[PATCH AUTOSEL 6.1 20/21] cpuidle: lib/bug: Disable rcu_is_watching() during WARN/BUG

Sasha Levin
2023-02-26T03:45:26Z

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