增加等IO状态的唤醒堆栈打印及缺页异常导致iowait分析

一、背景

在之前的博客 在计算进程D状态持续时间及等IO的时间遇到的一处问题-CSDN博客 里，我们修复了一处在抓取D状态及等IO状态堆栈的监控程序的一处时间计算bug，在这篇博客里，我们进一步丰富监控程序，在进程iodelay被唤醒时，增加是谁最终唤醒的处于in_iowait状态下的进程，这样可以有助于判断是什么原因进入的in_iowait状态。有关iodelay及iowait的概念见之前的博客 获取进程或线程级别的iodelay的方法-CSDN博客 和 cpu的iowait指标解释及示例-CSDN博客 。在第二章里，我们给出修改后的源码，并做一些解释。然后在第三章里，我们利用修改后的程序，分析一处缺页异常导致iowait的例子，做原理分析。

另外，需要强调的是，并不是所有等io的进程的状态都是D的，即等io的进程状态除了可能是TASK_UNINTERRUPTIBLE，也可能是TASK_KILLABLE状态的，这一点，我们会在 2.3 一节和 3.3 一节里进行说明。

二、增加等IO状态的唤醒堆栈打印

2.1 修改后的完整源码

#include <linux/module.h>
#include <linux/capability.h>
#include <linux/sched.h>
#include <linux/uaccess.h>
#include <linux/proc_fs.h>
#include <linux/ctype.h>
#include <linux/seq_file.h>
#include <linux/poll.h>
#include <linux/types.h>
#include <linux/ioctl.h>
#include <linux/errno.h>
#include <linux/stddef.h>
#include <linux/lockdep.h>
#include <linux/kthread.h>
#include <linux/sched.h>
#include <linux/delay.h>
#include <linux/wait.h>
#include <linux/init.h>
#include <asm/atomic.h>
#include <trace/events/workqueue.h>
#include <linux/sched/clock.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/tracepoint.h>
#include <trace/events/osmonitor.h>
#include <trace/events/sched.h>
#include <trace/events/irq.h>
#include <trace/events/kmem.h>
#include <linux/ptrace.h>
#include <linux/uaccess.h>
#include <asm/processor.h>
#include <linux/sched/task_stack.h>
#include <linux/nmi.h>
#include <asm/apic.h>
#include <linux/version.h>
#include <linux/sched/mm.h>
#include <asm/irq_regs.h>
#include <linux/kallsyms.h>
#include <linux/kprobes.h>
#include <linux/stop_machine.h>MODULE_LICENSE("GPL");
MODULE_AUTHOR("zhaoxin");
MODULE_DESCRIPTION("Module for monitor D tasks.");
MODULE_VERSION("1.0");#define IODELAY_TRACEPOINT_ENABLE#define TEST_STACK_TRACE_ENTRIES   32typedef unsigned int (*stack_trace_save_tsk_func)(struct task_struct *task,unsigned long *store, unsigned int size,unsigned int skipnr);
stack_trace_save_tsk_func _stack_trace_save_tsk;typedef int (*get_cmdline_func)(struct task_struct *task, char *buffer, int buflen);
get_cmdline_func _get_cmdline_func;#define TESTDIOMONITOR_SAMPLEDESC_SWDSTART  "swDstart"
#define TESTDIOMONITOR_SAMPLEDESC_WADSTOP    "waDstop"
#define TESTDIOMONITOR_SAMPLEDESC_SWDIOSTART "swDiostart"
#define TESTDIOMONITOR_SAMPLEDESC_WADIOSTOP  "waDiostop"
#define TESTDIOMONITOR_SAMPLEDESC_DEXCEED    "Dexceed"
#define TESTDIOMONITOR_SAMPLEDESC_DIOEXCEED  "Dioexceed"
#define TESTDIOMONITOR_SAMPLEDESC_IOEXCEED   "Ioexceed"#define TESTDIOMONITOR_SIMPLE#ifdef TESTDIOMONITOR_SIMPLE
#define TESTDIOMONITOR_SIMPLE_THRESHOLDNS   0ull//5000000ull
#endif// 1ms
//#define TESTDIOMONITOR_DEXCEED_THRESHOLD     1000ull//1000000ullstruct uclamp_bucket {unsigned long value : bits_per(SCHED_CAPACITY_SCALE);unsigned long tasks : BITS_PER_LONG - bits_per(SCHED_CAPACITY_SCALE);
};struct uclamp_rq {unsigned int value;struct uclamp_bucket bucket[UCLAMP_BUCKETS];
};/* CFS-related fields in a runqueue */
struct cfs_rq {struct load_weight	load;unsigned int		nr_running;unsigned int		h_nr_running;      /* SCHED_{NORMAL,BATCH,IDLE} */unsigned int		idle_nr_running;   /* SCHED_IDLE */unsigned int		idle_h_nr_running; /* SCHED_IDLE */u64			exec_clock;u64			min_vruntime;
#ifdef CONFIG_SCHED_COREunsigned int		forceidle_seq;u64			min_vruntime_fi;
#endif#ifndef CONFIG_64BITu64			min_vruntime_copy;
#endifstruct rb_root_cached	tasks_timeline;/** 'curr' points to currently running entity on this cfs_rq.* It is set to NULL otherwise (i.e when none are currently running).*/struct sched_entity	*curr;struct sched_entity	*next;struct sched_entity	*last;struct sched_entity	*skip;#ifdef	CONFIG_SCHED_DEBUGunsigned int		nr_spread_over;
#endif#ifdef CONFIG_SMP/** CFS load tracking*/struct sched_avg	avg;
#ifndef CONFIG_64BITu64			last_update_time_copy;
#endifstruct {raw_spinlock_t	lock ____cacheline_aligned;int		nr;unsigned long	load_avg;unsigned long	util_avg;unsigned long	runnable_avg;} removed;#ifdef CONFIG_FAIR_GROUP_SCHEDunsigned long		tg_load_avg_contrib;long			propagate;long			prop_runnable_sum;/**   h_load = weight * f(tg)** Where f(tg) is the recursive weight fraction assigned to* this group.*/unsigned long		h_load;u64			last_h_load_update;struct sched_entity	*h_load_next;
#endif /* CONFIG_FAIR_GROUP_SCHED */
