linux内核中的信号机制--信号发送

1. GAINwhenlowonmemorywejust
2. makesureatleastonesignalgetsdeliveredanddont
3. passontheinfostruct.*/
5. q=__sigqueue_alloc(t,GFP_ATOMIC,(sig
6. ((unsignedlong)info<2||
7. info->si_code>=0)));//分配sigqueue结构
8. if(q){//如果成功分配到sigqueue结构，就把它添加到队列中，并对其初始化
9. list_add_tail(&q->list,&signals->list);
10. switch((unsignedlong)info){
11. case0:
12. q->info.si_signo=sig;
13. q->info.si_errno=0;
14. q->info.si_code=SI_USER;
15. q->info.si_pid=current->pid;
16. q->info.si_uid=current->uid;
17. break;
18. case1:
19. q->info.si_signo=sig;
20. q->info.si_errno=0;
21. q->info.si_code=SI_KERNEL;
22. q->info.si_pid=0;
23. q->info.si_uid=0;
24. break;
25. default:
26. copy_siginfo(&q->info,info);//拷贝sigqueue结构
27. break;
28. }
29. }else{
30. if(sig>=SIGRTMIN&&info&&(unsignedlong)info!=1
31. &&info->si_code!=SI_USER)
32. /*
33. *Queueoverflow,abort.Wemayabortifthesignalwasrt
34. *andsentbyuserusingsomethingotherthankill().
35. */
36. return-EAGAIN;
37. if(((unsignedlong)info>1)&&(info->si_code==SI_TIMER))
38. /*
39. *Setupareturntoindicatethatwedropped
40. *thesignal.
41. */
42. ret=info->si_sys_private;
43. }
45. out_set:
46. sigaddset(&signals->signal,sig);//设置信号位图
47. returnret;
48. }

从上面的分析可以看出，我们看到信号被添加到信号队列之后，会调用signal_wake_up()唤醒这个进程，signal_wake_up()(kernel/signal.c)的定义如下：

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1. /*
2. *Tellaprocessthatithasanewactivesignal..
3. *
4. *NOTE!werelyonthepreviousspin_lockto
5. *lockinterruptsforus!Wecanonlybecalledwith
6. *"siglock"held,andthelocalinterruptmust
7. *havebeendisabledwhenthatgotacquired!
8. *
9. *Noneedtosetneed_reschedsincesignaleventpassing
10. *goesthrough->blocked
11. */
12. voidsignal_wake_up(structtask_struct*t,intresume)
13. {
14. unsignedintmask;
16. set_tsk_thread_flag(t,TIF_SIGPENDING);//为进程设置TIF_SIGPENDING标志
18. /*
19. *ForSIGKILL,wewanttowakeitupinthestopped/tracedcase.
20. *Wedontcheckt->stateherebecausethereisaracewithit
21. *executinganotherprocessorandjustnowenteringstoppedstate.
22. *Byusingwake_up_state,weensuretheprocesswillwakeupand
23. *handleitsdeathsignal.
24. */
25. mask=TASK_INTERRUPTIBLE;
26. if(resume)
27. mask|=TASK_STOPPED|TASK_TRACED;
28. if(!wake_up_state(t,mask))
29. kick_process(t);
30. }

signal_wake_up()首先为进程设置TIF_SIGPENDING标志，说明该进程有延迟的信号要等待处理。然后再调用wake_up_state()唤醒目标进程，如果目标进程在其他的CPU上运行，wake_up_state()将返回0，此时调用kick_process()向该CPU发送一个处理器间中断。当中断返回前戏，会为当前进程处理延迟的信号。

此后当该进程被调度时，在进程返回用户空间前，会调用do_notify_resume()处理该进程的信号。