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99b7db7b8f
fs: brlock vfsmount_lock Use a brlock for the vfsmount lock. It must be taken for write whenever modifying the mount hash or associated fields, and may be taken for read when performing mount hash lookups. A new lock is added for the mnt-id allocator, so it doesn't need to take the heavy vfsmount write-lock. The number of atomics should remain the same for fastpath rlock cases, though code would be slightly slower due to per-cpu access. Scalability is not not be much improved in common cases yet, due to other locks (ie. dcache_lock) getting in the way. However path lookups crossing mountpoints should be one case where scalability is improved (currently requiring the global lock). The slowpath is slower due to use of brlock. On a 64 core, 64 socket, 32 node Altix system (high latency to remote nodes), a simple umount microbenchmark (mount --bind mnt mnt2 ; umount mnt2 loop 1000 times), before this patch it took 6.8s, afterwards took 7.1s, about 5% slower. Cc: Al Viro <viro@ZenIV.linux.org.uk> Signed-off-by: Nick Piggin <npiggin@kernel.dk> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
372 lines
9.3 KiB
C
372 lines
9.3 KiB
C
/*
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* linux/fs/pnode.c
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*
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* (C) Copyright IBM Corporation 2005.
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* Released under GPL v2.
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* Author : Ram Pai (linuxram@us.ibm.com)
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*
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*/
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#include <linux/mnt_namespace.h>
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#include <linux/mount.h>
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#include <linux/fs.h>
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#include "internal.h"
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#include "pnode.h"
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/* return the next shared peer mount of @p */
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static inline struct vfsmount *next_peer(struct vfsmount *p)
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{
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return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
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}
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static inline struct vfsmount *first_slave(struct vfsmount *p)
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{
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return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave);
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}
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static inline struct vfsmount *next_slave(struct vfsmount *p)
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{
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return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave);
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}
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/*
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* Return true if path is reachable from root
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*
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* namespace_sem is held, and mnt is attached
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*/
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static bool is_path_reachable(struct vfsmount *mnt, struct dentry *dentry,
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const struct path *root)
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{
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while (mnt != root->mnt && mnt->mnt_parent != mnt) {
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dentry = mnt->mnt_mountpoint;
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mnt = mnt->mnt_parent;
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}
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return mnt == root->mnt && is_subdir(dentry, root->dentry);
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}
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static struct vfsmount *get_peer_under_root(struct vfsmount *mnt,
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struct mnt_namespace *ns,
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const struct path *root)
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{
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struct vfsmount *m = mnt;
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do {
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/* Check the namespace first for optimization */
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if (m->mnt_ns == ns && is_path_reachable(m, m->mnt_root, root))
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return m;
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m = next_peer(m);
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} while (m != mnt);
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return NULL;
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}
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/*
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* Get ID of closest dominating peer group having a representative
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* under the given root.
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*
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* Caller must hold namespace_sem
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*/
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int get_dominating_id(struct vfsmount *mnt, const struct path *root)
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{
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struct vfsmount *m;
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for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
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struct vfsmount *d = get_peer_under_root(m, mnt->mnt_ns, root);
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if (d)
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return d->mnt_group_id;
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}
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return 0;
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}
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static int do_make_slave(struct vfsmount *mnt)
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{
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struct vfsmount *peer_mnt = mnt, *master = mnt->mnt_master;
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struct vfsmount *slave_mnt;
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/*
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* slave 'mnt' to a peer mount that has the
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* same root dentry. If none is available then
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* slave it to anything that is available.
