There is a possible race between removing a cgroup diectory that is a partition root and the creation of a new partition. The partition to be removed can be dying but still online, it doesn't not currently participate in checking for exclusive CPUs conflict, but the exclusive CPUs are still there in subpartitions_cpus and isolated_cpus. These two cpumasks are global states that affect the operation of cpuset partitions. The exclusive CPUs in dying cpusets will only be removed when cpuset_css_offline() function is called after an RCU delay.
As a result, it is possible that a new partition can be created with exclusive CPUs that overlap with those of a dying one. When that dying partition is finally offlined, it removes those overlapping exclusive CPUs from subpartitions_cpus and maybe isolated_cpus resulting in an incorrect CPU configuration.
This bug was found when a warning was triggered in remote_partition_disable() during testing because the subpartitions_cpus mask was empty.
One possible way to fix this is to iterate the dying cpusets as well and avoid using the exclusive CPUs in those dying cpusets. However, this can still cause random partition creation failures or other anomalies due to racing. A better way to fix this race is to reset the partition state at the moment when a cpuset is being killed.
Introduce a new css_killed() CSS function pointer and call it, if defined, before setting CSS_DYING flag in kill_css(). Also update the css_is_dying() helper to use the CSS_DYING flag introduced by commit 33c35aa48178 ("cgroup: Prevent kill_css() from being called more than once") for proper synchronization.
Add a new cpuset_css_killed() function to reset the partition state of a valid partition root if it is being killed.
Fixes: ee8dde0cd2ce ("cpuset: Add new v2 cpuset.sched.partition flag") Signed-off-by: Waiman Long longman@redhat.com --- include/linux/cgroup-defs.h | 1 + include/linux/cgroup.h | 2 +- kernel/cgroup/cgroup.c | 6 ++++++ kernel/cgroup/cpuset.c | 20 +++++++++++++++++--- 4 files changed, 25 insertions(+), 4 deletions(-)
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h index 485b651869d9..5bc8f55c8cca 100644 --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -710,6 +710,7 @@ struct cgroup_subsys { void (*css_released)(struct cgroup_subsys_state *css); void (*css_free)(struct cgroup_subsys_state *css); void (*css_reset)(struct cgroup_subsys_state *css); + void (*css_killed)(struct cgroup_subsys_state *css); void (*css_rstat_flush)(struct cgroup_subsys_state *css, int cpu); int (*css_extra_stat_show)(struct seq_file *seq, struct cgroup_subsys_state *css); diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index 28e999f2c642..e7da3c3b098b 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -344,7 +344,7 @@ static inline u64 cgroup_id(const struct cgroup *cgrp) */ static inline bool css_is_dying(struct cgroup_subsys_state *css) { - return !(css->flags & CSS_NO_REF) && percpu_ref_is_dying(&css->refcnt); + return css->flags & CSS_DYING; }
static inline void cgroup_get(struct cgroup *cgrp) diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index f231fe3a0744..49d622205997 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -5909,6 +5909,12 @@ static void kill_css(struct cgroup_subsys_state *css) if (css->flags & CSS_DYING) return;
+ /* + * Call css_killed(), if defined, before setting the CSS_DYING flag + */ + if (css->ss->css_killed) + css->ss->css_killed(css); + css->flags |= CSS_DYING;
/* diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 39c1fc643d77..749994312d47 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -3475,9 +3475,6 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css) cpus_read_lock(); mutex_lock(&cpuset_mutex);
- if (is_partition_valid(cs)) - update_prstate(cs, 0); - if (!cpuset_v2() && is_sched_load_balance(cs)) cpuset_update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);
@@ -3488,6 +3485,22 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css) cpus_read_unlock(); }
+static void cpuset_css_killed(struct cgroup_subsys_state *css) +{ + struct cpuset *cs = css_cs(css); + + cpus_read_lock(); + mutex_lock(&cpuset_mutex); + + /* Reset valid partition back to member */ + if (is_partition_valid(cs)) + update_prstate(cs, PRS_MEMBER); + + mutex_unlock(&cpuset_mutex); + cpus_read_unlock(); + +} + static void cpuset_css_free(struct cgroup_subsys_state *css) { struct cpuset *cs = css_cs(css); @@ -3609,6 +3622,7 @@ struct cgroup_subsys cpuset_cgrp_subsys = { .css_alloc = cpuset_css_alloc, .css_online = cpuset_css_online, .css_offline = cpuset_css_offline, + .css_killed = cpuset_css_killed, .css_free = cpuset_css_free, .can_attach = cpuset_can_attach, .cancel_attach = cpuset_cancel_attach,