[RFC] a question about stack size form /proc/pid/task/child pid/limits

[RFC] a question about stack size form /proc/pid/task/child pid/limits

[Xishi Qiu]

Hi, I find if I use a defined stack size to create a child thread,
then the max stack size from /proc/pid/task/child pid/limits still
shows "Max stack size            8388608", it doesn't update to
the user defined size, is it a problem?

Here is the test code:
		...
                pthread_attr_t attr;
                ret = pthread_attr_init(&attr);
                if (ret)
                        printf("error\n");
                ret = pthread_attr_setstacksize(&attr, 83886080);
                if (ret)
                        printf("error\n");
                ret = pthread_create(&id_1[i], &attr, (void  *)thread_alloc, NULL);
		...

I use strace to track the app, it shows glibc will call mmap to
alloc the child thread stack. So should gilbc call setrlimit to
update the stack limit too?

And glibc will only insert a guard at the start of the stack vma,
so the stack vma maybe merged to another vma at the end, right?

...
mmap(NULL, 83890176, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_STACK, -1, 0) = 0x7fca1d6a6000
mprotect(0x7fca1d6a6000, 4096, PROT_NONE) = 0
clone(child_stack=0x7fca226a5fb0, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID, parent_tidptr=0x7fca226a69d0, tls=0x7fca226a6700, child_tidptr=0x7fca226a69d0) = 21043
...

Thanks,
Xishi Qiu

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Re: [RFC] a question about stack size form /proc/pid/task/child pid/limits

[Florian Weimer]

On 09/06/2017 04:14 AM, Xishi Qiu wrote:
> Hi, I find if I use a defined stack size to create a child thread,
> then the max stack size from /proc/pid/task/child pid/limits still
> shows "Max stack size            8388608", it doesn't update to
> the user defined size, is it a problem?

This reflects the maximum stack size of the main thread after execve. 
The size of the stack of the current thread is a separate matter; it can 
be located anywhere in the process image and much smaller or larger than 
the maximum size of the initial stack of the main thread.

Thanks,
Florian

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