cgroup: CGRP_ROOT_SUBSYS_BOUND should be ignored when comparing mount options (0ce6cba3) · Commits · 戴 / test

("cgroup: fix cgroupfs_root early destruction path") introduced CGRP_ROOT_SUBSYS_BOUND which is used to mark completion of subsys binding on a new root; however, this broke remounts. cgroup_remount() doesn't allow changing root options via remount and CGRP_ROOT_SUBSYS_BOUND, which is set on all fully initialized roots, makes the function reject all remounts. Fix it by putting the options part in the lower 16 bits of root->flags and masking the comparions. While at it, make cgroup_remount() emit an error message explaining why it's rejecting a remount request, so that it's less of a mystery. Signed-off-by:

Tejun Heo <tj@kernel.org>

include/linux/cgroup.h

+5 −1

Original line number	Diff line number	Diff line
		@@ -276,7 +276,11 @@ enum {

		CGRP_ROOT_NOPREFIX = (1 << 1), /* mounted subsystems have no named prefix */
		CGRP_ROOT_XATTR = (1 << 2), /* supports extended attributes */
		CGRP_ROOT_SUBSYS_BOUND = (1 << 3), /* subsystems finished binding */

		/* mount options live below bit 16 */
		CGRP_ROOT_OPTION_MASK = (1 << 16) - 1,

		CGRP_ROOT_SUBSYS_BOUND = (1 << 16), /* subsystems finished binding */
		};

		/*

kernel/cgroup.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -1362,8 +1362,11 @@ static int cgroup_remount(struct super_block sb, int flags, char *data)
		removed_mask = root->subsys_mask & ~opts.subsys_mask;

		/* Don't allow flags or name to change at remount */
		if (opts.flags != root->flags \|\|
		if (((opts.flags ^ root->flags) & CGRP_ROOT_OPTION_MASK) \|\|
		(opts.name && strcmp(opts.name, root->name))) {
		pr_err("cgroup: option or name mismatch, new: 0x%lx \"%s\", old: 0x%lx \"%s\"\n",
		opts.flags & CGRP_ROOT_OPTION_MASK, opts.name ?: "",
		root->flags & CGRP_ROOT_OPTION_MASK, root->name);
		ret = -EINVAL;
		goto out_unlock;
		}

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