ void chroot_fs_refs(struct path *old_root, struct path *new_root)
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write_seqcount_begin(&fs->seq);
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if (fs->root.dentry == old_root->dentry
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&& fs->root.mnt == old_root->mnt) {
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path_get_long(new_root);
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path_get_longterm(new_root);
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fs->root = *new_root;
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count++;
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}
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if (fs->pwd.dentry == old_root->dentry
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&& fs->pwd.mnt == old_root->mnt) {
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path_get_long(new_root);
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path_get_longterm(new_root);
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fs->pwd = *new_root;
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count++;
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}
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@ -76,13 +89,13 @@ void chroot_fs_refs(struct path *old_root, struct path *new_root)
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} while_each_thread(g, p);
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read_unlock(&tasklist_lock);
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while (count--)
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path_put_long(old_root);
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path_put_longterm(old_root);
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}
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void free_fs_struct(struct fs_struct *fs)
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{
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path_put_long(&fs->root);
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path_put_long(&fs->pwd);
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path_put_longterm(&fs->root);
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path_put_longterm(&fs->pwd);
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kmem_cache_free(fs_cachep, fs);
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}
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@ -118,9 +131,9 @@ struct fs_struct *copy_fs_struct(struct fs_struct *old)
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spin_lock(&old->lock);
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fs->root = old->root;
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path_get_long(&fs->root);
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path_get_longterm(&fs->root);
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fs->pwd = old->pwd;
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path_get_long(&fs->pwd);
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path_get_longterm(&fs->pwd);
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spin_unlock(&old->lock);
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}
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return fs;
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@ -73,6 +73,9 @@ extern struct vfsmount *copy_tree(struct vfsmount *, struct dentry *, int);
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extern int do_add_mount(struct vfsmount *, struct path *, int);
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extern void mnt_clear_expiry(struct vfsmount *);
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extern void mnt_make_longterm(struct vfsmount *);
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extern void mnt_make_shortterm(struct vfsmount *);
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extern void __init mnt_init(void);
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DECLARE_BRLOCK(vfsmount_lock);
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24
fs/namei.c
24
fs/namei.c
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@ -367,18 +367,6 @@ void path_get(struct path *path)
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}
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EXPORT_SYMBOL(path_get);
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/**
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* path_get_long - get a long reference to a path
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* @path: path to get the reference to
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*
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* Given a path increment the reference count to the dentry and the vfsmount.
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*/
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void path_get_long(struct path *path)
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{
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mntget_long(path->mnt);
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dget(path->dentry);
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}
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/**
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* path_put - put a reference to a path
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* @path: path to put the reference to
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@ -392,18 +380,6 @@ void path_put(struct path *path)
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}
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EXPORT_SYMBOL(path_put);
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/**
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* path_put_long - put a long reference to a path
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* @path: path to put the reference to
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*
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* Given a path decrement the reference count to the dentry and the vfsmount.
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*/
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void path_put_long(struct path *path)
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{
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dput(path->dentry);
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mntput_long(path->mnt);
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}
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/**
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* nameidata_drop_rcu - drop this nameidata out of rcu-walk
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* @nd: nameidata pathwalk data to drop
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116
fs/namespace.c
116
fs/namespace.c
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@ -183,7 +183,7 @@ static inline void mnt_dec_count(struct vfsmount *mnt)
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unsigned int mnt_get_count(struct vfsmount *mnt)
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{
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#ifdef CONFIG_SMP
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unsigned int count = atomic_read(&mnt->mnt_longrefs);
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unsigned int count = 0;
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int cpu;
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for_each_possible_cpu(cpu) {
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@ -217,7 +217,7 @@ struct vfsmount *alloc_vfsmnt(const char *name)
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if (!mnt->mnt_pcp)
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goto out_free_devname;
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atomic_set(&mnt->mnt_longrefs, 1);
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this_cpu_add(mnt->mnt_pcp->mnt_count, 1);
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#else
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mnt->mnt_count = 1;
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mnt->mnt_writers = 0;
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@ -624,8 +624,11 @@ static void commit_tree(struct vfsmount *mnt)
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BUG_ON(parent == mnt);
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list_add_tail(&head, &mnt->mnt_list);
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list_for_each_entry(m, &head, mnt_list)
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list_for_each_entry(m, &head, mnt_list) {
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m->mnt_ns = n;
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atomic_inc(&m->mnt_longterm);
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}
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list_splice(&head, n->list.prev);
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list_add_tail(&mnt->mnt_hash, mount_hashtable +
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@ -734,51 +737,30 @@ static inline void mntfree(struct vfsmount *mnt)
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deactivate_super(sb);
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}
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#ifdef CONFIG_SMP
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static inline void __mntput(struct vfsmount *mnt, int longrefs)
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static void mntput_no_expire(struct vfsmount *mnt)
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{
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if (!longrefs) {
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put_again:
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br_read_lock(vfsmount_lock);
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if (likely(atomic_read(&mnt->mnt_longrefs))) {
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mnt_dec_count(mnt);
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br_read_unlock(vfsmount_lock);
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return;