#endif /* CONFIG_SMP */#ifdef CONFIG_FAIR_GROUP_SCHEDstruct rq		*rq;	/* CPU runqueue to which this cfs_rq is attached *//** leaf cfs_rqs are those that hold tasks (lowest schedulable entity in* a hierarchy). Non-leaf lrqs hold other higher schedulable entities* (like users, containers etc.)** leaf_cfs_rq_list ties together list of leaf cfs_rq's in a CPU.* This list is used during load balance.*/int			on_list;struct list_head	leaf_cfs_rq_list;struct task_group	*tg;	/* group that "owns" this runqueue *//* Locally cached copy of our task_group's idle value */int			idle;#ifdef CONFIG_CFS_BANDWIDTHint			runtime_enabled;s64			runtime_remaining;u64			throttled_pelt_idle;
#ifndef CONFIG_64BITu64                     throttled_pelt_idle_copy;
#endifu64			throttled_clock;u64			throttled_clock_pelt;u64			throttled_clock_pelt_time;int			throttled;int			throttle_count;struct list_head	throttled_list;
#ifdef CONFIG_SMPstruct list_head	throttled_csd_list;
#endif
#endif /* CONFIG_CFS_BANDWIDTH */
#endif /* CONFIG_FAIR_GROUP_SCHED */
};struct rt_prio_array {DECLARE_BITMAP(bitmap, MAX_RT_PRIO+1); /* include 1 bit for delimiter */struct list_head queue[MAX_RT_PRIO];
};/* Real-Time classes' related field in a runqueue: */
struct rt_rq {struct rt_prio_array	active;unsigned int		rt_nr_running;unsigned int		rr_nr_running;
#if defined CONFIG_SMP || defined CONFIG_RT_GROUP_SCHEDstruct {int		curr; /* highest queued rt task prio */
#ifdef CONFIG_SMPint		next; /* next highest */
#endif} highest_prio;
#endif
#ifdef CONFIG_SMPunsigned int		rt_nr_migratory;unsigned int		rt_nr_total;int			overloaded;struct plist_head	pushable_tasks;#endif /* CONFIG_SMP */int			rt_queued;int			rt_throttled;u64			rt_time;u64			rt_runtime;/* Nests inside the rq lock: */raw_spinlock_t		rt_runtime_lock;#ifdef CONFIG_RT_GROUP_SCHEDunsigned int		rt_nr_boosted;struct rq		*rq;struct task_group	*tg;
#endif
};/* Deadline class' related fields in a runqueue */
struct dl_rq {/* runqueue is an rbtree, ordered by deadline */struct rb_root_cached	root;unsigned int		dl_nr_running;#ifdef CONFIG_SMP/** Deadline values of the currently executing and the* earliest ready task on this rq. Caching these facilitates* the decision whether or not a ready but not running task* should migrate somewhere else.*/struct {u64		curr;u64		next;} earliest_dl;unsigned int		dl_nr_migratory;int			overloaded;/** Tasks on this rq that can be pushed away. They are kept in* an rb-tree, ordered by tasks' deadlines, with caching* of the leftmost (earliest deadline) element.*/struct rb_root_cached	pushable_dl_tasks_root;
#elsestruct dl_bw		dl_bw;
#endif/** "Active utilization" for this runqueue: increased when a* task wakes up (becomes TASK_RUNNING) and decreased when a* task blocks*/u64			running_bw;/** Utilization of the tasks "assigned" to this runqueue (including* the tasks that are in runqueue and the tasks that executed on this* CPU and blocked). Increased when a task moves to this runqueue, and* decreased when the task moves away (migrates, changes scheduling* policy, or terminates).* This is needed to compute the "inactive utilization" for the* runqueue (inactive utilization = this_bw - running_bw).*/u64			this_bw;u64			extra_bw;/** Maximum available bandwidth for reclaiming by SCHED_FLAG_RECLAIM* tasks of this rq. Used in calculation of reclaimable bandwidth(GRUB).*/u64			max_bw;/** Inverse of the fraction of CPU utilization that can be reclaimed* by the GRUB algorithm.*/u64			bw_ratio;
};struct rq {/* runqueue lock: */raw_spinlock_t		__lock;/** nr_running and cpu_load should be in the same cacheline because* remote CPUs use both these fields when doing load calculation.*/unsigned int		nr_running;
#ifdef CONFIG_NUMA_BALANCINGunsigned int		nr_numa_running;unsigned int		nr_preferred_running;unsigned int		numa_migrate_on;
#endif
#ifdef CONFIG_NO_HZ_COMMON
#ifdef CONFIG_SMPunsigned long		last_blocked_load_update_tick;unsigned int		has_blocked_load;call_single_data_t	nohz_csd;
#endif /* CONFIG_SMP */unsigned int		nohz_tick_stopped;atomic_t		nohz_flags;
#endif /* CONFIG_NO_HZ_COMMON */#ifdef CONFIG_SMPunsigned int		ttwu_pending;
#endifu64			nr_switches;#ifdef CONFIG_UCLAMP_TASK/* Utilization clamp values based on CPU's RUNNABLE tasks */struct uclamp_rq	uclamp[UCLAMP_CNT] ____cacheline_aligned;unsigned int		uclamp_flags;
