From a5dec9f82ab2ae486119f0b0820ea16db3e522c3 Mon Sep 17 00:00:00 2001
From: Frederic Weisbecker <frederic@kernel.org>
Date: Mon, 26 Jul 2021 14:55:08 +0200
Subject: [PATCH] posix-cpu-timers: Assert task sighand is locked while starting cputime counter
Git-commit: a5dec9f82ab2ae486119f0b0820ea16db3e522c3
Patch-mainline: v5.15-rc1
References: bsc#1190366
Starting the process wide cputime counter needs to be done in the same
sighand locking sequence than actually arming the related timer otherwise
this races against concurrent timers setting/expiring in the same
threadgroup.
Detecting that the cputime counter is started without holding the sighand
lock is a first step toward debugging such situations.
Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210726125513.271824-2-frederic@kernel.org
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
include/linux/sched/signal.h | 6 ++++++
kernel/signal.c | 15 +++++++++++++++
kernel/time/posix-cpu-timers.c | 2 ++
3 files changed, 23 insertions(+)
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index b9126fe06c3f..0310a5add9ab 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -714,6 +714,12 @@ static inline void unlock_task_sighand(struct task_struct *task,
spin_unlock_irqrestore(&task->sighand->siglock, *flags);
}
+#ifdef CONFIG_LOCKDEP
+extern void lockdep_assert_task_sighand_held(struct task_struct *task);
+#else
+static inline void lockdep_assert_task_sighand_held(struct task_struct *task) { }
+#endif
+
static inline unsigned long task_rlimit(const struct task_struct *task,
unsigned int limit)
{
diff --git a/kernel/signal.c b/kernel/signal.c
index a3229add4455..52b6abec0ff8 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1413,6 +1413,21 @@ struct sighand_struct *__lock_task_sighand(struct task_struct *tsk,
return sighand;
}
+#ifdef CONFIG_LOCKDEP
+void lockdep_assert_task_sighand_held(struct task_struct *task)
+{
+ struct sighand_struct *sighand;
+
+ rcu_read_lock();
+ sighand = rcu_dereference(task->sighand);
+ if (sighand)
+ lockdep_assert_held(&sighand->siglock);
+ else
+ WARN_ON_ONCE(1);
+ rcu_read_unlock();
+}
+#endif
+
/*
* send signal info to all the members of a group
*/
diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 517be7fd175e..4693d3c71e7e 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -291,6 +291,8 @@ static void thread_group_start_cputime(struct task_struct *tsk, u64 *samples)
struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
struct posix_cputimers *pct = &tsk->signal->posix_cputimers;
+ lockdep_assert_task_sighand_held(tsk);
+
/* Check if cputimer isn't running. This is accessed without locking. */
if (!READ_ONCE(pct->timers_active)) {
struct task_cputime sum;
--
2.26.2