linux-kernel - Re: [syzbot] [bpf?] [net?] INFO: rcu detected stall in handle

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Date: Sat, 11 May 2024 19:06:14 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+afcbef13b9fa6ae41f9a@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [bpf?] [net?] INFO: rcu detected stall in handle_softirqs

On Sat, 11 May 2024 00:31:21 -0700
> syzbot found the following issue on:
> 
> HEAD commit:    ee5b455b0ada Merge tag 'slab-for-6.9-rc7-fixes' of git://g..
> git tree:       upstream
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=105fcb4b180000

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git  ee5b455b0ada

--- x/kernel/softirq.c
+++ y/kernel/softirq.c
@@ -517,6 +517,7 @@ static void handle_softirqs(bool ksirqd)
 	bool in_hardirq;
 	__u32 pending;
 	int softirq_bit;
+	unsigned long lt = 0;
 
 	/*
 	 * Mask out PF_MEMALLOC as the current task context is borrowed for the
@@ -542,6 +543,7 @@ restart:
 	while ((softirq_bit = ffs(pending))) {
 		unsigned int vec_nr;
 		int prev_count;
+		unsigned long t1, t2;
 
 		h += softirq_bit - 1;
 
@@ -551,7 +553,14 @@ restart:
 		kstat_incr_softirqs_this_cpu(vec_nr);
 
 		trace_softirq_entry(vec_nr);
+		t1 = jiffies;
 		h->action(h);
+		t2 = jiffies;
+		if (t1 + 2 < t2)
+			break;
+		lt += t2 - t1;
+		if (lt > 200)
+			break;
 		trace_softirq_exit(vec_nr);
 		if (unlikely(prev_count != preempt_count())) {
 			pr_err("huh, entered softirq %u %s %p with preempt_count %08x, exited with %08x?\n",
--