Merge branch 'work.dcache' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull dcache_readdir() fixes from Al Viro: "The couple of patches you'd been OK with; no hlist conversion yet, and cursors are still in the list of children" [ Al is referring to future work to avoid some nasty O(n**2) behavior with the readdir cursors when you have lots of concurrent readdirs. This is just a fix for a race with a trivial cleanup - Linus ] * 'work.dcache' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: libfs: take cursors out of list when moving past the end of directory Fix the locking in dcache_readdir() and friends
This commit is contained in:
Linus Torvalds
commit
ad338d0543
129
fs/libfs.c
129
fs/libfs.c
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@ -89,58 +89,45 @@ int dcache_dir_close(struct inode *inode, struct file *file)
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EXPORT_SYMBOL(dcache_dir_close);
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/* parent is locked at least shared */
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static struct dentry *next_positive(struct dentry *parent,
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struct list_head *from,
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int count)
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/*
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* Returns an element of siblings' list.
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* We are looking for <count>th positive after <p>; if
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* found, dentry is grabbed and returned to caller.
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* If no such element exists, NULL is returned.
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*/
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static struct dentry *scan_positives(struct dentry *cursor,
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struct list_head *p,
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loff_t count,
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struct dentry *last)
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{
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unsigned *seq = &parent->d_inode->i_dir_seq, n;
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struct dentry *res;
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struct list_head *p;
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bool skipped;
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int i;
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struct dentry *dentry = cursor->d_parent, *found = NULL;
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retry:
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i = count;
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skipped = false;
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n = smp_load_acquire(seq) & ~1;
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res = NULL;
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rcu_read_lock();
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for (p = from->next; p != &parent->d_subdirs; p = p->next) {
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spin_lock(&dentry->d_lock);
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while ((p = p->next) != &dentry->d_subdirs) {
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struct dentry *d = list_entry(p, struct dentry, d_child);
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if (!simple_positive(d)) {
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skipped = true;
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} else if (!--i) {
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res = d;
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// we must at least skip cursors, to avoid livelocks
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if (d->d_flags & DCACHE_DENTRY_CURSOR)
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continue;
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if (simple_positive(d) && !--count) {
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spin_lock_nested(&d->d_lock, DENTRY_D_LOCK_NESTED);
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if (simple_positive(d))
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found = dget_dlock(d);
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spin_unlock(&d->d_lock);
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if (likely(found))
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break;
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count = 1;
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}
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if (need_resched()) {
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list_move(&cursor->d_child, p);
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p = &cursor->d_child;
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spin_unlock(&dentry->d_lock);
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cond_resched();
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spin_lock(&dentry->d_lock);
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}
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}
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rcu_read_unlock();
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if (skipped) {
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smp_rmb();
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if (unlikely(*seq != n))
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goto retry;
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}
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return res;
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}
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static void move_cursor(struct dentry *cursor, struct list_head *after)
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{
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struct dentry *parent = cursor->d_parent;
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unsigned n, *seq = &parent->d_inode->i_dir_seq;
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spin_lock(&parent->d_lock);
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for (;;) {
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n = *seq;
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if (!(n & 1) && cmpxchg(seq, n, n + 1) == n)
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break;
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cpu_relax();
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}
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__list_del(cursor->d_child.prev, cursor->d_child.next);
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if (after)
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list_add(&cursor->d_child, after);
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else
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list_add_tail(&cursor->d_child, &parent->d_subdirs);
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smp_store_release(seq, n + 2);
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spin_unlock(&parent->d_lock);
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spin_unlock(&dentry->d_lock);
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dput(last);
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return found;
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}
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loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence)
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@ -158,18 +145,26 @@ loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence)
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return -EINVAL;
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}
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if (offset != file->f_pos) {
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file->f_pos = offset;
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if (file->f_pos >= 2) {
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struct dentry *cursor = file->private_data;
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struct dentry *to;
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loff_t n = file->f_pos - 2;
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struct dentry *to = NULL;
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inode_lock_shared(dentry->d_inode);
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to = next_positive(dentry, &dentry->d_subdirs, n);
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move_cursor(cursor, to ? &to->d_child : NULL);
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if (offset > 2)
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to = scan_positives(cursor, &dentry->d_subdirs,
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offset - 2, NULL);
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spin_lock(&dentry->d_lock);
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if (to)
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list_move(&cursor->d_child, &to->d_child);
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else
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list_del_init(&cursor->d_child);
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spin_unlock(&dentry->d_lock);
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dput(to);
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file->f_pos = offset;
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inode_unlock_shared(dentry->d_inode);
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}
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}
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return offset;
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}
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EXPORT_SYMBOL(dcache_dir_lseek);
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@ -190,25 +185,35 @@ int dcache_readdir(struct file *file, struct dir_context *ctx)
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{
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struct dentry *dentry = file->f_path.dentry;
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struct dentry *cursor = file->private_data;
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struct list_head *p = &cursor->d_child;
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struct dentry *next;
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bool moved = false;
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struct list_head *anchor = &dentry->d_subdirs;
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struct dentry *next = NULL;
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struct list_head *p;
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if (!dir_emit_dots(file, ctx))
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return 0;
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if (ctx->pos == 2)
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p = &dentry->d_subdirs;
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while ((next = next_positive(dentry, p, 1)) != NULL) {
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p = anchor;
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else if (!list_empty(&cursor->d_child))
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p = &cursor->d_child;
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else
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return 0;
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while ((next = scan_positives(cursor, p, 1, next)) != NULL) {
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if (!dir_emit(ctx, next->d_name.name, next->d_name.len,
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d_inode(next)->i_ino, dt_type(d_inode(next))))
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break;
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moved = true;
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p = &next->d_child;
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ctx->pos++;
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p = &next->d_child;
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}
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if (moved)
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move_cursor(cursor, p);
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spin_lock(&dentry->d_lock);
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if (next)
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list_move_tail(&cursor->d_child, &next->d_child);
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else
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list_del_init(&cursor->d_child);
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spin_unlock(&dentry->d_lock);
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dput(next);
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return 0;
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}
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EXPORT_SYMBOL(dcache_readdir);
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