sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 368 insertions, 0 deletions

diff --git a/fs/efs/super.c b/fs/efs/super.c
new file mode 100644
index 000000000..11fea3bbc
--- /dev/null
+++ b/fs/efs/super.c
@@ -0,0 +1,368 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * super.c
+ *
+ * Copyright (c) 1999 Al Smith
+ *
+ * Portions derived from work (c) 1995,1996 Christian Vogelgsang.
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/exportfs.h>
+#include <linux/slab.h>
+#include <linux/buffer_head.h>
+#include <linux/vfs.h>
+#include <linux/blkdev.h>
+#include <linux/fs_context.h>
+#include "efs.h"
+#include <linux/efs_vh.h>
+#include <linux/efs_fs_sb.h>
+
+static int efs_statfs(struct dentry *dentry, struct kstatfs *buf);
+static int efs_init_fs_context(struct fs_context *fc);
+
+static void efs_kill_sb(struct super_block *s)
+{
+	struct efs_sb_info *sbi = SUPER_INFO(s);
+	kill_block_super(s);
+	kfree(sbi);
+}
+
+static struct pt_types sgi_pt_types[] = {
+	{0x00,		"SGI vh"},
+	{0x01,		"SGI trkrepl"},
+	{0x02,		"SGI secrepl"},
+	{0x03,		"SGI raw"},
+	{0x04,		"SGI bsd"},
+	{SGI_SYSV,	"SGI sysv"},
+	{0x06,		"SGI vol"},
+	{SGI_EFS,	"SGI efs"},
+	{0x08,		"SGI lv"},
+	{0x09,		"SGI rlv"},
+	{0x0A,		"SGI xfs"},
+	{0x0B,		"SGI xfslog"},
+	{0x0C,		"SGI xlv"},
+	{0x82,		"Linux swap"},
+	{0x83,		"Linux native"},
+	{0,		NULL}
+};
+
+/*
+ * File system definition and registration.
+ */
+static struct file_system_type efs_fs_type = {
+	.owner			= THIS_MODULE,
+	.name			= "efs",
+	.kill_sb		= efs_kill_sb,
+	.fs_flags		= FS_REQUIRES_DEV,
+	.init_fs_context	= efs_init_fs_context,
+};
+MODULE_ALIAS_FS("efs");
+
+static struct kmem_cache * efs_inode_cachep;
+
+static struct inode *efs_alloc_inode(struct super_block *sb)
+{
+	struct efs_inode_info *ei;
+	ei = alloc_inode_sb(sb, efs_inode_cachep, GFP_KERNEL);
+	if (!ei)
+		return NULL;
+	return &ei->vfs_inode;
+}
+
+static void efs_free_inode(struct inode *inode)
+{
+	kmem_cache_free(efs_inode_cachep, INODE_INFO(inode));
+}
+
+static void init_once(void *foo)
+{
+	struct efs_inode_info *ei = (struct efs_inode_info *) foo;
+
+	inode_init_once(&ei->vfs_inode);
+}
+
+static int __init init_inodecache(void)
+{
+	efs_inode_cachep = kmem_cache_create("efs_inode_cache",
+				sizeof(struct efs_inode_info), 0,
+				SLAB_RECLAIM_ACCOUNT|SLAB_ACCOUNT,
+				init_once);
+	if (efs_inode_cachep == NULL)
+		return -ENOMEM;
+	return 0;
+}
+
+static void destroy_inodecache(void)
+{
+	/*
+	 * Make sure all delayed rcu free inodes are flushed before we
+	 * destroy cache.
