hulk inclusion category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I99KM6

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When read/write memory.wb_blkio_ino of a memcg, and delete the memcg at the same time, it could cause deadlock as below: CPU0 CPU1 rlock(kn->active#4); lock(cgroup_mutex); lock(kn->active#4); lock(cgroup_mutex);

Therefore, use cgroup_kn_lock_live to replace cgroup_mutex in reading/writing memory.wb_blkio_ino. cgroup_kn_lock_live is locking helper for cgroup kernfs methods.

Fixes: cf4973d8f67c ("cgroup: support cgroup writeback on cgroupv1") Signed-off-by: Chen Ridong chenridong@huawei.com --- mm/backing-dev.c | 5 +++-- mm/memcontrol.c | 13 ++++++++----- 2 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c index d70f8420c805..a62efda13ee8 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -579,8 +579,8 @@ static struct cgroup_subsys_state *cgwbv1_get_blkcss(struct mem_cgroup *memcg) struct cgroup_subsys_state *blkcg_css;

rcu_read_lock(); - blkcg_css = memcg->wb_blk_css; - if (!css_tryget_online(blkcg_css)) { + blkcg_css = READ_ONCE(memcg->wb_blk_css); + if (!blkcg_css || !css_tryget_online(blkcg_css)) { blkcg_css = blkcg_root_css; css_get(blkcg_css); } @@ -1180,6 +1180,7 @@ static void wb_kill_memcg(struct cgroup_subsys_state *memcg_css)

list_del_init(&memcg->memcg_node); css_put(memcg->wb_blk_css); + memcg->wb_blk_css = NULL; }

static void wb_kill_blkcg(struct cgroup_subsys_state *blkcg_css) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 0f1813deb527..df2d73ad85cf 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -6029,6 +6029,7 @@ static ssize_t memcg_high_async_ratio_write(struct kernfs_open_file *of,

static int wb_blkio_show(struct seq_file *m, void *v) { + struct kernfs_open_file *of = m->private; char *path; ino_t blkcg_id; struct cgroup *blkcg_cgroup; @@ -6042,12 +6043,13 @@ static int wb_blkio_show(struct seq_file *m, void *v) if (!path) return -ENOMEM;

- mutex_lock(&cgroup_mutex); + if (!cgroup_kn_lock_live(of->kn, false)) + return -ENODEV; blkcg_css = memcg->wb_blk_css; blkcg_cgroup = blkcg_css->cgroup; blkcg_id = cgroup_ino(blkcg_cgroup); cgroup_path(blkcg_cgroup, path, PATH_MAX); - mutex_unlock(&cgroup_mutex); + cgroup_kn_unlock(of->kn); seq_printf(m, "wb_blkio_path:%s\n", path); seq_printf(m, "wb_blkio_ino:%lu\n", blkcg_id); kfree(path); @@ -6073,11 +6075,12 @@ static ssize_t wb_blkio_write(struct kernfs_open_file *of, char *buf, if (ret) return ret;

- mutex_lock(&cgroup_mutex); + if (!cgroup_kn_lock_live(of->kn, false)) + return -ENODEV; root = blkcg_root_css->cgroup->root; blk_cgroup = __cgroup_get_from_id(root, cgrp_id); if (IS_ERR(blk_cgroup)) { - mutex_unlock(&cgroup_mutex); + cgroup_kn_unlock(of->kn); return -EINVAL; } blkcg_css = cgroup_tryget_css(blk_cgroup, &io_cgrp_subsys); @@ -6088,7 +6091,7 @@ static ssize_t wb_blkio_write(struct kernfs_open_file *of, char *buf,

out_unlock: cgroup_put(blk_cgroup); - mutex_unlock(&cgroup_mutex); + cgroup_kn_unlock(of->kn);

return ret < 0 ? ret : nbytes; }