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, 390 insertions, 0 deletions

diff --git a/fs/fs_parser.c b/fs/fs_parser.c
new file mode 100644
index 000000000..b4cc4cce5
--- /dev/null
+++ b/fs/fs_parser.c
@@ -0,0 +1,390 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Filesystem parameter parser.
+ *
+ * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/export.h>
+#include <linux/fs_context.h>
+#include <linux/fs_parser.h>
+#include <linux/slab.h>
+#include <linux/security.h>
+#include <linux/namei.h>
+#include "internal.h"
+
+static const struct constant_table bool_names[] = {
+	{ "0",		false },
+	{ "1",		true },
+	{ "false",	false },
+	{ "no",		false },
+	{ "true",	true },
+	{ "yes",	true },
+	{ },
+};
+
+static const struct constant_table *
+__lookup_constant(const struct constant_table *tbl, const char *name)
+{
+	for ( ; tbl->name; tbl++)
+		if (strcmp(name, tbl->name) == 0)
+			return tbl;
+	return NULL;
+}
+
+/**
+ * lookup_constant - Look up a constant by name in an ordered table
+ * @tbl: The table of constants to search.
+ * @name: The name to look up.
+ * @not_found: The value to return if the name is not found.
+ */
+int lookup_constant(const struct constant_table *tbl, const char *name, int not_found)
+{
+	const struct constant_table *p = __lookup_constant(tbl, name);
+
+	return p ? p->value : not_found;
+}
+EXPORT_SYMBOL(lookup_constant);
+
+static inline bool is_flag(const struct fs_parameter_spec *p)
+{
+	return p->type == NULL;
+}
+
+static const struct fs_parameter_spec *fs_lookup_key(
+	const struct fs_parameter_spec *desc,
+	struct fs_parameter *param, bool *negated)
+{
+	const struct fs_parameter_spec *p, *other = NULL;
+	const char *name = param->key;
+	bool want_flag = param->type == fs_value_is_flag;
+
+	*negated = false;
+	for (p = desc; p->name; p++) {
+		if (strcmp(p->name, name) != 0)
+			continue;
+		if (likely(is_flag(p) == want_flag))
+			return p;
+		other = p;
+	}
+	if (want_flag) {
+		if (name[0] == 'n' && name[1] == 'o' && name[2]) {
+			for (p = desc; p->name; p++) {
+				if (strcmp(p->name, name + 2) != 0)
+					continue;
+				if (!(p->flags & fs_param_neg_with_no))
+					continue;
+				*negated = true;
+				return p;
+			}
+		}
+	}
+	return other;
+}
+
+/*
+ * __fs_parse - Parse a filesystem configuration parameter
+ * @log: The filesystem context to log errors through.
+ * @desc: The parameter description to use.
+ * @param: The parameter.
+ * @result: Where to place the result of the parse
+ *
+ * Parse a filesystem configuration parameter and attempt a conversion for a
+ * simple parameter for which this is requested.  If successful, the determined
+ * parameter ID is placed into @result->key, the desired type is indicated in
+ * @result->t and any converted value is placed into an appropriate member of
+ * the union in @result.
+ *
+ * The function returns the parameter number if the parameter was matched,
+ * -ENOPARAM if it wasn't matched and @desc->ignore_unknown indicated that
+ * unknown parameters are okay and -EINVAL if there was a conversion issue or
+ * the parameter wasn't recognised and unknowns aren't okay.
+ */
+int __fs_parse(struct p_log *log,
+	     const struct fs_parameter_spec *desc,
+	     struct fs_parameter *param,
+	     struct fs_parse_result *result)
+{
+	const struct fs_parameter_spec *p;
+
+	result->uint_64 = 0;
+
+	p = fs_lookup_key(desc, param, &result->negated);
+	if (!p)
+		return -ENOPARAM;
+
+	if (p->flags & fs_param_deprecated)
+		warn_plog(log, "Deprecated parameter '%s'", param->key);
+
+	/* Try to turn the type we were given into the type desired by the
+	 * parameter and give an error if we can't.
+	 */
+	if (is_flag(p)) {
+		if (param->type != fs_value_is_flag)
+			return inval_plog(log, "Unexpected value for '%s'",
+				      param->key);
+		result->boolean = !result->negated;
+	} else  {
+		int ret = p->type(log, p, param, result);
+		if (ret)
+			return ret;
+	}
+	return p->opt;
+}
+EXPORT_SYMBOL(__fs_parse);
+
+/**
+ * fs_lookup_param - Look up a path referred to by a parameter
+ * @fc: The filesystem context to log errors through.