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}
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#ifdef CONFIG_SMP
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br_read_lock(vfsmount_lock);
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if (likely(atomic_read(&mnt->mnt_longterm))) {
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mnt_dec_count(mnt);
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br_read_unlock(vfsmount_lock);
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} else {
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BUG_ON(!atomic_read(&mnt->mnt_longrefs));
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if (atomic_add_unless(&mnt->mnt_longrefs, -1, 1))
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return;
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return;
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}
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br_read_unlock(vfsmount_lock);
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br_write_lock(vfsmount_lock);
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if (!longrefs)
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mnt_dec_count(mnt);
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else
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atomic_dec(&mnt->mnt_longrefs);
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mnt_dec_count(mnt);
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if (mnt_get_count(mnt)) {
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br_write_unlock(vfsmount_lock);
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return;
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}
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if (unlikely(mnt->mnt_pinned)) {
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mnt_add_count(mnt, mnt->mnt_pinned + 1);
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mnt->mnt_pinned = 0;
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br_write_unlock(vfsmount_lock);
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acct_auto_close_mnt(mnt);
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goto put_again;
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}
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br_write_unlock(vfsmount_lock);
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mntfree(mnt);
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}
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#else
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static inline void __mntput(struct vfsmount *mnt, int longrefs)
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{
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put_again:
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mnt_dec_count(mnt);
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if (likely(mnt_get_count(mnt)))
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return;
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br_write_lock(vfsmount_lock);
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#endif
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if (unlikely(mnt->mnt_pinned)) {
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mnt_add_count(mnt, mnt->mnt_pinned + 1);
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mnt->mnt_pinned = 0;
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br_write_unlock(vfsmount_lock);
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mntfree(mnt);
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}
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#endif
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static void mntput_no_expire(struct vfsmount *mnt)
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{
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__mntput(mnt, 0);
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}
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void mntput(struct vfsmount *mnt)
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{
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/* avoid cacheline pingpong, hope gcc doesn't get "smart" */
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if (unlikely(mnt->mnt_expiry_mark))
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mnt->mnt_expiry_mark = 0;
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__mntput(mnt, 0);
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mntput_no_expire(mnt);
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}
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}
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EXPORT_SYMBOL(mntput);
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@ -815,33 +791,6 @@ struct vfsmount *mntget(struct vfsmount *mnt)
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}
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EXPORT_SYMBOL(mntget);
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void mntput_long(struct vfsmount *mnt)
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{
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#ifdef CONFIG_SMP
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if (mnt) {
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/* avoid cacheline pingpong, hope gcc doesn't get "smart" */
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if (unlikely(mnt->mnt_expiry_mark))
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mnt->mnt_expiry_mark = 0;
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__mntput(mnt, 1);
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}
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#else
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mntput(mnt);
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#endif
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}
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EXPORT_SYMBOL(mntput_long);
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struct vfsmount *mntget_long(struct vfsmount *mnt)
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{
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#ifdef CONFIG_SMP
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if (mnt)
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atomic_inc(&mnt->mnt_longrefs);
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return mnt;
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#else
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return mntget(mnt);
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#endif
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}
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EXPORT_SYMBOL(mntget_long);
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void mnt_pin(struct vfsmount *mnt)
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{
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br_write_lock(vfsmount_lock);
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@ -1216,7 +1165,7 @@ void release_mounts(struct list_head *head)
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dput(dentry);
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mntput(m);
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}
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mntput_long(mnt);
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mntput(mnt);
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}
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}
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@ -1240,6 +1189,7 @@ void umount_tree(struct vfsmount *mnt, int propagate, struct list_head *kill)
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list_del_init(&p->mnt_list);
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__touch_mnt_namespace(p->mnt_ns);
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p->mnt_ns = NULL;
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atomic_dec(&p->mnt_longterm);
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list_del_init(&p->mnt_child);
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if (p->mnt_parent != p) {
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p->mnt_parent->mnt_ghosts++;
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@ -1969,7 +1919,7 @@ int do_add_mount(struct vfsmount *newmnt, struct path *path, int mnt_flags)
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unlock:
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up_write(&namespace_sem);
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mntput_long(newmnt);
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mntput(newmnt);
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return err;
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}
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@ -2291,6 +2241,20 @@ static struct mnt_namespace *alloc_mnt_ns(void)
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return new_ns;
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}
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void mnt_make_longterm(struct vfsmount *mnt)
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{
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atomic_inc(&mnt->mnt_longterm);
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}
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void mnt_make_shortterm(struct vfsmount *mnt)
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{
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if (atomic_add_unless(&mnt->mnt_longterm, -1, 1))
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return;
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br_write_lock(vfsmount_lock);
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atomic_dec(&mnt->mnt_longterm);
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br_write_unlock(vfsmount_lock);
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}
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/*
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* Allocate a new namespace structure and populate it with contents
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* copied from the namespace of the passed in task structure.
