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Message-Id: <20230206130449.41360-1-wander@redhat.com>
Date: Mon, 6 Feb 2023 10:04:47 -0300
From: Wander Lairson Costa <wander@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Andy Lutomirski <luto@...nel.org>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>,
Fenghua Yu <fenghua.yu@...el.com>,
Wander Lairson Costa <wander@...hat.com>,
Andrei Vagin <avagin@...il.com>,
linux-kernel@...r.kernel.org (open list)
Cc: Hu Chunyu <chuhu@...hat.com>, Oleg Nesterov <oleg@...hat.com>,
Valentin Schneider <vschneid@...hat.com>,
Paul McKenney <paulmck@...nel.org>
Subject: [PATCH v4] kernel/fork: beware of __put_task_struct calling context
Under PREEMPT_RT, __put_task_struct() indirectly acquires sleeping
locks. Therefore, it can't be called from an non-preemptible context.
One practical example is splat inside inactive_task_timer(), which is
called in a interrupt context:
CPU: 1 PID: 2848 Comm: life Kdump: loaded Tainted: G W ---------
Hardware name: HP ProLiant DL388p Gen8, BIOS P70 07/15/2012
Call Trace:
dump_stack_lvl+0x57/0x7d
mark_lock_irq.cold+0x33/0xba
? stack_trace_save+0x4b/0x70
? save_trace+0x55/0x150
mark_lock+0x1e7/0x400
mark_usage+0x11d/0x140
__lock_acquire+0x30d/0x930
lock_acquire.part.0+0x9c/0x210
? refill_obj_stock+0x3d/0x3a0
? rcu_read_lock_sched_held+0x3f/0x70
? trace_lock_acquire+0x38/0x140
? lock_acquire+0x30/0x80
? refill_obj_stock+0x3d/0x3a0
rt_spin_lock+0x27/0xe0
? refill_obj_stock+0x3d/0x3a0
refill_obj_stock+0x3d/0x3a0
? inactive_task_timer+0x1ad/0x340
kmem_cache_free+0x357/0x560
inactive_task_timer+0x1ad/0x340
? switched_from_dl+0x2d0/0x2d0
__run_hrtimer+0x8a/0x1a0
__hrtimer_run_queues+0x91/0x130
hrtimer_interrupt+0x10f/0x220
__sysvec_apic_timer_interrupt+0x7b/0xd0
sysvec_apic_timer_interrupt+0x4f/0xd0
? asm_sysvec_apic_timer_interrupt+0xa/0x20
asm_sysvec_apic_timer_interrupt+0x12/0x20
RIP: 0033:0x7fff196bf6f5
Instead of calling __put_task_struct() directly, we defer it using
call_rcu(). A more natural approach would use a workqueue, but since
in PREEMPT_RT, we can't allocate dynamic memory from atomic context,
the code would become more complex because we would need to put the
work_struct instance in the task_struct and initialize it when we
allocate a new task_struct.
Changelog
=========
v1:
* Initial implementation fixing the splat.
v2:
* Isolate the logic in its own function.
* Fix two more cases caught in review.
v3:
* Change __put_task_struct() to handle the issue internally.
v4:
* Explain why call_rcu() is safe to call from interrupt context.
Signed-off-by: Wander Lairson Costa <wander@...hat.com>
Reported-by: Hu Chunyu <chuhu@...hat.com>
Suggested-by: Oleg Nesterov <oleg@...hat.com>
Suggested-by: Valentin Schneider <vschneid@...hat.com>
Cc: Paul McKenney <paulmck@...nel.org>
---
kernel/fork.c | 25 ++++++++++++++++++++++++-
1 file changed, 24 insertions(+), 1 deletion(-)
diff --git a/kernel/fork.c b/kernel/fork.c
index 9f7fe3541897..532dd2ceb6a3 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -840,7 +840,7 @@ static inline void put_signal_struct(struct signal_struct *sig)
free_signal_struct(sig);
}
-void __put_task_struct(struct task_struct *tsk)
+static void ___put_task_struct(struct task_struct *tsk)
{
WARN_ON(!tsk->exit_state);
WARN_ON(refcount_read(&tsk->usage));
@@ -857,6 +857,29 @@ void __put_task_struct(struct task_struct *tsk)
sched_core_free(tsk);
free_task(tsk);
}
+
+static void delayed_put_task_struct_rcu(struct rcu_head *rhp)
+{
+ struct task_struct *task = container_of(rhp, struct task_struct, rcu);
+
+ ___put_task_struct(task);
+}
+
+void __put_task_struct(struct task_struct *tsk)
+{
+ if (IS_ENABLED(CONFIG_PREEMPT_RT) && (!preemptible() || !in_task()))
+ /*
+ * under PREEMPT_RT, we can't call put_task_struct
+ * in atomic context because it will indirectly
+ * acquire sleeping locks.
+ *
+ * call_rcu() will schedule delayed_put_task_struct_rcu()
+ * to be called in process context.
+ */
+ call_rcu(&tsk->rcu, delayed_put_task_struct_rcu);
+ else
+ ___put_task_struct(tsk);
+}
EXPORT_SYMBOL_GPL(__put_task_struct);
void __init __weak arch_task_cache_init(void) { }
--
2.39.1
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