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*/
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while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
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peer_mnt->mnt_root != mnt->mnt_root) ;
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if (peer_mnt == mnt) {
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peer_mnt = next_peer(mnt);
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if (peer_mnt == mnt)
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peer_mnt = NULL;
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}
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if (IS_MNT_SHARED(mnt) && list_empty(&mnt->mnt_share))
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mnt_release_group_id(mnt);
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list_del_init(&mnt->mnt_share);
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mnt->mnt_group_id = 0;
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if (peer_mnt)
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master = peer_mnt;
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if (master) {
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list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
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slave_mnt->mnt_master = master;
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list_move(&mnt->mnt_slave, &master->mnt_slave_list);
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list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
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INIT_LIST_HEAD(&mnt->mnt_slave_list);
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} else {
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struct list_head *p = &mnt->mnt_slave_list;
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while (!list_empty(p)) {
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slave_mnt = list_first_entry(p,
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struct vfsmount, mnt_slave);
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list_del_init(&slave_mnt->mnt_slave);
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slave_mnt->mnt_master = NULL;
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}
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}
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mnt->mnt_master = master;
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CLEAR_MNT_SHARED(mnt);
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return 0;
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}
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/*
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* vfsmount lock must be held for write
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*/
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void change_mnt_propagation(struct vfsmount *mnt, int type)
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{
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if (type == MS_SHARED) {
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set_mnt_shared(mnt);
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return;
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}
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do_make_slave(mnt);
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if (type != MS_SLAVE) {
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list_del_init(&mnt->mnt_slave);
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mnt->mnt_master = NULL;
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if (type == MS_UNBINDABLE)
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mnt->mnt_flags |= MNT_UNBINDABLE;
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else
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mnt->mnt_flags &= ~MNT_UNBINDABLE;
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}
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}
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/*
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* get the next mount in the propagation tree.
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* @m: the mount seen last
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* @origin: the original mount from where the tree walk initiated
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*
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* Note that peer groups form contiguous segments of slave lists.
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* We rely on that in get_source() to be able to find out if
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* vfsmount found while iterating with propagation_next() is
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* a peer of one we'd found earlier.
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*/
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static struct vfsmount *propagation_next(struct vfsmount *m,
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struct vfsmount *origin)
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{
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/* are there any slaves of this mount? */
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if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
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return first_slave(m);
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while (1) {
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struct vfsmount *next;
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struct vfsmount *master = m->mnt_master;
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if (master == origin->mnt_master) {
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next = next_peer(m);
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return ((next == origin) ? NULL : next);
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} else if (m->mnt_slave.next != &master->mnt_slave_list)
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return next_slave(m);
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/* back at master */
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m = master;
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}
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}
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/*
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* return the source mount to be used for cloning
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*
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* @dest the current destination mount
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* @last_dest the last seen destination mount
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* @last_src the last seen source mount
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* @type return CL_SLAVE if the new mount has to be
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* cloned as a slave.
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*/
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static struct vfsmount *get_source(struct vfsmount *dest,
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struct vfsmount *last_dest,
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struct vfsmount *last_src,
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int *type)
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{
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struct vfsmount *p_last_src = NULL;
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struct vfsmount *p_last_dest = NULL;
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while (last_dest != dest->mnt_master) {
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p_last_dest = last_dest;
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p_last_src = last_src;
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last_dest = last_dest->mnt_master;
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last_src = last_src->mnt_master;
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}
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if (p_last_dest) {
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do {
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p_last_dest = next_peer(p_last_dest);
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} while (IS_MNT_NEW(p_last_dest));
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/* is that a peer of the earlier? */
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if (dest == p_last_dest) {
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*type = CL_MAKE_SHARED;
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return p_last_src;
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}
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}
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/* slave of the earlier, then */
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*type = CL_SLAVE;
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/* beginning of peer group among the slaves? */
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if (IS_MNT_SHARED(dest))
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*type |= CL_MAKE_SHARED;
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return last_src;
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}
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/*
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* mount 'source_mnt' under the destination 'dest_mnt' at
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* dentry 'dest_dentry'. And propagate that mount to
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* all the peer and slave mounts of 'dest_mnt'.
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* Link all the new mounts into a propagation tree headed at
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* source_mnt. Also link all the new mounts using ->mnt_list
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* headed at source_mnt's ->mnt_list
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*
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* @dest_mnt: destination mount.
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* @dest_dentry: destination dentry.
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* @source_mnt: source mount.
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* @tree_list : list of heads of trees to be attached.
