Re: [PATCH -next] memcg: fix sleep in invalid context in cgroup_rstat_flush()
From: Shakeel Butt <hidden>
Date: 2021-07-16 12:43:27
Also in:
linux-mm, lkml
On Fri, Jul 16, 2021 at 1:45 AM Yang Yingliang [off-list ref] 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 <redacted>Thanks for the report.
quoted hunk ↗ jump to hunk
--- 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.
quoted hunk ↗ jump to hunk
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