linux-kernel - [PATCH] rcu: Fix suspicious RCU usage in __do

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Message-Id: <20240427102808.29356-1-qiang.zhang1211@gmail.com>
Date: Sat, 27 Apr 2024 18:28:08 +0800
From: Zqiang <qiang.zhang1211@...il.com>
To: paulmck@...nel.org,
	tglx@...utronix.de,
	frederic@...nel.org,
	neeraj.upadhyay@...nel.org,
	joel@...lfernandes.org
Cc: qiang.zhang1211@...il.com,
	rcu@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] rcu: Fix suspicious RCU usage in __do_softirq()

Currently, the condition "__this_cpu_read(ksoftirqd) == current" is
checked to ensure the rcu_softirq_qs() is invoked in ksoftirqd tasks
context for non-RT kernels. however, in some scenarios, this condition
will be broken.

     ksoftirqd/0
->finish_task_switch
  ->put_task_struct_rcu_user
    ->call_rcu(&task->rcu, delayed_put_task_struct)
      ->__kasan_record_aux_stack
        ->pfn_valid
          ->rcu_read_lock_sched()
            <interrupt>
             __irq_exit_rcu
             ->__do_softirq
               -> if (!IS_ENABLED(CONFIG_PREEMPT_RT) &&
                   __this_cpu_read(ksoftirqd) == current)
                   ->rcu_softirq_qs
                     ->RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map))

The rcu quiescent states is reported occurs in the rcu-read critical
section, so the lockdep warning is triggered. this commit therefore
remove "__this_cpu_read(ksoftirqd) == current" condition check, generate
new "handle_softirqs(bool kirqd)" function to replace __do_softirq() in
run_ksoftirqdt(), and set parameter kirqd to true, make rcu_softirq_qs()
be invoked only in ksofirqd tasks context for non-RT kernels.

Reported-by: syzbot+dce04ed6d1438ad69656@...kaller.appspotmail.com
Link: https://lore.kernel.org/lkml/8f281a10-b85a-4586-9586-5bbc12dc784f@paulmck-laptop/T/#mea8aba4abfcb97bbf499d169ce7f30c4cff1b0e3
Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Zqiang <qiang.zhang1211@...il.com>
---
 kernel/softirq.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index b315b21fb28c..e991d735be0d 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -508,7 +508,7 @@ static inline bool lockdep_softirq_start(void) { return false; }
 static inline void lockdep_softirq_end(bool in_hardirq) { }
 #endif
 
-asmlinkage __visible void __softirq_entry __do_softirq(void)
+static void handle_softirqs(bool kirqd)
 {
 	unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
 	unsigned long old_flags = current->flags;
@@ -563,8 +563,7 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
 		pending >>= softirq_bit;
 	}
 
-	if (!IS_ENABLED(CONFIG_PREEMPT_RT) &&
-	    __this_cpu_read(ksoftirqd) == current)
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT) && kirqd)
 		rcu_softirq_qs();
 
 	local_irq_disable();
@@ -584,6 +583,11 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
 	current_restore_flags(old_flags, PF_MEMALLOC);
 }
 
+asmlinkage __visible void __softirq_entry __do_softirq(void)
+{
+	handle_softirqs(false);
+}
+
 /**
  * irq_enter_rcu - Enter an interrupt context with RCU watching
  */
@@ -921,7 +925,7 @@ static void run_ksoftirqd(unsigned int cpu)
 		 * We can safely run softirq on inline stack, as we are not deep
 		 * in the task stack here.
 		 */
-		__do_softirq();
+		handle_softirqs(true);
 		ksoftirqd_run_end();
 		cond_resched();
 		return;
-- 
2.17.1