From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roman Gushchin Subject: [PATCH v3 3/7] cgroup: protect cgroup->nr_(dying_)descendants by css_set_lock Date: Fri, 16 Nov 2018 16:38:26 -0800 Message-ID: <20181117003830.15344-4-guro@fb.com> References: <20181117003830.15344-1-guro@fb.com> Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=g+x0Z8u1o4aOWMcidhd9IWCml4xwrNc4H7EaMb8VtdA=; b=Ru0kcIM4utPcHoBGfTYmpaShtLyReVfIpaLr6Zj+WPIlxZKnKd7zIQiCVjzDexKfgs IzhMurfmNkQAWAy7yZn4zAr2xbuF0CdESDr2V1/entgxH7URYTOJ3O2oguyhuIYGgJP1 wQsyPuEBilOFqZTCVTchgjtalPoEMIl8hhKIPJt1nGGdiKWInZiXslus0fg9OhEpBPik oXdBX+2kIXfAFhbn1bLeBm7EV5FaMttE1d5Bdjykz+sfbSGuCSSium5m1hkEg0gPBpaA lSMTqkmxYCv2Ma0YV/5Ix1lhSZxrpvYWfS0UMPdzDdCbk+kT2clNnMlzwR7VYHShF1lS E67A== In-Reply-To: <20181117003830.15344-1-guro@fb.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Tejun Heo Cc: Oleg Nesterov , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, Roman Gushchin Now the number of descendant cgroups and the number of dying descendant cgroups are synchronized using the cgroup_mutex. The number of descendant cgroups will be required by the cgroup v2 freezer, which will use it to determine if a cgroup is frozen (depending on total number of descendants and number of frozen descendants). It's not always acceptable to grab the cgroup_mutex, especially from quite hot paths (e.g. exit()). To avoid this, let's additionally synchronize these counters using the css_set_lock. Signed-off-by: Roman Gushchin Cc: Tejun Heo Cc: kernel-team@fb.com --- include/linux/cgroup-defs.h | 3 +++ kernel/cgroup/cgroup.c | 20 ++++++++++++++++---- 2 files changed, 19 insertions(+), 4 deletions(-) diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h index 22254c1fe1c5..9e77559c7f49 100644 --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -346,6 +346,9 @@ struct cgroup { * Dying cgroups are cgroups which were deleted by a user, * but are still existing because someone else is holding a reference. * max_descendants is a maximum allowed number of descent cgroups. + * + * nr_descendants and nr_dying_descendants are protected + * by css_set_lock. */ int nr_descendants; int nr_dying_descendants; diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index ef3442555b32..2241cb1d1238 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -3409,11 +3409,15 @@ static int cgroup_events_show(struct seq_file *seq, void *v) static int cgroup_stat_show(struct seq_file *seq, void *v) { struct cgroup *cgroup = seq_css(seq)->cgroup; + int nr_descendants, nr_dying_descendants; - seq_printf(seq, "nr_descendants %d\n", - cgroup->nr_descendants); - seq_printf(seq, "nr_dying_descendants %d\n", - cgroup->nr_dying_descendants); + spin_lock_irq(&css_set_lock); + nr_descendants = cgroup->nr_descendants; + nr_dying_descendants = cgroup->nr_dying_descendants; + spin_unlock_irq(&css_set_lock); + + seq_printf(seq, "nr_descendants %d\n", nr_descendants); + seq_printf(seq, "nr_dying_descendants %d\n", nr_dying_descendants); return 0; } @@ -4684,9 +4688,11 @@ static void css_release_work_fn(struct work_struct *work) if (cgroup_on_dfl(cgrp)) cgroup_rstat_flush(cgrp); + spin_lock_irq(&css_set_lock); for (tcgrp = cgroup_parent(cgrp); tcgrp; tcgrp = cgroup_parent(tcgrp)) tcgrp->nr_dying_descendants--; + spin_unlock_irq(&css_set_lock); cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id); cgrp->id = -1; @@ -4899,12 +4905,14 @@ static struct cgroup *cgroup_create(struct cgroup *parent) if (ret) goto out_idr_free; + spin_lock_irq(&css_set_lock); for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp)) { cgrp->ancestor_ids[tcgrp->level] = tcgrp->id; if (tcgrp != cgrp) tcgrp->nr_descendants++; } + spin_unlock_irq(&css_set_lock); if (notify_on_release(parent)) set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags); @@ -4956,6 +4964,7 @@ static bool cgroup_check_hierarchy_limits(struct cgroup *parent) lockdep_assert_held(&cgroup_mutex); + spin_lock_irq(&css_set_lock); for (cgroup = parent; cgroup; cgroup = cgroup_parent(cgroup)) { if (cgroup->nr_descendants >= cgroup->max_descendants) goto fail; @@ -4968,6 +4977,7 @@ static bool cgroup_check_hierarchy_limits(struct cgroup *parent) ret = true; fail: + spin_unlock_irq(&css_set_lock); return ret; } @@ -5187,10 +5197,12 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) if (parent && cgroup_is_threaded(cgrp)) parent->nr_threaded_children--; + spin_lock_irq(&css_set_lock); for (tcgrp = cgroup_parent(cgrp); tcgrp; tcgrp = cgroup_parent(tcgrp)) { tcgrp->nr_descendants--; tcgrp->nr_dying_descendants++; } + spin_unlock_irq(&css_set_lock); cgroup1_check_for_release(parent); -- 2.17.2