#define UCLAMP_FLAG_IDLE 0x01
#endifstruct cfs_rq		cfs;struct rt_rq		rt;struct dl_rq		dl;#ifdef CONFIG_FAIR_GROUP_SCHED/* list of leaf cfs_rq on this CPU: */struct list_head	leaf_cfs_rq_list;struct list_head	*tmp_alone_branch;
#endif /* CONFIG_FAIR_GROUP_SCHED *//** This is part of a global counter where only the total sum* over all CPUs matters. A task can increase this counter on* one CPU and if it got migrated afterwards it may decrease* it on another CPU. Always updated under the runqueue lock:*/unsigned int		nr_uninterruptible;struct task_struct __rcu	*curr;struct task_struct	*idle;struct task_struct	*stop;unsigned long		next_balance;struct mm_struct	*prev_mm;unsigned int		clock_update_flags;u64			clock;/* Ensure that all clocks are in the same cache line */u64			clock_task ____cacheline_aligned;u64			clock_pelt;unsigned long		lost_idle_time;atomic_t		nr_iowait;#ifdef CONFIG_SCHED_DEBUGu64 last_seen_need_resched_ns;int ticks_without_resched;
#endif#ifdef CONFIG_MEMBARRIERint membarrier_state;
#endif#ifdef CONFIG_SMPstruct root_domain		*rd;struct sched_domain __rcu	*sd;unsigned long		cpu_capacity;unsigned long		cpu_capacity_orig;struct callback_head	*balance_callback;unsigned char		nohz_idle_balance;unsigned char		idle_balance;unsigned long		misfit_task_load;/* For active balancing */int			active_balance;int			push_cpu;struct cpu_stop_work	active_balance_work;/* CPU of this runqueue: */int			cpu;int			online;struct list_head cfs_tasks;struct sched_avg	avg_rt;struct sched_avg	avg_dl;
#ifdef CONFIG_HAVE_SCHED_AVG_IRQstruct sched_avg	avg_irq;
#endif
#ifdef CONFIG_SCHED_THERMAL_PRESSUREstruct sched_avg	avg_thermal;
#endifu64			idle_stamp;u64			avg_idle;unsigned long		wake_stamp;u64			wake_avg_idle;/* This is used to determine avg_idle's max value */u64			max_idle_balance_cost;#ifdef CONFIG_HOTPLUG_CPUstruct rcuwait		hotplug_wait;
#endif
#endif /* CONFIG_SMP */#ifdef CONFIG_IRQ_TIME_ACCOUNTINGu64			prev_irq_time;
#endif
#ifdef CONFIG_PARAVIRTu64			prev_steal_time;
#endif
#ifdef CONFIG_PARAVIRT_TIME_ACCOUNTINGu64			prev_steal_time_rq;
#endif/* calc_load related fields */unsigned long		calc_load_update;long			calc_load_active;#ifdef CONFIG_SCHED_HRTICK
#ifdef CONFIG_SMPcall_single_data_t	hrtick_csd;
#endifstruct hrtimer		hrtick_timer;ktime_t 		hrtick_time;
#endif#ifdef CONFIG_SCHEDSTATS/* latency stats */struct sched_info	rq_sched_info;unsigned long long	rq_cpu_time;/* could above be rq->cfs_rq.exec_clock + rq->rt_rq.rt_runtime ? *//* sys_sched_yield() stats */unsigned int		yld_count;/* schedule() stats */unsigned int		sched_count;unsigned int		sched_goidle;/* try_to_wake_up() stats */unsigned int		ttwu_count;unsigned int		ttwu_local;
#endif#ifdef CONFIG_CPU_IDLE/* Must be inspected within a rcu lock section */struct cpuidle_state	*idle_state;
#endif#ifdef CONFIG_SMPunsigned int		nr_pinned;
#endifunsigned int		push_busy;struct cpu_stop_work	push_work;#ifdef CONFIG_SCHED_CORE/* per rq */struct rq		*core;struct task_struct	*core_pick;unsigned int		core_enabled;unsigned int		core_sched_seq;struct rb_root		core_tree;/* shared state -- careful with sched_core_cpu_deactivate() */unsigned int		core_task_seq;unsigned int		core_pick_seq;unsigned long		core_cookie;unsigned int		core_forceidle_count;unsigned int		core_forceidle_seq;unsigned int		core_forceidle_occupation;u64			core_forceidle_start;
#endif
};// runqueues (not export symbol)
struct rq* _prq = NULL;struct rq* my_cpu_rq(int i_cpu)
{return per_cpu_ptr(_prq, i_cpu);
}u64 my_rq_clock_task(void)
{struct rq* prq = my_cpu_rq(smp_processor_id());return prq->clock_task;
}#define TESTDIOMONITOR_FILE_MAXLEN  1024typedef struct testdiomonitor_sample {struct timespec64 time;int cpu;int pid;int tgid;int ppid;char comm[TASK_COMM_LEN];char ppidcomm[TASK_COMM_LEN];// 0 or 1int bin_iowait;/** "swDstart" // 在sched_switch里* "waDstop"  // 在sched_waking里* "swDiostart" // 在sched_switch里* "waDiostop"  // 在sched_waking里* "Dexceed"    // 超出阈值，非iowait* "Dioexceed"  // 超出阈值，iowait*/const char* desc;u64 dtimens;    // 纳秒单位，D状态持续的时间u64 iowaittimens;   // 纳秒单位，等待io的时间int stackn;void* parray_stack[TEST_STACK_TRACE_ENTRIES];int wakercpu;int wakerpid;int wakertgid;int wakerppid;char wakercomm[TASK_COMM_LEN];char wakerppidcomm[TASK_COMM_LEN];int wakerstackn;void* parray_wakerstack[TEST_STACK_TRACE_ENTRIES];u32 writedone;  // 0 or 1
