Messages in this thread Patch in this message | | | Subject | [PATCH 2/2] sched/core: fix cpu_hotplug_lock recursion in tg_set_cfs_bandwidth() | From | Konstantin Khlebnikov <> | Date | Wed, 03 Jan 2018 23:29:57 +0300 |
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After commit fc8dffd379ca ("cpu/hotplug: Convert hotplug locking to percpu rwsem") get_online_cpus() must be non-recursive.
Cpu hotplug is already locked for read in tg_set_cfs_bandwidth() and static_key_slow_inc() in cfs_bandwidth_usage_inc() locks it again.
Switch to cpus_read_[un]lock() and static_key_slow_inc/dec_cpuslocked().
This fixes lockdep warning:
============================================ WARNING: possible recursive locking detected 4.14.11-debug-test #5 Not tainted -------------------------------------------- portod-worker27/4773 is trying to acquire lock: (cpu_hotplug_lock.rw_sem){++++}, at: static_key_slow_inc+0xe/0x170
but task is already holding lock: (cpu_hotplug_lock.rw_sem){++++}, at: tg_set_cfs_bandwidth+0xc6/0x890
other info that might help us debug this: Possible unsafe locking scenario:
CPU0 ---- lock(cpu_hotplug_lock.rw_sem); lock(cpu_hotplug_lock.rw_sem);
*** DEADLOCK ***
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> --- kernel/sched/core.c | 4 ++-- kernel/sched/fair.c | 4 ++-- kernel/sched/sched.h | 1 + 3 files changed, 5 insertions(+), 4 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 644fa2e3d993..584832b49fdc 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6448,7 +6448,7 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota) * Prevent race between setting of cfs_rq->runtime_enabled and * unthrottle_offline_cfs_rqs(). */ - get_online_cpus(); + cpus_read_lock(); mutex_lock(&cfs_constraints_mutex); ret = __cfs_schedulable(tg, period, quota); if (ret) @@ -6491,7 +6491,7 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota) cfs_bandwidth_usage_dec(); out_unlock: mutex_unlock(&cfs_constraints_mutex); - put_online_cpus(); + cpus_read_unlock(); return ret; } diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 2fe3aa853e4d..26a71ebcd3c2 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4365,12 +4365,12 @@ static inline bool cfs_bandwidth_used(void) void cfs_bandwidth_usage_inc(void) { - static_key_slow_inc(&__cfs_bandwidth_used); + static_key_slow_inc_cpuslocked(&__cfs_bandwidth_used); } void cfs_bandwidth_usage_dec(void) { - static_key_slow_dec(&__cfs_bandwidth_used); + static_key_slow_dec_cpuslocked(&__cfs_bandwidth_used); } #else /* HAVE_JUMP_LABEL */ static bool cfs_bandwidth_used(void) diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index b19552a212de..7dddc531ba63 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2007,6 +2007,7 @@ extern void init_cfs_rq(struct cfs_rq *cfs_rq); extern void init_rt_rq(struct rt_rq *rt_rq); extern void init_dl_rq(struct dl_rq *dl_rq); +/* Must be called under cpus_read_lock() */ extern void cfs_bandwidth_usage_inc(void); extern void cfs_bandwidth_usage_dec(void);
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