+ * @param: The parameter.
+ * @want_bdev: T if want a blockdev
+ * @flags: Pathwalk flags passed to filename_lookup()
+ * @_path: The result of the lookup
+ */
+int fs_lookup_param(struct fs_context *fc,
+		    struct fs_parameter *param,
+		    bool want_bdev,
+		    unsigned int flags,
+		    struct path *_path)
+{
+	struct filename *f;
+	bool put_f;
+	int ret;
+
+	switch (param->type) {
+	case fs_value_is_string:
+		f = getname_kernel(param->string);
+		if (IS_ERR(f))
+			return PTR_ERR(f);
+		param->dirfd = AT_FDCWD;
+		put_f = true;
+		break;
+	case fs_value_is_filename:
+		f = param->name;
+		put_f = false;
+		break;
+	default:
+		return invalf(fc, "%s: not usable as path", param->key);
+	}
+
+	ret = filename_lookup(param->dirfd, f, flags, _path, NULL);
+	if (ret < 0) {
+		errorf(fc, "%s: Lookup failure for '%s'", param->key, f->name);
+		goto out;
+	}
+
+	if (want_bdev &&
+	    !S_ISBLK(d_backing_inode(_path->dentry)->i_mode)) {
+		path_put(_path);
+		_path->dentry = NULL;
+		_path->mnt = NULL;
+		errorf(fc, "%s: Non-blockdev passed as '%s'",
+		       param->key, f->name);
+		ret = -ENOTBLK;
+	}
+
+out:
+	if (put_f)
+		putname(f);
+	return ret;
+}
+EXPORT_SYMBOL(fs_lookup_param);
+
+static int fs_param_bad_value(struct p_log *log, struct fs_parameter *param)
+{
+	return inval_plog(log, "Bad value for '%s'", param->key);
+}
+
+int fs_param_is_bool(struct p_log *log, const struct fs_parameter_spec *p,
+		     struct fs_parameter *param, struct fs_parse_result *result)
+{
+	int b;
+	if (param->type != fs_value_is_string)
+		return fs_param_bad_value(log, param);
+	if (!*param->string && (p->flags & fs_param_can_be_empty))
+		return 0;
+	b = lookup_constant(bool_names, param->string, -1);
+	if (b == -1)
+		return fs_param_bad_value(log, param);
+	result->boolean = b;
+	return 0;
+}
+EXPORT_SYMBOL(fs_param_is_bool);
+
+int fs_param_is_u32(struct p_log *log, const struct fs_parameter_spec *p,
+		    struct fs_parameter *param, struct fs_parse_result *result)
+{
+	int base = (unsigned long)p->data;
+	if (param->type != fs_value_is_string)
+		return fs_param_bad_value(log, param);
+	if (!*param->string && (p->flags & fs_param_can_be_empty))
+		return 0;
+	if (kstrtouint(param->string, base, &result->uint_32) < 0)
+		return fs_param_bad_value(log, param);
+	return 0;
+}
+EXPORT_SYMBOL(fs_param_is_u32);
+
+int fs_param_is_s32(struct p_log *log, const struct fs_parameter_spec *p,
+		    struct fs_parameter *param, struct fs_parse_result *result)
+{
+	if (param->type != fs_value_is_string)
+		return fs_param_bad_value(log, param);
+	if (!*param->string && (p->flags & fs_param_can_be_empty))
+		return 0;
+	if (kstrtoint(param->string, 0, &result->int_32) < 0)
+		return fs_param_bad_value(log, param);
+	return 0;
+}
+EXPORT_SYMBOL(fs_param_is_s32);
+
+int fs_param_is_u64(struct p_log *log, const struct fs_parameter_spec *p,
+		    struct fs_parameter *param, struct fs_parse_result *result)
+{
+	if (param->type != fs_value_is_string)
+		return fs_param_bad_value(log, param);
+	if (!*param->string && (p->flags & fs_param_can_be_empty))
+		return 0;
+	if (kstrtoull(param->string, 0, &result->uint_64) < 0)
+		return fs_param_bad_value(log, param);
+	return 0;
+}
+EXPORT_SYMBOL(fs_param_is_u64);
+
+int fs_param_is_enum(struct p_log *log, const struct fs_parameter_spec *p,
+		     struct fs_parameter *param, struct fs_parse_result *result)
+{
+	const struct constant_table *c;
+	if (param->type != fs_value_is_string)
+		return fs_param_bad_value(log, param);
+	if (!*param->string && (p->flags & fs_param_can_be_empty))
+		return 0;