} testdiomonitor_sample;#define TESTDIOMONITOR_SAMPLE_RINGBUFF_MAXCOUNT  8192typedef struct testdiomonitor_sample_ringbuff {testdiomonitor_sample* parray_sample;volatile u64 wp;    // Index is wp & (TESTDIOMONITOR_SAMPLE_RINGBUFF_MAXCOUNT - 1).volatile u64 rp;    // Index is rp & (TESTDIOMONITOR_SAMPLE_RINGBUFF_MAXCOUNT - 1).u32 skipcount;  // 0 means no skip any abnormal event
} testdiomonitor_sample_ringbuff;#define TESTDIOMONITOR_LINEBUFF  1024typedef struct testdiomonitor_env {struct file* file;char file_linebuff[TESTDIOMONITOR_LINEBUFF];int headoffset;loff_t file_pos;testdiomonitor_sample_ringbuff ringbuff;
} testdiomonitor_env;static testdiomonitor_env _env;static struct delayed_work work_write_file;
static struct workqueue_struct *wq_write_file;#define FILENAME        "test_new.txt"void init_file(void)
{_env.file = filp_open(FILENAME, O_WRONLY | O_CREAT | O_TRUNC, 0644);if (IS_ERR(_env.file)) {_env.file = NULL;}
}void exit_file(void)
{if (_env.file) {filp_close(_env.file, NULL);}
}void testdiomonitor_write_file(char* i_pchar, int i_size)
{if (_env.file) {kernel_write(_env.file, i_pchar, i_size, &_env.file_pos);}
}void testdiomonitor_write_file_emptyline(void)
{testdiomonitor_write_file("\n", strlen("\n"));
}void testdiomonitor_file_oneline(const char* i_format, ...)
{char* pcontent = &_env.file_linebuff[_env.headoffset];va_list args;va_start(args, i_format);vsnprintf(pcontent, TESTDIOMONITOR_LINEBUFF - _env.headoffset, i_format, args);va_end(args);testdiomonitor_write_file(_env.file_linebuff, strlen(_env.file_linebuff));
}void testdiomonitor_replace_null_with_space(char *str, int n) {for (int i = 0; i < n - 1; i++) {if (str[i] == '\0') {str[i] = ' ';}}
}void testdiomonitor_set_cmdline(char* i_pbuff, int i_buffsize, struct task_struct* i_ptask)
{int ret = _get_cmdline_func(i_ptask, i_pbuff, i_buffsize);if (ret <= 0) {i_pbuff[0] = '\0';return;}testdiomonitor_replace_null_with_space(i_pbuff, ret);i_pbuff[ret - 1] = '\0';
}void testdiomonitor_checkget_parentinfo_and_cmdline(testdiomonitor_sample* io_psample, struct task_struct* i_ptask)
{struct task_struct* parent;rcu_read_lock();parent = rcu_dereference(i_ptask->real_parent);io_psample->ppid = parent->pid;strlcpy(io_psample->ppidcomm, parent->comm, TASK_COMM_LEN);rcu_read_unlock();
}void testdiomonitor_checkget_parentinfo_and_cmdline_waker(testdiomonitor_sample* io_psample, struct task_struct* i_ptask)
{struct task_struct* parent;rcu_read_lock();parent = rcu_dereference(i_ptask->real_parent);io_psample->wakerppid = parent->pid;strlcpy(io_psample->wakerppidcomm, parent->comm, TASK_COMM_LEN);rcu_read_unlock();
}#define TESTDIOMONITOR_COMMANDLINE_MAX 128static void write_file(struct work_struct *w)
{ssize_t ret;u32 index;testdiomonitor_sample* psample;struct tm t;char timestr[64];char exceedstr[64];char temp_commandline[TESTDIOMONITOR_COMMANDLINE_MAX];struct pid* pid_struct;struct task_struct* ptask;int stacki;while (_env.ringbuff.rp != _env.ringbuff.wp) {index = (_env.ringbuff.rp & (TESTDIOMONITOR_SAMPLE_RINGBUFF_MAXCOUNT - 1));psample = &_env.ringbuff.parray_sample[index];if (psample->writedone != 1) {break;}testdiomonitor_write_file_emptyline();_env.headoffset = sprintf(_env.file_linebuff, "[%llu][%s] ", _env.ringbuff.rp, psample->desc);time64_to_tm(psample->time.tv_sec + 8 * 60 * 60, 0, &t);snprintf(timestr, 64, "%04ld-%02d-%02d-%02d_%02d_%02d.%09ld",1900 + t.tm_year, t.tm_mon + 1, t.tm_mday, t.tm_hour, t.tm_min, t.tm_sec, psample->time.tv_nsec);if (psample->desc == TESTDIOMONITOR_SAMPLEDESC_DEXCEED) {snprintf(exceedstr, 64, "dtimens[%llu]", psample->dtimens);}else if (psample->desc == TESTDIOMONITOR_SAMPLEDESC_DIOEXCEED) {snprintf(exceedstr, 64, "iowaittimens[%llu]", psample->iowaittimens);}else if (psample->desc == TESTDIOMONITOR_SAMPLEDESC_IOEXCEED) {snprintf(exceedstr, 64, "delayacct_iowaittimens[%llu]", psample->iowaittimens);}else {exceedstr[0] = '\0';}if (psample->desc == TESTDIOMONITOR_SAMPLEDESC_DIOEXCEED) {testdiomonitor_file_oneline("begin...time[%s]wakercpu[%d]desc[%s]%s\n", timestr, psample->wakercpu, psample->desc, "wakerDioexceed");testdiomonitor_file_oneline("wakertgid[%d]wakerpid[%d]wakercomm[%s]wakerppid[%d]wakerppidcomm[%s]\n",psample->wakertgid, psample->wakerpid, psample->wakercomm, psample->wakerppid, psample->wakerppidcomm);pid_struct = find_get_pid(psample->wakerpid);if (pid_struct) {ptask = get_pid_task(pid_struct, PIDTYPE_PID);if (ptask) {testdiomonitor_set_cmdline(temp_commandline, TESTDIOMONITOR_COMMANDLINE_MAX, ptask);put_task_struct(ptask);}else {temp_commandline[0] = '\0';}put_pid(pid_struct);}else {temp_commandline[0] = '\0';}testdiomonitor_file_oneline("wakercommandline[%s]\n", temp_commandline);pid_struct = find_get_pid(psample->wakerppid);if (pid_struct) {ptask = get_pid_task(pid_struct, PIDTYPE_PID);if (ptask) {testdiomonitor_set_cmdline(temp_commandline, TESTDIOMONITOR_COMMANDLINE_MAX, ptask);put_task_struct(ptask);}else {temp_commandline[0] = '\0';}put_pid(pid_struct);}else {temp_commandline[0] = '\0';}testdiomonitor_file_oneline("wakerppid_commandline[%s]\n", temp_commandline);testdiomonitor_file_oneline("stack[%d]:\n", psample->wakerstackn);for (stacki = 0; stacki < psample->wakerstackn; stacki++) {testdiomonitor_file_oneline("%*c%pS\n", 5, ' ', (void *)psample->parray_wakerstack[stacki]);}testdiomonitor_file_oneline("cpu[%d]desc[%s]%s\n", psample->cpu, psample->desc, exceedstr);}else {testdiomonitor_file_oneline("begin...time[%s]cpu[%d]desc[%s]%s\n", timestr, psample->cpu, psample->desc, exceedstr);}testdiomonitor_file_oneline("tgid[%d]pid[%d]comm[%s]ppid[%d]ppidcomm[%s]\n",psample->tgid, psample->pid, psample->ppidcomm, psample->ppid, psample->ppidcomm);pid_struct = find_get_pid(psample->pid);if (pid_struct) {ptask = get_pid_task(pid_struct, PIDTYPE_PID);if (ptask) {testdiomonitor_set_cmdline(temp_commandline, TESTDIOMONITOR_COMMANDLINE_MAX, ptask);put_task_struct(ptask);}else {temp_commandline[0] = '\0';}put_pid(pid_struct);}else {temp_commandline[0] = '\0';}testdiomonitor_file_oneline("commandline[%s]\n", temp_commandline);pid_struct = find_get_pid(psample->ppid);if (pid_struct) {ptask = get_pid_task(pid_struct, PIDTYPE_PID);if (ptask) {testdiomonitor_set_cmdline(temp_commandline, TESTDIOMONITOR_COMMANDLINE_MAX, ptask);put_task_struct(ptask);}else {temp_commandline[0] = '\0';}put_pid(pid_struct);}else {temp_commandline[0] = '\0';}testdiomonitor_file_oneline("ppid_commandline[%s]\n", temp_commandline);testdiomonitor_file_oneline("stack[%d]:\n", psample->stackn);for (stacki = 0; stacki < psample->stackn; stacki++) {testdiomonitor_file_oneline("%*c%pS\n", 5, ' ', (void *)psample->parray_stack[stacki]);}testdiomonitor_write_file_emptyline();psample->writedone = 0;_env.ringbuff.rp ++;}queue_delayed_work_on(nr_cpu_ids - 1, wq_write_file,&work_write_file, 1);
}static void init_write_file(void)
{init_file();wq_write_file = alloc_workqueue("testdiomonitor_write_file", WQ_MEM_RECLAIM, 0);INIT_DELAYED_WORK(&work_write_file, write_file);queue_delayed_work_on(nr_cpu_ids - 1, wq_write_file,&work_write_file, 3);
}static void exit_write_file(void)
{cancel_delayed_work_sync(&work_write_file);destroy_workqueue(wq_write_file);exit_file();
}void init_testdiomonitor_sample_ringbuff(void) 
{testdiomonitor_sample* psample;_env.ringbuff.parray_sample = kvzalloc(sizeof(testdiomonitor_sample) * TESTDIOMONITOR_SAMPLE_RINGBUFF_MAXCOUNT, GFP_KERNEL);
}void exit_testdiomonitor_sample_ringbuff(void)
{kvfree(_env.ringbuff.parray_sample);
}testdiomonitor_sample* testdiomonitor_get_psample(void)
{u64 windex_raw, windex_raw_old;u32 windex;while (1) {windex_raw = _env.ringbuff.wp;if (windex_raw - _env.ringbuff.rp >= (u64)(TESTDIOMONITOR_SAMPLE_RINGBUFF_MAXCOUNT)) {_env.ringbuff.skipcount ++;return NULL;}// atomic_cmpxchg return old valuewindex_raw_old = atomic64_cmpxchg((atomic64_t*)&_env.ringbuff.wp,windex_raw, windex_raw + 1);if (windex_raw_old == windex_raw) {break;}}windex = (u32)(windex_raw & (u64)(TESTDIOMONITOR_SAMPLE_RINGBUFF_MAXCOUNT - 1));return &_env.ringbuff.parray_sample[windex];
}void testdiomonitor_add_sample(const char* i_desc, struct task_struct* i_task, u64 i_timens)
