Date:   Wed, 28 Dec 2022 09:45:11 +0800
From:   Zhen Lei <thunder.leizhen@...wei.com>
To:     Petr Mladek <pmladek@...e.com>, <linux-kernel@...r.kernel.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        <linux-modules@...r.kernel.org>
CC:     Zhen Lei <thunder.leizhen@...wei.com>,
        Anders Roxell <anders.roxell@...aro.org>
Subject: [PATCH v2] kallsyms: Fix sleeping function called from invalid context when CONFIG_KALLSYMS_SELFTEST=y

[T58] BUG: sleeping function called from invalid context at kernel/kallsyms.c:305
[T58] in_atomic(): 0, irqs_disabled(): 128, non_block: 0, pid: 58, name: kallsyms_test
[T58] preempt_count: 0, expected: 0
[T58] RCU nest depth: 0, expected: 0
[T58] no locks held by kallsyms_test/58.
[T58] irq event stamp: 18899904
[T58] hardirqs last enabled at (18899903): finish_task_switch.isra.0 (core.c:?)
[T58] hardirqs last disabled at (18899904): test_perf_kallsyms_on_each_symbol (kallsyms_selftest.c:?)
[T58] softirqs last enabled at (18899886): __do_softirq (??:?)
[T58] softirqs last disabled at (18899879): ____do_softirq (irq.c:?)
[T58] CPU: 0 PID: 58 Comm: kallsyms_test Tainted: G T  6.1.0-next-20221215 #2
[T58] Hardware name: linux,dummy-virt (DT)
[T58] Call trace:
[T58] dump_backtrace (??:?)
[T58] show_stack (??:?)
[T58] dump_stack_lvl (??:?)
[T58] dump_stack (??:?)
[T58] __might_resched (??:?)
[T58] kallsyms_on_each_symbol (??:?)
[T58] test_perf_kallsyms_on_each_symbol (kallsyms_selftest.c:?)
[T58] test_entry (kallsyms_selftest.c:?)
[T58] kthread (kthread.c:?)
[T58] ret_from_fork (??:?)
[T58] kallsyms_selftest: kallsyms_on_each_symbol() traverse all: 5744310840 ns
[T58] kallsyms_selftest: kallsyms_on_each_match_symbol() traverse all: 1164580 ns
[T58] kallsyms_selftest: finish

The execution time of function kallsyms_on_each_match_symbol() is very
short, about ten microseconds, the probability of this process being
interrupted is very small. And even if it happens, we just have to try
again.

The execution time of function kallsyms_on_each_symbol() is very long,
it takes tens of milliseconds, context switches is likely occur during
this period. If the time obtained by task_cputime() is accurate, it is
preferred. Otherwise, use local_clock() directly, and the time taken by
irqs and high-priority tasks is not deducted because they are always
running for a short time.

Fixes: 30f3bb09778d ("kallsyms: Add self-test facility")
Reported-by: Anders Roxell <anders.roxell@...aro.org>
Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
---
 kernel/kallsyms_selftest.c | 52 +++++++++++++++++++++++++++-----------
 1 file changed, 37 insertions(+), 15 deletions(-)

v1 --> v2:
1. Keep calling cond_resched() when CONFIG_KALLSYMS_SELFTEST=y. Instead,
   function kallsyms_on_each_match_symbol() and kallsyms_on_each_symbol()
   are not protected by local_irq_save() in kallsyms_selftest.c.

diff --git a/kernel/kallsyms_selftest.c b/kernel/kallsyms_selftest.c
index f35d9cc1aab1544..9c94f06aa951971 100644
--- a/kernel/kallsyms_selftest.c
+++ b/kernel/kallsyms_selftest.c
@@ -12,9 +12,11 @@
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/kallsyms.h>
+#include <linux/kernel_stat.h>
+#include <linux/kthread.h>
 #include <linux/random.h>
 #include <linux/sched/clock.h>
-#include <linux/kthread.h>
+#include <linux/sched/cputime.h>
 #include <linux/vmalloc.h>
 
 #include "kallsyms_internal.h"
@@ -161,9 +163,9 @@ static int lookup_name(void *data, const char *name, struct module *mod, unsigne
 	struct test_stat *stat = (struct test_stat *)data;
 
 	local_irq_save(flags);
-	t0 = sched_clock();
+	t0 = local_clock();
 	(void)kallsyms_lookup_name(name);
-	t1 = sched_clock();
+	t1 = local_clock();
 	local_irq_restore(flags);
 
 	t = t1 - t0;
@@ -233,19 +235,30 @@ static int find_symbol(void *data, const char *name, struct module *mod, unsigne
 
 static void test_perf_kallsyms_on_each_symbol(void)
 {
-	u64 t0, t1;
-	unsigned long flags;
+	bool accurate;
+	u64 utime, t0, t1;
 	struct test_stat stat;
 
 	memset(&stat, 0, sizeof(stat));
 	stat.max = INT_MAX;
 	stat.name = stub_name;
 	stat.perf = 1;
-	local_irq_save(flags);
-	t0 = sched_clock();
+
+	/*
+	 * This test process takes tens of milliseconds, context switches may
+	 * occur during this period. If task_cputime() returns true, it is
+	 * accurate enough. Otherwise, use local_clock() directly. This is
+	 * based on the assumption that irqs and high-priority tasks are always
+	 * running for a short time, they may cause less error.
+	 */
+	accurate = task_cputime(current, &utime, &t0);
+	if (!accurate)
+		t0 = local_clock();
 	kallsyms_on_each_symbol(find_symbol, &stat);
-	t1 = sched_clock();
-	local_irq_restore(flags);
+	if (accurate)
+		task_cputime(current, &utime, &t1);
+	else
+		t1 = local_clock();
 	pr_info("kallsyms_on_each_symbol() traverse all: %lld ns\n", t1 - t0);
 }
 
@@ -270,17 +283,26 @@ static int match_symbol(void *data, unsigned long addr)
 static void test_perf_kallsyms_on_each_match_symbol(void)
 {
 	u64 t0, t1;
-	unsigned long flags;
+	int cpu = smp_processor_id();
+	unsigned long nr_irqs;
 	struct test_stat stat;
 
 	memset(&stat, 0, sizeof(stat));
 	stat.max = INT_MAX;
 	stat.name = stub_name;
-	local_irq_save(flags);
-	t0 = sched_clock();
-	kallsyms_on_each_match_symbol(match_symbol, stat.name, &stat);
-	t1 = sched_clock();
-	local_irq_restore(flags);
+
+	/*
+	 * The test thread has been bound to a fixed CPU in advance. If the
+	 * number of irqs does not change, no new scheduling request will be
+	 * generated. That is, the performance test process is atomic.
+	 */
+	do {
+		nr_irqs = kstat_cpu_irqs_sum(cpu);
+		cond_resched();
+		t0 = local_clock();
+		kallsyms_on_each_match_symbol(match_symbol, stat.name, &stat);
+		t1 = local_clock();
+	} while (nr_irqs != kstat_cpu_irqs_sum(cpu));
 	pr_info("kallsyms_on_each_match_symbol() traverse all: %lld ns\n", t1 - t0);
 }
 
-- 
2.25.1

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