+	c = __lookup_constant(p->data, param->string);
+	if (!c)
+		return fs_param_bad_value(log, param);
+	result->uint_32 = c->value;
+	return 0;
+}
+EXPORT_SYMBOL(fs_param_is_enum);
+
+int fs_param_is_string(struct p_log *log, const struct fs_parameter_spec *p,
+		       struct fs_parameter *param, struct fs_parse_result *result)
+{
+	if (param->type != fs_value_is_string ||
+	    (!*param->string && !(p->flags & fs_param_can_be_empty)))
+		return fs_param_bad_value(log, param);
+	return 0;
+}
+EXPORT_SYMBOL(fs_param_is_string);
+
+int fs_param_is_fd(struct p_log *log, const struct fs_parameter_spec *p,
+		  struct fs_parameter *param, struct fs_parse_result *result)
+{
+	switch (param->type) {
+	case fs_value_is_string:
+		if ((!*param->string && !(p->flags & fs_param_can_be_empty)) ||
+		    kstrtouint(param->string, 0, &result->uint_32) < 0)
+			break;
+		if (result->uint_32 <= INT_MAX)
+			return 0;
+		break;
+	case fs_value_is_file:
+		result->uint_32 = param->dirfd;
+		if (result->uint_32 <= INT_MAX)
+			return 0;
+		break;
+	default:
+		break;
+	}
+	return fs_param_bad_value(log, param);
+}
+EXPORT_SYMBOL(fs_param_is_fd);
+
+int fs_param_is_file_or_string(struct p_log *log,
+			       const struct fs_parameter_spec *p,
+			       struct fs_parameter *param,
+			       struct fs_parse_result *result)
+{
+	switch (param->type) {
+	case fs_value_is_string:
+		return fs_param_is_string(log, p, param, result);
+	case fs_value_is_file:
+		result->uint_32 = param->dirfd;
+		if (result->uint_32 <= INT_MAX)
+			return 0;
+		break;
+	default:
+		break;
+	}
+	return fs_param_bad_value(log, param);
+}
+EXPORT_SYMBOL(fs_param_is_file_or_string);
+
+int fs_param_is_uid(struct p_log *log, const struct fs_parameter_spec *p,
+		    struct fs_parameter *param, struct fs_parse_result *result)
+{
+	kuid_t uid;
+
+	if (fs_param_is_u32(log, p, param, result) != 0)
+		return fs_param_bad_value(log, param);
+
+	uid = make_kuid(current_user_ns(), result->uint_32);
+	if (!uid_valid(uid))
+		return inval_plog(log, "Invalid uid '%s'", param->string);
+
+	result->uid = uid;
+	return 0;
+}
+EXPORT_SYMBOL(fs_param_is_uid);
+
+int fs_param_is_gid(struct p_log *log, const struct fs_parameter_spec *p,
+		    struct fs_parameter *param, struct fs_parse_result *result)
+{
+	kgid_t gid;
+
+	if (fs_param_is_u32(log, p, param, result) != 0)
+		return fs_param_bad_value(log, param);
+
+	gid = make_kgid(current_user_ns(), result->uint_32);
+	if (!gid_valid(gid))
+		return inval_plog(log, "Invalid gid '%s'", param->string);
+
+	result->gid = gid;
+	return 0;
+}
+EXPORT_SYMBOL(fs_param_is_gid);
+
+int fs_param_is_blockdev(struct p_log *log, const struct fs_parameter_spec *p,
+		  struct fs_parameter *param, struct fs_parse_result *result)
+{
+	return 0;
+}
+EXPORT_SYMBOL(fs_param_is_blockdev);
+
+#ifdef CONFIG_VALIDATE_FS_PARSER
+/**
+ * fs_validate_description - Validate a parameter specification array
+ * @name: Owner name of the parameter specification array
+ * @desc: The parameter specification array to validate.
+ */
+bool fs_validate_description(const char *name,
+	const struct fs_parameter_spec *desc)
+{
+	const struct fs_parameter_spec *param, *p2;
+	bool good = true;
+
+	for (param = desc; param->name; param++) {
+		/* Check for duplicate parameter names */
+		for (p2 = desc; p2 < param; p2++) {
+			if (strcmp(param->name, p2->name) == 0) {
+				if (is_flag(param) != is_flag(p2))
+					continue;
+				pr_err("VALIDATE %s: PARAM[%s]: Duplicate\n",
+				       name, param->name);
+				good = false;
+			}
+		}
+	}
+	return good;
+}
+#endif /* CONFIG_VALIDATE_FS_PARSER */