{testdiomonitor_sample* psample = testdiomonitor_get_psample();if (!psample) {return;}ktime_get_real_ts64(&psample->time);psample->cpu = task_cpu(i_task);psample->pid = i_task->pid;psample->tgid = i_task->tgid;strlcpy(psample->comm, i_task->comm, TASK_COMM_LEN);testdiomonitor_checkget_parentinfo_and_cmdline(psample, i_task);psample->bin_iowait = i_task->in_iowait;psample->desc = i_desc;if (i_desc == TESTDIOMONITOR_SAMPLEDESC_DEXCEED) {psample->dtimens = i_timens;}else if (i_desc == TESTDIOMONITOR_SAMPLEDESC_DIOEXCEED || i_desc == TESTDIOMONITOR_SAMPLEDESC_IOEXCEED) {psample->iowaittimens = i_timens;}psample->stackn = _stack_trace_save_tsk(i_task, (unsigned long*)psample->parray_stack, TEST_STACK_TRACE_ENTRIES, 0);if (i_desc == TESTDIOMONITOR_SAMPLEDESC_DIOEXCEED) {psample->wakercpu = smp_processor_id();psample->wakerpid = current->pid;psample->wakertgid = current->tgid;strlcpy(psample->wakercomm, current->comm, TASK_COMM_LEN);testdiomonitor_checkget_parentinfo_and_cmdline_waker(psample, current);psample->wakerstackn = _stack_trace_save_tsk(current, (unsigned long*)psample->parray_wakerstack, TEST_STACK_TRACE_ENTRIES, 0);}psample->writedone = 1;
}static void cb_sched_switch(void *i_data, bool i_preempt,struct task_struct *i_prev,struct task_struct *i_next,unsigned int i_prev_state)
{
#ifndef TESTDIOMONITOR_SIMPLEvoid* parray_stack[TEST_STACK_TRACE_ENTRIES];int num_stack;int stacki;if (i_prev_state == TASK_UNINTERRUPTIBLE) {if (i_prev->in_iowait) {testdiomonitor_add_sample(TESTDIOMONITOR_SAMPLEDESC_SWDIOSTART, i_prev, 0);}else {testdiomonitor_add_sample(TESTDIOMONITOR_SAMPLEDESC_SWDSTART, i_prev, 0);}}else if (i_prev->in_iowait) {testdiomonitor_add_sample(TESTDIOMONITOR_SAMPLEDESC_SWDIOSTART, i_prev, 0);}
#endif
}const char* getstatstr_bystate(u32 i_state) {switch (i_state) {case TASK_RUNNING:return "TASK_RUNNING";case TASK_INTERRUPTIBLE:return "TASK_INTERRUPTIBLE";case TASK_UNINTERRUPTIBLE:return "TASK_UNINTERRUPTIBLE";default:return "other";}
}static void cb_sched_waking(void *i_data, struct task_struct *i_p) {if (i_p->__state == TASK_UNINTERRUPTIBLE) {//u64 currns = my_rq_clock_task();struct rq* prq = my_cpu_rq(task_cpu(i_p));u64 currns = prq->clock_task;u64 local_c = local_clock();int cpuid = smp_processor_id();if (i_p->in_iowait) {
#ifndef TESTDIOMONITOR_SIMPLEtestdiomonitor_add_sample(TESTDIOMONITOR_SAMPLEDESC_WADIOSTOP, i_p, 0);
#endif
#ifdef TESTDIOMONITOR_SIMPLEif (currns - i_p->se.exec_start >= TESTDIOMONITOR_SIMPLE_THRESHOLDNS)
#endiftestdiomonitor_add_sample(TESTDIOMONITOR_SAMPLEDESC_DIOEXCEED, i_p, currns - i_p->se.exec_start);
#ifndef TESTDIOMONITOR_SIMPLEif (i_p->se.exec_start > currns) {//if (task_cpu(i_p) == cpuid) {printk("comm[%s]pid[%d]exec_start[%llu]currns[%llu]local_clock[%llu]last_cpu[%d]cpuid[%d]\n", i_p->comm, i_p->pid, i_p->se.exec_start, currns, local_c, task_cpu(i_p), cpuid);}}// if (printk_ratelimit()) {//     printk("waking dump_stack[D]:\n");//     dump_stack();// }
#endif}
#ifndef TESTDIOMONITOR_SIMPLEelse {testdiomonitor_add_sample(TESTDIOMONITOR_SAMPLEDESC_WADSTOP, i_p, 0);testdiomonitor_add_sample(TESTDIOMONITOR_SAMPLEDESC_DEXCEED, i_p, my_rq_clock_task() - i_p->se.exec_start);if (i_p->se.exec_start > currns) {//if (task_cpu(i_p) == cpuid) {printk("comm[%s]pid[%d]exec_start[%llu]currns[%llu]local_clock[%llu]last_cpu[%d]cpuid[%d]\n", i_p->comm, i_p->pid, i_p->se.exec_start, currns, local_c, task_cpu(i_p), cpuid);}}}
#endif}else if (i_p->in_iowait) {struct rq* prq = my_cpu_rq(task_cpu(i_p));u64 currns = prq->clock_task;u64 local_c = local_clock();int cpuid = smp_processor_id();//if (printk_ratelimit()) // {//     printk("i_p->__state=[%u][%s]\n", i_p->__state, getstatstr_bystate(i_p->__state));//     printk("waking dump_stack[K]:\n");//     dump_stack();// }
#ifndef TESTDIOMONITOR_SIMPLEtestdiomonitor_add_sample(TESTDIOMONITOR_SAMPLEDESC_WADIOSTOP, i_p, 0);
#endif
#ifdef TESTDIOMONITOR_SIMPLEif (currns - i_p->se.exec_start >= TESTDIOMONITOR_SIMPLE_THRESHOLDNS)
#endiftestdiomonitor_add_sample(TESTDIOMONITOR_SAMPLEDESC_DIOEXCEED, i_p, currns - i_p->se.exec_start);}
}static void cb_iodelay_account(void *i_data, struct task_struct *i_curr,unsigned long long i_delta)
{
#ifdef TESTDIOMONITOR_SIMPLEif (i_delta >= TESTDIOMONITOR_SIMPLE_THRESHOLDNS)
#endiftestdiomonitor_add_sample(TESTDIOMONITOR_SAMPLEDESC_IOEXCEED, i_curr, i_delta);
}struct kern_tracepoint {void *callback;struct tracepoint *ptr;bool bregister;
};
static void clear_kern_tracepoint(struct kern_tracepoint *tp)
{if (tp->bregister) {tracepoint_probe_unregister(tp->ptr, tp->callback, NULL);}
