From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Sasha Levin <sashal@kernel.org>, frederic@kernel.org,
        paulmck@kernel.org, mingo@redhat.com, will@kernel.org,
        pmladek@suse.com, keescook@chromium.org, mcgrof@kernel.org,
        akpm@linux-foundation.org, gpiccoli@igalia.com,
        daniel.vetter@ffwll.ch, davidgow@google.com,
        tangmeng@uniontech.com, yangtiezhu@loongson.cn,
        mark.rutland@arm.com, jpoimboe@kernel.org, mpe@ellerman.id.au,
        svens@linux.ibm.com
Subject: [PATCH AUTOSEL 6.1 20/21] cpuidle: lib/bug: Disable rcu_is_watching() during WARN/BUG
Date:   Sat, 25 Feb 2023 22:42:55 -0500
Message-Id: <20230226034256.771769-20-sashal@kernel.org>
In-Reply-To: <20230226034256.771769-1-sashal@kernel.org>
References: <20230226034256.771769-1-sashal@kernel.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
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From: Peter Zijlstra <peterz@infradead.org>

[ Upstream commit 5a5d7e9badd2cb8065db171961bd30bd3595e4b6 ]

In order to avoid WARN/BUG from generating nested or even recursive
warnings, force rcu_is_watching() true during
WARN/lockdep_rcu_suspicious().

Notably things like unwinding the stack can trigger rcu_dereference()
warnings, which then triggers more unwinding which then triggers more
warnings etc..

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230126151323.408156109@infradead.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/linux/context_tracking.h | 27 +++++++++++++++++++++++++++
 kernel/locking/lockdep.c         |  3 +++
 kernel/panic.c                   |  5 +++++
 lib/bug.c                        | 15 ++++++++++++++-
 4 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index dcef4a9e4d63e..d4afa8508a806 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -130,9 +130,36 @@ static __always_inline unsigned long ct_state_inc(int incby)
 	return arch_atomic_add_return(incby, this_cpu_ptr(&context_tracking.state));
 }
 
+static __always_inline bool warn_rcu_enter(void)
+{
+	bool ret = false;
+
+	/*
+	 * Horrible hack to shut up recursive RCU isn't watching fail since
+	 * lots of the actual reporting also relies on RCU.
+	 */
+	preempt_disable_notrace();
+	if (rcu_dynticks_curr_cpu_in_eqs()) {
+		ret = true;
+		ct_state_inc(RCU_DYNTICKS_IDX);
+	}
+
+	return ret;
+}
+
+static __always_inline void warn_rcu_exit(bool rcu)
+{
+	if (rcu)
+		ct_state_inc(RCU_DYNTICKS_IDX);
+	preempt_enable_notrace();
+}
+
 #else
 static inline void ct_idle_enter(void) { }
 static inline void ct_idle_exit(void) { }
+
+static __always_inline bool warn_rcu_enter(void) { return false; }
+static __always_inline void warn_rcu_exit(bool rcu) { }
 #endif /* !CONFIG_CONTEXT_TRACKING_IDLE */
 
 #endif
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index e3375bc40dadc..50d4863974e7a 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -55,6 +55,7 @@
 #include <linux/rcupdate.h>
 #include <linux/kprobes.h>
 #include <linux/lockdep.h>
+#include <linux/context_tracking.h>
 
 #include <asm/sections.h>
 
@@ -6555,6 +6556,7 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
 {
 	struct task_struct *curr = current;
 	int dl = READ_ONCE(debug_locks);
+	bool rcu = warn_rcu_enter();
 
 	/* Note: the following can be executed concurrently, so be careful. */
 	pr_warn("\n");
@@ -6595,5 +6597,6 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
 	lockdep_print_held_locks(curr);
 	pr_warn("\nstack backtrace:\n");
 	dump_stack();
+	warn_rcu_exit(rcu);
 }
 EXPORT_SYMBOL_GPL(lockdep_rcu_suspicious);
diff --git a/kernel/panic.c b/kernel/panic.c
index 7834c9854e026..5864f356ee576 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -33,6 +33,7 @@
 #include <linux/ratelimit.h>
 #include <linux/debugfs.h>
 #include <linux/sysfs.h>
+#include <linux/context_tracking.h>
 #include <trace/events/error_report.h>
 #include <asm/sections.h>
 
@@ -678,6 +679,7 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
 void warn_slowpath_fmt(const char *file, int line, unsigned taint,
 		       const char *fmt, ...)
 {
+	bool rcu = warn_rcu_enter();
 	struct warn_args args;
 
 	pr_warn(CUT_HERE);
@@ -692,11 +694,13 @@ void warn_slowpath_fmt(const char *file, int line, unsigned taint,
 	va_start(args.args, fmt);
 	__warn(file, line, __builtin_return_address(0), taint, NULL, &args);
 	va_end(args.args);
+	warn_rcu_exit(rcu);
 }
 EXPORT_SYMBOL(warn_slowpath_fmt);
 #else
 void __warn_printk(const char *fmt, ...)
 {
+	bool rcu = warn_rcu_enter();
 	va_list args;
 
 	pr_warn(CUT_HERE);
@@ -704,6 +708,7 @@ void __warn_printk(const char *fmt, ...)
 	va_start(args, fmt);
 	vprintk(fmt, args);
 	va_end(args);
+	warn_rcu_exit(rcu);
 }
 EXPORT_SYMBOL(__warn_printk);
 #endif
diff --git a/lib/bug.c b/lib/bug.c
index c223a2575b721..e0ff219899902 100644
--- a/lib/bug.c
+++ b/lib/bug.c
@@ -47,6 +47,7 @@
 #include <linux/sched.h>
 #include <linux/rculist.h>
 #include <linux/ftrace.h>
+#include <linux/context_tracking.h>
 
 extern struct bug_entry __start___bug_table[], __stop___bug_table[];
 
@@ -153,7 +154,7 @@ struct bug_entry *find_bug(unsigned long bugaddr)
 	return module_find_bug(bugaddr);
 }
 
-enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
+static enum bug_trap_type __report_bug(unsigned long bugaddr, struct pt_regs *regs)
 {
 	struct bug_entry *bug;
 	const char *file;
@@ -209,6 +210,18 @@ enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
 	return BUG_TRAP_TYPE_BUG;
 }
 
+enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
+{
+	enum bug_trap_type ret;
+	bool rcu = false;
+
+	rcu = warn_rcu_enter();
+	ret = __report_bug(bugaddr, regs);
+	warn_rcu_exit(rcu);
+
+	return ret;
+}
+
 static void clear_once_table(struct bug_entry *start, struct bug_entry *end)
 {
 	struct bug_entry *bug;
-- 
2.39.0