Kernel space lock contention配置及其使用

最新推荐文章于 2025-09-06 10:01:27 发布

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最新推荐文章于 2025-09-06 10:01:27 发布 · 2.4k 阅读

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本文详细介绍Linux内核中锁调试的配置与使用，包括lock contention的跟踪、lock trace event的捕获及proc节点信息的解析，为解决锁竞争和死锁问题提供有效手段。

概述

本文涉及到的内容如下：

kernel lock相关debug方式，比如lock耗时，拿不到lock，lock依赖等等
trace的使用

1.开启lock contenttion涉及到的config配置

config LOCKDEP  
        bool  
        depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT  
        select STACKTRACE  
        select FRAME_POINTER if !MIPS && !PPC && !ARM_UNWIND && !S390 && !MICROBLAZE && !ARC && !SCORE && !X86  
        select KALLSYMS  
        select KALLSYMS_ALL  
  
config LOCKDEP_SMALL  
        bool  
  
config LOCK_STAT  
        bool "Lock usage statistics"  
        depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT  
        select LOCKDEP  
        select DEBUG_SPINLOCK  
        select DEBUG_MUTEXES  
        select DEBUG_RT_MUTEXES if RT_MUTEXES  
        select DEBUG_LOCK_ALLOC  
        default n  
        help  
         This feature enables tracking lock contention points  
  
         For more details, see Documentation/locking/lockstat.txt  
  
         This also enables lock events required by "perf lock",  
         subcommand of perf.  
         If you want to use "perf lock", you also need to turn on  
         CONFIG_EVENT_TRACING.  
  
         CONFIG_LOCK_STAT defines "contended" and "acquired" lock events.  
         (CONFIG_LOCKDEP defines "acquire" and "release" events.)

上面的config默认是关闭状态。

2 menuconfig开启config配置

kernel hacking —> Lock Debugging (spinlock, mutexs, etc…) —>进入之后勾选
Lock Debugging: detect incorrect freeing of live locks 和Lcok usage statistics,就会把依赖项自动勾选.
在这里插入图片描述

保存退出之后,可以查看kernel下面新产生的config diff文件：

# Lock Debugging (spinlocks, mutexes, etc...)  
 #  
-# CONFIG_DEBUG_RT_MUTEXES is not set  
-# CONFIG_DEBUG_SPINLOCK is not set  
-# CONFIG_DEBUG_MUTEXES is not set  
+CONFIG_DEBUG_RT_MUTEXES=y  
+CONFIG_DEBUG_SPINLOCK=y  
+CONFIG_DEBUG_MUTEXES=y  
 # CONFIG_DEBUG_WW_MUTEX_SLOWPATH is not set  
-# CONFIG_DEBUG_LOCK_ALLOC is not set  
+CONFIG_DEBUG_LOCK_ALLOC=y  
 # CONFIG_PROVE_LOCKING is not set  
-# CONFIG_LOCK_STAT is not set  
+CONFIG_LOCKDEP=y  
+CONFIG_LOCK_STAT=y  
+# CONFIG_DEBUG_LOCKDEP is not set  
 # CONFIG_DEBUG_ATOMIC_SLEEP is not set  
 # CONFIG_DEBUG_LOCKING_API_SELFTESTS is not set  
 # CONFIG_LOCK_TORTURE_TEST is not set

这样开启lock trace event了.。编译boot并刷机即可！

3 确定是否开启trace lock content feature

上面步骤二中开启之后,在adb shell里面多了如下几个接口：

增加了lock trace event, 有四个lock trace event,具体做什么使用,下面在详细讲解
增加了lock的统计信息, 节点信息实现源码kernel/locking/lockdep_proc.c文件中:
● lock_stat: 统计各种类型lock的时延
● lockdep: 表示锁的的深度,即一个lock里面调用了多少个lock,并将这些lock的调用全部显示出来
● lockdep_stats: 即锁深度里面包含了哪些lock以及频次
● locks:锁的状态,这个实现在fs/locks.c文件里面

在这里插入图片描述

4 如何使用lock trace event和proc node信息

4.1 lock trace event

从第三部分可以知道,lock trace event包含四个event,分别讲解如下:
四个event定义在include/trace/event/lock.h里面, 使用在kernel/locking/lockdep.c文件,

lock_acquire: 获取lock,比如mutex lock ,rcu read lock 或者spinlock等等lock
lock_acquired: 表示已经获取lock了
lock_release: lock释放的event
lock_contended: lock被谁hold了

那么如何抓取lock相关的trace event呢?
可以使用下面的脚本抓取(必须添加lock event )，即正常的抓取trace 命令：

●	echo 40000 > buffer_size_kb && echo irq sched_switch sched_wakeup sched_waking cpu_frequency cpu_idle lock > set_event && cat set_event && echo > trace  && echo 1 > tracing_on && sleep 10 && echo 0 > tracing_on && cat trace > /data/trace.txt

脚本执行完毕之后, pull出data目录下的trace.txt文件,vim打开即可看到下面类似的信息：

┊   ┊  sleep-2875  [004] d.s2   748.861607: sched_waking: comm=rcu_sched pid=9 prio=120 target_cpu=000  
┊   ┊  sleep-2875  [004] d.s3   748.861608: lock_acquire: 00000000d4eff177 &rq->lock  
┊   ┊  sleep-2875  [004] d.s3   748.861609: lock_contended: 00000000d4eff177 &rq->lock  
┊   ┊  sleep-2875  [004] d.s3   748.861662: lock_acquired: 00000000d4eff177 &rq->lock  
┊   ┊  sleep-2875  [004] d.s3   748.861663: lock_acquire: 000000000ff04d65 read tk_core.seq  
┊   ┊  sleep-2875  [004] d.s3   748.861664: lock_release: 000000000ff04d65 tk_core.seq  
┊   ┊  sleep-2875  [004] d.s3   748.861666: lock_acquire: 00000000cc726398 read rcu_read_lock  
┊   ┊  sleep-2875  [004] d.s3   748.861667: lock_release: 00000000cc726398 rcu_read_lock  
┊   ┊  sleep-2875  [004] d.s3   748.861668: lock_release: 00000000d4eff177 &rq->lock  
┊   ┊  sleep-2875  [004] d.s2   748.861669: lock_acquire: 00000000cc726398 read rcu_read_lock  
┊   ┊  sleep-2875  [004] d.s2   748.861670: lock_acquire: 00000000cc726398 read rcu_read_lock  
┊   ┊  sleep-2875  [004] d.s2   748.861671: lock_release: 00000000cc726398 rcu_read_lock  
┊   ┊  sleep-2875  [004] d.s2   748.861672: lock_acquire: 00000000cc726398 read rcu_read_lock  
┊   ┊  sleep-2875  [004] d.s2   748.861673: lock_release: 00000000cc726398 rcu_read_lock  
┊   ┊  sleep-2875  [004] d.s2   748.861674: lock_acquire: 00000000cc726398 read rcu_read_lock  
┊   ┊  sleep-2875  [004] d.s2   748.861675: lock_release: 00000000cc726398 rcu_read_lock  
┊   ┊  sleep-2875  [004] d.s2   748.861676: lock_acquire: 00000000cc726398 read rcu_read_lock  
┊   ┊  sleep-2875  [004] d.s2   748.861677: lock_release: 00000000cc726398 rcu_read_lock  
┊   ┊  sleep-2875  [004] d.s2   748.861678: lock_acquire: 00000000cc726398 read rcu_read_lock  
┊   ┊  sleep-2875  [004] d.s2   748.861679: lock_release: 00000000cc726