}#define INIT_KERN_TRACEPOINT(tracepoint_name) \static struct kern_tracepoint mykern_##tracepoint_name = {.callback = NULL, .ptr = NULL, .bregister = false};#define TRACEPOINT_CHECK_AND_SET(tracepoint_name)                                             \static void tracepoint_name##_tracepoint_check_and_set(struct tracepoint *tp, void *priv) \{                                                                                \if (!strcmp(#tracepoint_name, tp->name))                                     \{                                                                            \((struct kern_tracepoint *)priv)->ptr = tp;                          \return;                                                                  \}                                                                            \}INIT_KERN_TRACEPOINT(sched_switch)
TRACEPOINT_CHECK_AND_SET(sched_switch)
INIT_KERN_TRACEPOINT(sched_waking)
TRACEPOINT_CHECK_AND_SET(sched_waking)
#ifdef IODELAY_TRACEPOINT_ENABLE
INIT_KERN_TRACEPOINT(iodelay_account)
TRACEPOINT_CHECK_AND_SET(iodelay_account)
#endiftypedef unsigned long (*kallsyms_lookup_name_func)(const char *name);
kallsyms_lookup_name_func _kallsyms_lookup_name_func;void* get_func_by_symbol_name_kallsyms_lookup_name(void)
{int ret;void* pfunc = NULL;struct kprobe kp;memset(&kp, 0, sizeof(kp));kp.symbol_name = "kallsyms_lookup_name";kp.pre_handler = NULL;kp.addr = NULL;	// 作为强调，提示使用symbol_nameret = register_kprobe(&kp);if (ret < 0) {printk("register_kprobe fail!\n");return NULL;}printk("register_kprobe succeed!\n");pfunc = (void*)kp.addr;unregister_kprobe(&kp);return pfunc;
}void* get_func_by_symbol_name(const char* i_symbol)
{if (_kallsyms_lookup_name_func == NULL) {return NULL;}return _kallsyms_lookup_name_func(i_symbol);
}static int __init testdiomonitor_init(void)
{//printk("offset of mmap_lock in mm_struct [%d]\n", offsetof(struct mm_struct, mmap_lock));_kallsyms_lookup_name_func = get_func_by_symbol_name_kallsyms_lookup_name();_prq = get_func_by_symbol_name("runqueues");if (_prq == NULL) {printk(KERN_ERR "get_func_by_symbol_name runqueues failed!\n");return -1;}init_testdiomonitor_sample_ringbuff();init_write_file();_stack_trace_save_tsk = get_func_by_symbol_name("stack_trace_save_tsk");if (_stack_trace_save_tsk == NULL) {printk(KERN_ERR "get_func_by_symbol_name stack_trace_save_tsk failed!\n");return -1;}_get_cmdline_func = get_func_by_symbol_name("get_cmdline");if (_get_cmdline_func == NULL) {printk(KERN_ERR "get_func_by_symbol_name get_cmdline failed!\n");return -1;}mykern_sched_switch.callback = cb_sched_switch;for_each_kernel_tracepoint(sched_switch_tracepoint_check_and_set, &mykern_sched_switch);if (!mykern_sched_switch.ptr) {printk(KERN_ERR "mykern_sched_switch register failed!\n");return -1;}else {printk(KERN_INFO "mykern_sched_switch register succeeded!\n");}tracepoint_probe_register(mykern_sched_switch.ptr, mykern_sched_switch.callback, NULL);mykern_sched_switch.bregister = 1;mykern_sched_waking.callback = cb_sched_waking;for_each_kernel_tracepoint(sched_waking_tracepoint_check_and_set, &mykern_sched_waking);if (!mykern_sched_waking.ptr) {printk(KERN_ERR "mykern_sched_waking register failed!\n");return -1;}else {printk(KERN_INFO "mykern_sched_waking register succeeded!\n");}tracepoint_probe_register(mykern_sched_waking.ptr, mykern_sched_waking.callback, NULL);mykern_sched_waking.bregister = 1;#ifdef IODELAY_TRACEPOINT_ENABLEmykern_iodelay_account.callback = cb_iodelay_account;for_each_kernel_tracepoint(iodelay_account_tracepoint_check_and_set, &mykern_iodelay_account);if (!mykern_iodelay_account.ptr) {printk(KERN_ERR "mykern_iodelay_account register failed!\n");return -1;}else {printk(KERN_INFO "mykern_iodelay_account register succeeded!\n");}tracepoint_probe_register(mykern_iodelay_account.ptr, mykern_iodelay_account.callback, NULL);mykern_iodelay_account.bregister = 1;
#endifreturn 0;
}static void __exit testdiomonitor_exit(void)
{clear_kern_tracepoint(&mykern_sched_switch);clear_kern_tracepoint(&mykern_sched_waking);
#ifdef IODELAY_TRACEPOINT_ENABLEclear_kern_tracepoint(&mykern_iodelay_account);
#endiftracepoint_synchronize_unregister();exit_write_file();exit_testdiomonitor_sample_ringbuff();
}module_init(testdiomonitor_init);
module_exit(testdiomonitor_exit);

