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Commit 4ac06017 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: release cgroup_mutex over file removals 



Now that cftypes and all tree modification operations are protected by
cgroup_tree_mutex, we can drop cgroup_mutex while deleting files and
directories.  Drop cgroup_mutex over removals.

This doesn't make any noticeable difference now but is to help kernfs
conversion.  In kernfs, removals are sync points which drain in-flight
operations as those operations would grab cgroup_mutex, trying to
delete under cgroup_mutex would deadlock.  This can be resolved by
just holding the outer cgroup_tree_mutex which nests outside both
kernfs active reference and cgroup_mutex.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent ace2bee8

kernel/cgroup.c

+10 −5
Original line number Diff line number Diff line
@@ -976,7 +976,9 @@ static int rebind_subsystems(struct cgroupfs_root *root, 
	 * Nothing can fail from this point on.  Remove files for the

	 * removed subsystems and rebind each subsystem.

	 */

	mutex_unlock(&cgroup_mutex);

	cgroup_clear_dir(cgrp, removed_mask);

	mutex_lock(&cgroup_mutex);



	for_each_subsys(ss, i) {

		unsigned long bit = 1UL << i;
@@ -2696,10 +2698,11 @@ static int cgroup_cfts_commit(struct cftype *cfts, bool is_add) 
	u64 update_before;

	int ret = 0;



	mutex_unlock(&cgroup_mutex);



	/* %NULL @cfts indicates abort and don't bother if @ss isn't attached */

	if (!cfts || ss->root == &cgroup_dummy_root ||

	    !atomic_inc_not_zero(&sb->s_active)) {

		mutex_unlock(&cgroup_mutex);

		mutex_unlock(&cgroup_tree_mutex);

		return 0;

	}
@@ -2723,18 +2726,15 @@ static int cgroup_cfts_commit(struct cftype *cfts, bool is_add) 
		dput(prev);

		prev = cgrp->dentry;



		mutex_unlock(&cgroup_mutex);

		mutex_unlock(&cgroup_tree_mutex);

		mutex_lock(&inode->i_mutex);

		mutex_lock(&cgroup_tree_mutex);

		mutex_lock(&cgroup_mutex);

		if (cgrp->serial_nr < update_before && !cgroup_is_dead(cgrp))

			ret = cgroup_addrm_files(cgrp, cfts, is_add);

		mutex_unlock(&inode->i_mutex);

		if (ret)

			break;

	}

	mutex_unlock(&cgroup_mutex);

	mutex_unlock(&cgroup_tree_mutex);

	dput(prev);

	deactivate_super(sb);
@@ -4387,10 +4387,13 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) 
	/*

	 * Initiate massacre of all css's.  cgroup_destroy_css_killed()

	 * will be invoked to perform the rest of destruction once the

	 * percpu refs of all css's are confirmed to be killed.

	 * percpu refs of all css's are confirmed to be killed.  This

	 * involves removing the subsystem's files, drop cgroup_mutex.

	 */

	mutex_unlock(&cgroup_mutex);

	for_each_css(css, ssid, cgrp)

		kill_css(css);

	mutex_lock(&cgroup_mutex);



	/*

	 * Mark @cgrp dead.  This prevents further task migration and child
@@ -4421,9 +4424,11 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) 
	 * puts the base ref but we aren't quite done with @cgrp yet, so

	 * hold onto it.

	 */

	mutex_unlock(&cgroup_mutex);

	cgroup_addrm_files(cgrp, cgroup_base_files, false);

	dget(d);

	cgroup_d_remove_dir(d);

	mutex_lock(&cgroup_mutex);



	return 0;

};