Re: Possible bug in putting processes to sleep

[Lasse Bigum <zenith at cs dot aau dot dk>]

Oops, forgot the most important info.

This is with the systemtap-20070303 snapshot, running on a 2.6.20 kernel
on Gentoo.

/Lasse

On 11:42, Tue 13 Mar, Lasse Bigum wrote:
> Hi,
> 
> I wanted to file a bug report on this, but I think the registration mail
> got caught up in the greylisting for now.
> 
> I have a small script that detects if a process with a specific name is
> running, and if so, puts it to sleep straight away after detecting a
> system call from it.
> 
> # cat stap_app.stp
> %{
> #include <linux/signal.h>
> %}
> 
> global countdown, p_id
> 
> function do_sleep:long (process_id:long)
> %{
>     struct task_struct *sigtask;
>     sigtask = find_task_by_pid(THIS->process_id);
>     send_sig(SIGSTOP, sigtask, 0);
> 
>     printk("SOV\n");
> %}
> 
> probe kernel.function("sys_*") {
>     if (execname() == "open-close") {
>         printf("%s\n", probefunc());
> 
>         do_sleep(pid());
>     }
> }
> 
> Next, I run a small program that can read from a file, or write to it, or print out some info about how to use it.
> 
> The code is as follows:
> # cat open-close.c
> #include <stdlib.h>
> #include <stdio.h>
> #include <string.h>
> 
> int main(int argc, char *argv[])
> {
>         char *userinput = malloc(20);
>         FILE *file;
>         char text[100];
> 
>         if (argc < 2) {
>                 printf("usage: 1 for reading, 2 'text' for writing 'text' \n");
>                 exit(1);
>         }
> 
>         if (strcmp(argv[1],"1") == 0) {
>                 file = fopen("test", "r");
> 
>                 fgets(text,100,file);
>                 printf("LÃst = %s\n", text);
> 
>                 fclose(file);
>         } else if (strcmp(argv[1],"2") == 0) {
>                 file = fopen("test", "w");
> 
>                 strcpy(userinput, argv[2]);
>                 fprintf(file, "%s", userinput);
>                 printf("skrevet: %s\n", userinput);
> 
>                 fclose(file);
>         } else {
>                 printf("usage: 1 for reading, 2 'text' for writing 'text'.. \n");
>                 exit(1);
>         }
> 
>         return 0;
> }
> 
> When I run the stap script, and I subsequently run the program, I get
> this:
> # staprun /root/.systemtap/cache/af/stap_aff2f447749d27fd4480a10ee9a53dc8_47299.ko
> sys_close
> sys_close
> 
> -----
> 
> Now for the actual question: any explanation of why two system calls are
> being printed out?
> 
> Shouldn't the program be halted right after the first system call is
> made?
> 
> /Lasse

Attachment: smime.p7s
Description: S/MIME cryptographic signature