2.2 修改部分里的waker相关部分说明

这次的改动是增加了针对进程iodelay唤醒时场景下，除了打印发生iodelay进程的相关堆栈，也打印出waker的堆栈的记录，提示是在哪里的逻辑进行的唤醒。

首先，在testdiomonitor_sample结构体里增加waker相关的部分：

然后，响应的增加waker相关的函数：

在落盘时，如果是TESTDIOMONITOR_SAMPLEDESC_DIOEXCEED类型，也就是iodelay唤醒相关类型时，就补充打印waker的堆栈如下：

也打印出waker的commandline及waker的parent的commandline：

然后在testdiomonitor_add_sample进行采样记录时，判断如果是TESTDIOMONITOR_SAMPLEDESC_DIOEXCEED的场景时进行waker的相关记录：

2.3 修改部分里的为了应对in_iowait状态下的非TASK_UNINTERRUPTIBLE状态

在调试时发现，如果我们只筛选TASK_UNINTERRUPTIBLE状态才做waking的相关sample的记录的话，那么会漏掉filemap的缺页异常场景的sample记录。因为filemap缺页异常场景的进程的状态不是TASK_UNINTERRUPTIBLE状态，而是多了一个bit位，是TASK_KILLABLE状态：

看TASK_KILLABLE状态的定义：

所以，修改了cb_sched_waking里的逻辑，补了一个else判断，如下图：

2.4 运行结果

insmod ko之后，抓到的某一个唤醒iowait的任务的waker和wakee的堆栈截图如下：

上图里由于用的rq_clock来算的iowaittimens，所以可能是有一点误差的但是至少能保证时间轴的单调性，即不会出现算出来的iowaittimens小于0，细节参考之前的博客 在计算进程D状态持续时间及等IO的时间遇到的一处问题-CSDN博客 。

上图的这次就是缺页异常导致的iowait，我们在下面第三章里详细展开分析这个原理。

三、缺页异常导致iowait的原理分析

我们回到上面 2.3 里展示的抓到这一次waker和wakee的堆栈截图：

解释一下，是进程231797这个bash /usr/local/sunlogin/etc/watch.sh的脚本进程里执行了grep -v /usr/local/sunlogin/etc/watch.sh（进程231801）在执行时，读一个文件时，使用了pagecache，发生了缺页异常，在等io完成相关page的加载时（io把相关文件从磁盘读回到page cache），这时候，231797这个bash /usr/local/sunlogin/etc/watch.sh的脚本进程又执行了grep sunloginclient --mod=service脚本（进程231799），进程231799在读一个文件时，发现这个文件的pagecache的页对应的folio被置上了PG_locked，说明正在读磁盘等磁盘完成读请求，所以进程231799陷入了D状态的睡眠（in_iowait被置上）；然后，进程231801被通知完成了读之后，也唤醒了其他要读该folio的进程，这里唤醒的是231799进程。

要注意，读磁盘读的可能是数据文件，也可能是程序本身，也可能是so库，等等。

3.1 抓到的filemap_fault全部是filemap_fault+0xe8这个offset

我们看一下抓到的所有的filemap_fault，这次抓到总共88次：

每次都是filemap_fault的0xe8这个offset，继而调用到folio_wait_bit_common的0x124这个offset都是88次：

每次都是调用到了folio_wait_bit_common的0x124的位置：

3.2 确定相关的调用链

在看vmlinux里找对应源码前，我们先确认一下我们看的vmlinux是否匹配：

对应的vmlinux里filemap_fault函数的首地址ffffffff8137ac20加上0xab0：

就是下一个函数的开头：

所以是匹配的。

我们找一下filemap_fault里的0xe8的位置：

ffffffff8137ac20加上0xe8是FFFFFFFF8137AD08：

搜一下这个call对应的原始代码：

return folio_wait_bit_common(folio, PG_locked, TASK_KILLABLE,

代码里就一处是：

由于堆栈里没有__folio_lock_killable，所以说明__folio_lock_killable被弄成了inline方式被使用，看__folio_lock_killable的就两个引用的地方，一个是__folio_lock_or_retry调用了__folio_lock_killable，如下图：

还有一个是lock_folio_maybe_drop_mmap调用了__folio_lock_killable：

稍加比较就可以得出是上面的第二处即lock_folio_maybe_drop_mmap调用的__folio_lock_killable。

所以，我们iowait相关的缺页异常的这个调用链是：

filemap_fault->lock_folio_maybe_drop_mmap->__folio_lock_killable->folio_wait_bit_common

3.3 关于PG_locked标志位

在明确了调用链后，我们回过来看一下这个__folio_lock_killable这个函数：

它的意思是等一个folio的PG_locked的标志位被释放，在等的期间，进程被设置成TASK_KILLABLE状态，而TASK_KILLABLE状态在上面 2.3 里也说过，是多了TASK_WAKEKILL的这个标志位的。

为什么内核里有这么一个设计，置上了PG_locked来等io，等io完成再清除这个标志位，其他人在这个期间要等待，为什么要有这么个设计？

其实很容易理解，第一个在读相关文件发生缺页异常，并下发io读请求，等待io完成这个期间，如果在io完成之前就放开让其他缺页异常进来，那么读到的内容就会是错误的或者不完整的内容。