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*/
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int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry,
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struct vfsmount *source_mnt, struct list_head *tree_list)
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{
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struct vfsmount *m, *child;
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int ret = 0;
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struct vfsmount *prev_dest_mnt = dest_mnt;
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struct vfsmount *prev_src_mnt = source_mnt;
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LIST_HEAD(tmp_list);
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LIST_HEAD(umount_list);
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for (m = propagation_next(dest_mnt, dest_mnt); m;
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m = propagation_next(m, dest_mnt)) {
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int type;
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struct vfsmount *source;
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if (IS_MNT_NEW(m))
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continue;
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source = get_source(m, prev_dest_mnt, prev_src_mnt, &type);
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if (!(child = copy_tree(source, source->mnt_root, type))) {
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ret = -ENOMEM;
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list_splice(tree_list, tmp_list.prev);
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goto out;
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}
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if (is_subdir(dest_dentry, m->mnt_root)) {
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mnt_set_mountpoint(m, dest_dentry, child);
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list_add_tail(&child->mnt_hash, tree_list);
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} else {
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/*
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* This can happen if the parent mount was bind mounted
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* on some subdirectory of a shared/slave mount.
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*/
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list_add_tail(&child->mnt_hash, &tmp_list);
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}
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prev_dest_mnt = m;
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prev_src_mnt = child;
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}
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out:
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br_write_lock(vfsmount_lock);
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while (!list_empty(&tmp_list)) {
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child = list_first_entry(&tmp_list, struct vfsmount, mnt_hash);
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umount_tree(child, 0, &umount_list);
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}
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br_write_unlock(vfsmount_lock);
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release_mounts(&umount_list);
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return ret;
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}
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/*
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* return true if the refcount is greater than count
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*/
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static inline int do_refcount_check(struct vfsmount *mnt, int count)
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{
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int mycount = atomic_read(&mnt->mnt_count) - mnt->mnt_ghosts;
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return (mycount > count);
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}
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/*
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* check if the mount 'mnt' can be unmounted successfully.
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* @mnt: the mount to be checked for unmount
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* NOTE: unmounting 'mnt' would naturally propagate to all
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* other mounts its parent propagates to.
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* Check if any of these mounts that **do not have submounts**
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* have more references than 'refcnt'. If so return busy.
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*
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* vfsmount lock must be held for read or write
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*/
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int propagate_mount_busy(struct vfsmount *mnt, int refcnt)
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{
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struct vfsmount *m, *child;
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struct vfsmount *parent = mnt->mnt_parent;
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int ret = 0;
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if (mnt == parent)
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return do_refcount_check(mnt, refcnt);
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/*
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* quickly check if the current mount can be unmounted.
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* If not, we don't have to go checking for all other
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* mounts
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*/
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if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
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return 1;
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for (m = propagation_next(parent, parent); m;
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m = propagation_next(m, parent)) {
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child = __lookup_mnt(m, mnt->mnt_mountpoint, 0);
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if (child && list_empty(&child->mnt_mounts) &&
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(ret = do_refcount_check(child, 1)))
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break;
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}
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return ret;
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}
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/*
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* NOTE: unmounting 'mnt' naturally propagates to all other mounts its
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* parent propagates to.
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*/
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static void __propagate_umount(struct vfsmount *mnt)
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{
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struct vfsmount *parent = mnt->mnt_parent;
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struct vfsmount *m;
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BUG_ON(parent == mnt);
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for (m = propagation_next(parent, parent); m;
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m = propagation_next(m, parent)) {
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struct vfsmount *child = __lookup_mnt(m,
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mnt->mnt_mountpoint, 0);
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/*
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* umount the child only if the child has no
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* other children
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*/
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if (child && list_empty(&child->mnt_mounts))
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list_move_tail(&child->mnt_hash, &mnt->mnt_hash);
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}
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}
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/*
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* collect all mounts that receive propagation from the mount in @list,
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* and return these additional mounts in the same list.
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* @list: the list of mounts to be unmounted.
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*
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* vfsmount lock must be held for write
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*/
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int propagate_umount(struct list_head *list)
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{
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struct vfsmount *mnt;
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list_for_each_entry(mnt, list, mnt_hash)
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__propagate_umount(mnt);
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return 0;
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}
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