On Fri, Jul 16, 2021 at 1:45 AM Yang Yingliang <yangyingliang@xxxxxxxxxx> wrote:
>
> When start the kernel, I got this report:
>
> [ 13.787531][ T248] BUG: sleeping function called from invalid context at kernel/cgroup/rstat.c:200
> [ 13.788799][ T248] in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 248, name: kworker/u8:3
> [ 13.789971][ T248] 3 locks held by kworker/u8:3/248:
> [ 13.790638][ T248] #0: ffff888100100138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work+0x942/0x17d0
> [ 13.792170][ T248] #1: ffffc900018bfe00 (stats_flush_work){+.+.}-{0:0}, at: process_one_work+0x977/0x17d0
> [ 13.793477][ T248] #2: ffffffff8baccf78 (stats_flush_lock){+.+.}-{2:2}, at: mem_cgroup_flush_stats+0xd/0x50
> [ 13.794815][ T248] Preemption disabled at:
> [ 13.794821][ T248] [<0000000000000000>] 0x0
> [ 13.795951][ T248] CPU: 2 PID: 248 Comm: kworker/u8:3 Tainted: G W 5.14.0-rc1-next-20210716+ #342
> [ 13.797287][ T248] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
> [ 13.798564][ T248] Workqueue: events_unbound flush_memcg_stats_work
> [ 13.799400][ T248] Call Trace:
> [ 13.799817][ T248] dump_stack_lvl+0xcd/0x134
> [ 13.800405][ T248] ___might_sleep.cold.155+0x1f2/0x238
> [ 13.801107][ T248] cgroup_rstat_flush+0x1c/0x50
> [ 13.801724][ T248] mem_cgroup_flush_stats+0x39/0x50
> [ 13.802131][ T248] process_one_work+0xa6c/0x17d0
> [ 13.802131][ T248] ? pwq_dec_nr_in_flight+0x360/0x360
> [ 13.802131][ T248] ? do_raw_spin_lock+0x121/0x2d0
> [ 13.802131][ T248] worker_thread+0x8c/0xda0
> [ 13.802131][ T248] ? process_one_work+0x17d0/0x17d0
> [ 13.802131][ T248] kthread+0x3d5/0x4c0
> [ 13.802131][ T248] ? set_kthread_struct+0x130/0x130
> [ 13.802131][ T248] ret_from_fork+0x1f/0x30
>
> To fix this, move stats_flush_lock into cgroup_rstat_flush() after might_sleep(),
> unlock stats_flush_lock before sleep in cgroup_rstat_flush_locked() and lock
> stats_flush_lock after wake up.
>
> Fixes: 42265e014ac7 ("memcg: infrastructure to flush memcg stats")
> Signed-off-by: Yang Yingliang <yangyingliang@xxxxxxxxxx>
Thanks for the report.
> ---
> kernel/cgroup/rstat.c | 7 +++++++
> mm/memcontrol.c | 5 -----
> 2 files changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
> index 7f0e58917432..d7ce96ba0105 100644
> --- a/kernel/cgroup/rstat.c
> +++ b/kernel/cgroup/rstat.c
> @@ -5,6 +5,7 @@
>
> static DEFINE_SPINLOCK(cgroup_rstat_lock);
> static DEFINE_PER_CPU(raw_spinlock_t, cgroup_rstat_cpu_lock);
> +static DEFINE_SPINLOCK(stats_flush_lock);
>
> static void cgroup_base_stat_flush(struct cgroup *cgrp, int cpu);
>
> @@ -175,8 +176,10 @@ static void cgroup_rstat_flush_locked(struct cgroup *cgrp, bool may_sleep)
> if (may_sleep && (need_resched() ||
> spin_needbreak(&cgroup_rstat_lock))) {
> spin_unlock_irq(&cgroup_rstat_lock);
> + spin_unlock(&stats_flush_lock);
> if (!cond_resched())
> cpu_relax();
> + spin_lock(&stats_flush_lock);
> spin_lock_irq(&cgroup_rstat_lock);
> }
> }
> @@ -199,9 +202,13 @@ void cgroup_rstat_flush(struct cgroup *cgrp)
> {
> might_sleep();
>
> + if (!spin_trylock(&stats_flush_lock))
> + return;
> +
No, there is no point of stats_flush_lock if we add this to rstat and
take it for everyone.
> spin_lock_irq(&cgroup_rstat_lock);
> cgroup_rstat_flush_locked(cgrp, true);
> spin_unlock_irq(&cgroup_rstat_lock);
> + spin_unlock(&stats_flush_lock);
> }
>
> /**
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 456f5310ea59..c6b0f5b41893 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -109,7 +109,6 @@ static DECLARE_DEFERRABLE_WORK(stats_flush_dwork, flush_memcg_stats_dwork);
> static void flush_memcg_stats_work(struct work_struct *w);
> static DECLARE_WORK(stats_flush_work, flush_memcg_stats_work);
> static DEFINE_PER_CPU(unsigned int, stats_flush_threshold);
> -static DEFINE_SPINLOCK(stats_flush_lock);
>
> #define THRESHOLDS_EVENTS_TARGET 128
> #define SOFTLIMIT_EVENTS_TARGET 1024
> @@ -5355,11 +5354,7 @@ static void mem_cgroup_css_reset(struct cgroup_subsys_state *css)
>
> void mem_cgroup_flush_stats(void)
> {
> - if (!spin_trylock(&stats_flush_lock))
> - return;
> -
> cgroup_rstat_flush(root_mem_cgroup->css.cgroup);
We should change this to cgroup_rstat_flush_irqsafe(). One addition we
can do is to change all rstat flush callsites in memcontrol.c to go
through mem_cgroup_flush_stats()
> - spin_unlock(&stats_flush_lock);
> }
>
> static void flush_memcg_stats_dwork(struct work_struct *w)
> --
> 2.25.1
>