+	 */
+	rcu_barrier();
+	kmem_cache_destroy(efs_inode_cachep);
+}
+
+static const struct super_operations efs_superblock_operations = {
+	.alloc_inode	= efs_alloc_inode,
+	.free_inode	= efs_free_inode,
+	.statfs		= efs_statfs,
+};
+
+static const struct export_operations efs_export_ops = {
+	.encode_fh	= generic_encode_ino32_fh,
+	.fh_to_dentry	= efs_fh_to_dentry,
+	.fh_to_parent	= efs_fh_to_parent,
+	.get_parent	= efs_get_parent,
+};
+
+static int __init init_efs_fs(void) {
+	int err;
+	pr_info(EFS_VERSION" - http://aeschi.ch.eu.org/efs/\n");
+	err = init_inodecache();
+	if (err)
+		goto out1;
+	err = register_filesystem(&efs_fs_type);
+	if (err)
+		goto out;
+	return 0;
+out:
+	destroy_inodecache();
+out1:
+	return err;
+}
+
+static void __exit exit_efs_fs(void) {
+	unregister_filesystem(&efs_fs_type);
+	destroy_inodecache();
+}
+
+module_init(init_efs_fs)
+module_exit(exit_efs_fs)
+
+static efs_block_t efs_validate_vh(struct volume_header *vh) {
+	int		i;
+	__be32		cs, *ui;
+	int		csum;
+	efs_block_t	sblock = 0; /* shuts up gcc */
+	struct pt_types	*pt_entry;
+	int		pt_type, slice = -1;
+
+	if (be32_to_cpu(vh->vh_magic) != VHMAGIC) {
+		/*
+		 * assume that we're dealing with a partition and allow
+		 * read_super() to try and detect a valid superblock
+		 * on the next block.
+		 */
+		return 0;
+	}
+
+	ui = ((__be32 *) (vh + 1)) - 1;
+	for(csum = 0; ui >= ((__be32 *) vh);) {
+		cs = *ui--;
+		csum += be32_to_cpu(cs);
+	}
+	if (csum) {
+		pr_warn("SGI disklabel: checksum bad, label corrupted\n");
+		return 0;
+	}
+
+#ifdef DEBUG
+	pr_debug("bf: \"%16s\"\n", vh->vh_bootfile);
+
+	for(i = 0; i < NVDIR; i++) {
+		int	j;
+		char	name[VDNAMESIZE+1];
+
+		for(j = 0; j < VDNAMESIZE; j++) {
+			name[j] = vh->vh_vd[i].vd_name[j];
+		}
+		name[j] = (char) 0;
+
+		if (name[0]) {
+			pr_debug("vh: %8s block: 0x%08x size: 0x%08x\n",
+				name, (int) be32_to_cpu(vh->vh_vd[i].vd_lbn),
+				(int) be32_to_cpu(vh->vh_vd[i].vd_nbytes));
+		}
+	}
+#endif
+
+	for(i = 0; i < NPARTAB; i++) {
+		pt_type = (int) be32_to_cpu(vh->vh_pt[i].pt_type);
+		for(pt_entry = sgi_pt_types; pt_entry->pt_name; pt_entry++) {
+			if (pt_type == pt_entry->pt_type) break;
+		}
+#ifdef DEBUG
+		if (be32_to_cpu(vh->vh_pt[i].pt_nblks)) {
+			pr_debug("pt %2d: start: %08d size: %08d type: 0x%02x (%s)\n",
+				 i, (int)be32_to_cpu(vh->vh_pt[i].pt_firstlbn),
+				 (int)be32_to_cpu(vh->vh_pt[i].pt_nblks),
+				 pt_type, (pt_entry->pt_name) ?
+				 pt_entry->pt_name : "unknown");
+		}
+#endif
+		if (IS_EFS(pt_type)) {
+			sblock = be32_to_cpu(vh->vh_pt[i].pt_firstlbn);
+			slice = i;
+		}
+	}
+
+	if (slice == -1) {
+		pr_notice("partition table contained no EFS partitions\n");
+#ifdef DEBUG
+	} else {
+		pr_info("using slice %d (type %s, offset 0x%x)\n", slice,
+			(pt_entry->pt_name) ? pt_entry->pt_name : "unknown",
+			sblock);
+#endif
+	}
+	return sblock;
+}
+
+static int efs_validate_super(struct efs_sb_info *sb, struct efs_super *super) {
+
+	if (!IS_EFS_MAGIC(be32_to_cpu(super->fs_magic)))
+		return -1;
+
+	sb->fs_magic     = be32_to_cpu(super->fs_magic);
+	sb->total_blocks = be32_to_cpu(super->fs_size);
+	sb->first_block  = be32_to_cpu(super->fs_firstcg);
+	sb->group_size   = be32_to_cpu(super->fs_cgfsize);
+	sb->data_free    = be32_to_cpu(super->fs_tfree);
+	sb->inode_free   = be32_to_cpu(super->fs_tinode);
+	sb->inode_blocks = be16_to_cpu(super->fs_cgisize);
+	sb->total_groups = be16_to_cpu(super->fs_ncg);
+    
+	return 0;    
+}
+
+static int efs_fill_super(struct super_block *s, struct fs_context *fc)
+{
+	struct efs_sb_info *sb;
+	struct buffer_head *bh;
+	struct inode *root;
+
+	sb = kzalloc_obj(struct efs_sb_info);
+	if (!sb)
+		return -ENOMEM;
+	s->s_fs_info = sb;
+	s->s_time_min = 0;
+	s->s_time_max = U32_MAX;
+
+	s->s_magic		= EFS_SUPER_MAGIC;
+	if (!sb_set_blocksize(s, EFS_BLOCKSIZE)) {
+		pr_err("device does not support %d byte blocks\n",
+			EFS_BLOCKSIZE);
+		return invalf(fc, "device does not support %d byte blocks\n",
+			      EFS_BLOCKSIZE);
+	}
+
+	/* read the vh (volume header) block */
+	bh = sb_bread(s, 0);
+
+	if (!bh) {
+		pr_err("cannot read volume header\n");
+		return -EIO;
+	}
+
+	/*
+	 * if this returns zero then we didn't find any partition table.
