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author | 2019-01-12 00:20:54 -0500 | |
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committer | 2019-01-17 11:53:02 -0500 | |
commit | 35ac1184244f1329783e1d897f74926d8bb1103a (patch) | |
tree | 948885626366907d39c1d4540a89283ed2fb1a01 /kernel/cgroup/cgroup.c | |
parent | fix cgroup_do_mount() handling of failure exits (diff) | |
download | linux-35ac1184244f1329783e1d897f74926d8bb1103a.tar.gz linux-35ac1184244f1329783e1d897f74926d8bb1103a.tar.bz2 linux-35ac1184244f1329783e1d897f74926d8bb1103a.zip |
cgroup: saner refcounting for cgroup_root
* make the reference from superblock to cgroup_root counting -
do cgroup_put() in cgroup_kill_sb() whether we'd done
percpu_ref_kill() or not; matching grab is done when we allocate
a new root. That gives the same refcounting rules for all callers
of cgroup_do_mount() - a reference to cgroup_root has been grabbed
by caller and it either is transferred to new superblock or dropped.
* have cgroup_kill_sb() treat an already killed refcount as "just
don't bother killing it, then".
* after successful cgroup_do_mount() have cgroup1_mount() recheck
if we'd raced with mount/umount from somebody else and cgroup_root
got killed. In that case we drop the superblock and bugger off
with -ERESTARTSYS, same as if we'd found it in the list already
dying.
* don't bother with delayed initialization of refcount - it's
unreliable and not needed. No need to prevent attempts to bump
the refcount if we find cgroup_root of another mount in progress -
sget will reuse an existing superblock just fine and if the
other sb manages to die before we get there, we'll catch
that immediately after cgroup_do_mount().
* don't bother with kernfs_pin_sb() - no need for doing that
either.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'kernel/cgroup/cgroup.c')
-rw-r--r-- | kernel/cgroup/cgroup.c | 16 |
1 files changed, 7 insertions, 9 deletions
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 503bba3c4bae..7fd9f22e406d 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -1927,7 +1927,7 @@ void init_cgroup_root(struct cgroup_root *root, struct cgroup_sb_opts *opts) set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags); } -int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask, int ref_flags) +int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask) { LIST_HEAD(tmp_links); struct cgroup *root_cgrp = &root->cgrp; @@ -1944,7 +1944,7 @@ int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask, int ref_flags) root_cgrp->ancestor_ids[0] = ret; ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release, - ref_flags, GFP_KERNEL); + 0, GFP_KERNEL); if (ret) goto out; @@ -2121,18 +2121,16 @@ static void cgroup_kill_sb(struct super_block *sb) struct cgroup_root *root = cgroup_root_from_kf(kf_root); /* - * If @root doesn't have any mounts or children, start killing it. + * If @root doesn't have any children, start killing it. * This prevents new mounts by disabling percpu_ref_tryget_live(). * cgroup_mount() may wait for @root's release. * * And don't kill the default root. */ - if (!list_empty(&root->cgrp.self.children) || - root == &cgrp_dfl_root) - cgroup_put(&root->cgrp); - else + if (list_empty(&root->cgrp.self.children) && root != &cgrp_dfl_root && + !percpu_ref_is_dying(&root->cgrp.self.refcnt)) percpu_ref_kill(&root->cgrp.self.refcnt); - + cgroup_put(&root->cgrp); kernfs_kill_sb(sb); } @@ -5402,7 +5400,7 @@ int __init cgroup_init(void) hash_add(css_set_table, &init_css_set.hlist, css_set_hash(init_css_set.subsys)); - BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0, 0)); + BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0)); mutex_unlock(&cgroup_mutex); |