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@ -2328,14 +2292,19 @@ static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,
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q = new_ns->root;
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while (p) {
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q->mnt_ns = new_ns;
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atomic_inc(&q->mnt_longterm);
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if (fs) {
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if (p == fs->root.mnt) {
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fs->root.mnt = mntget(q);
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atomic_inc(&q->mnt_longterm);
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mnt_make_shortterm(p);
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rootmnt = p;
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fs->root.mnt = mntget_long(q);
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}
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if (p == fs->pwd.mnt) {
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fs->pwd.mnt = mntget(q);
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atomic_inc(&q->mnt_longterm);
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mnt_make_shortterm(p);
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pwdmnt = p;
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fs->pwd.mnt = mntget_long(q);
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}
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}
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p = next_mnt(p, mnt_ns->root);
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@ -2344,9 +2313,9 @@ static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,
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up_write(&namespace_sem);
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if (rootmnt)
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mntput_long(rootmnt);
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mntput(rootmnt);
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if (pwdmnt)
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mntput_long(pwdmnt);
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mntput(pwdmnt);
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return new_ns;
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}
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@ -2379,6 +2348,7 @@ struct mnt_namespace *create_mnt_ns(struct vfsmount *mnt)
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new_ns = alloc_mnt_ns();
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if (!IS_ERR(new_ns)) {
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mnt->mnt_ns = new_ns;
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atomic_inc(&mnt->mnt_longterm);
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new_ns->root = mnt;
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list_add(&new_ns->list, &new_ns->root->mnt_list);
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}
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|
|
|
@ -1292,7 +1292,7 @@ static int __init init_pipe_fs(void)
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static void __exit exit_pipe_fs(void)
|
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{
|
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unregister_filesystem(&pipe_fs_type);
|
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mntput_long(pipe_mnt);
|
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mntput(pipe_mnt);
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}
|
||||
|
||||
fs_initcall(init_pipe_fs);
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|
|
|
@ -1141,7 +1141,7 @@ static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
|
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return mnt;
|
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|
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err:
|
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mntput_long(mnt);
|
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mntput(mnt);
|
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return ERR_PTR(err);
|
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}
|
||||
|
||||
|
|
|
@ -60,7 +60,7 @@ struct vfsmount {
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|||
struct super_block *mnt_sb; /* pointer to superblock */
|
||||
#ifdef CONFIG_SMP
|
||||
struct mnt_pcp __percpu *mnt_pcp;
|
||||
atomic_t mnt_longrefs;
|
||||
atomic_t mnt_longterm; /* how many of the refs are longterm */
|
||||
#else
|
||||
int mnt_count;
|
||||
int mnt_writers;
|
||||
|
@ -96,8 +96,6 @@ extern int mnt_clone_write(struct vfsmount *mnt);
|
|||
extern void mnt_drop_write(struct vfsmount *mnt);
|
||||
extern void mntput(struct vfsmount *mnt);
|
||||
extern struct vfsmount *mntget(struct vfsmount *mnt);
|
||||
extern void mntput_long(struct vfsmount *mnt);
|
||||
extern struct vfsmount *mntget_long(struct vfsmount *mnt);
|
||||
extern void mnt_pin(struct vfsmount *mnt);
|
||||
extern void mnt_unpin(struct vfsmount *mnt);
|
||||
extern int __mnt_is_readonly(struct vfsmount *mnt);
|
||||
|
|
|
@ -10,9 +10,7 @@ struct path {
|
|||
};
|
||||
|
||||
extern void path_get(struct path *);
|
||||
extern void path_get_long(struct path *);
|
||||
extern void path_put(struct path *);
|
||||
extern void path_put_long(struct path *);
|
||||
|
||||
static inline int path_equal(const struct path *path1, const struct path *path2)
|
||||
{
|
||||
|
|
Loading…
Reference in a new issue