+	 * this isn't (yet) an error - just assume for the moment that
+	 * the device is valid and go on to search for a superblock.
+	 */
+	sb->fs_start = efs_validate_vh((struct volume_header *) bh->b_data);
+	brelse(bh);
+
+	if (sb->fs_start == -1) {
+		return -EINVAL;
+	}
+
+	bh = sb_bread(s, sb->fs_start + EFS_SUPER);
+	if (!bh) {
+		pr_err("cannot read superblock\n");
+		return -EIO;
+	}
+
+	if (efs_validate_super(sb, (struct efs_super *) bh->b_data)) {
+#ifdef DEBUG
+		pr_warn("invalid superblock at block %u\n",
+			sb->fs_start + EFS_SUPER);
+#endif
+		brelse(bh);
+		return -EINVAL;
+	}
+	brelse(bh);
+
+	if (!sb_rdonly(s)) {
+#ifdef DEBUG
+		pr_info("forcing read-only mode\n");
+#endif
+		s->s_flags |= SB_RDONLY;
+	}
+	s->s_op   = &efs_superblock_operations;
+	s->s_export_op = &efs_export_ops;
+	root = efs_iget(s, EFS_ROOTINODE);
+	if (IS_ERR(root)) {
+		pr_err("get root inode failed\n");
+		return PTR_ERR(root);
+	}
+
+	s->s_root = d_make_root(root);
+	if (!(s->s_root)) {
+		pr_err("get root dentry failed\n");
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
+static int efs_get_tree(struct fs_context *fc)
+{
+	return get_tree_bdev(fc, efs_fill_super);
+}
+
+static int efs_reconfigure(struct fs_context *fc)
+{
+	sync_filesystem(fc->root->d_sb);
+	fc->sb_flags |= SB_RDONLY;
+
+	return 0;
+}
+
+static const struct fs_context_operations efs_context_opts = {
+	.get_tree	= efs_get_tree,
+	.reconfigure	= efs_reconfigure,
+};
+
+/*
+ * Set up the filesystem mount context.
+ */
+static int efs_init_fs_context(struct fs_context *fc)
+{
+	fc->ops = &efs_context_opts;
+
+	return 0;
+}
+
+static int efs_statfs(struct dentry *dentry, struct kstatfs *buf) {
+	struct super_block *sb = dentry->d_sb;
+	struct efs_sb_info *sbi = SUPER_INFO(sb);
+	u64 id = huge_encode_dev(sb->s_bdev->bd_dev);
+
+	buf->f_type    = EFS_SUPER_MAGIC;	/* efs magic number */
+	buf->f_bsize   = EFS_BLOCKSIZE;		/* blocksize */
+	buf->f_blocks  = sbi->total_groups *	/* total data blocks */
+			(sbi->group_size - sbi->inode_blocks);
+	buf->f_bfree   = sbi->data_free;	/* free data blocks */
+	buf->f_bavail  = sbi->data_free;	/* free blocks for non-root */
+	buf->f_files   = sbi->total_groups *	/* total inodes */
+			sbi->inode_blocks *
+			(EFS_BLOCKSIZE / sizeof(struct efs_dinode));
+	buf->f_ffree   = sbi->inode_free;	/* free inodes */
+	buf->f_fsid    = u64_to_fsid(id);
+	buf->f_namelen = EFS_MAXNAMELEN;	/* max filename length */
+
+	return 0;
+}
+