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futex system call #2

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yashrajkakkad opened this issue Oct 24, 2021 · 1 comment
Open

futex system call #2

yashrajkakkad opened this issue Oct 24, 2021 · 1 comment
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Linux Compatibility Type: New Feature
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User Multi-threading

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@yashrajkakkad
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A key feature of Linux kernel - futex is not yet implemented.

For a start, two operations can be implemented:

  • FUTEX_WAIT - Test if the value at the futex contains the expected value. If so, sleep.
  • FUTEX_WAKE - Wake up a number of waiters waiting on the futex word.

A futex consists of a kernelspace wait queue that is attached to an atomic integer in userspace. I found something similar here which is used for implementing spinlock: wait_queue.rs

References:

@nuta I hope I am going in the right direction. I seek your valuable inputs to get started with the implementation.
@nuta
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nuta commented Oct 24, 2021

You're on the right tack, @yashrajkakkad! wait_queue.rs will be helpful to stop/resume threads on a futex. One thing I'd like you to keep in mind is I have never used directory or implemented futex(2). Please let me know if say something incorrect :)

BTW, when you port a new system call, I generally recommend to read its man page: https://man7.org/linux/man-pages/man2/futex.2.html

@castarco castarco mentioned this issue Oct 28, 2021
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nuta added a commit that referenced this issue Nov 4, 2021
@nuta
Embed a backtrace into Error in debug build
72554b4 
It helps where an error is constructed:

[   0.585] [7:curl] syscall: close(ffffffffffffffff, 0, 0, 0, 0, 0)
[   0.585] WARN: close: error: EBADF: This error originates from:
    #1: ffff800000184219  kerla::printk::capture_backtrace()+0x79
    #2: ffff8000001dbb13  kerla::result::Error::new()+0x23
    #3: ffff8000001dc0e7  <kerla::result::Error as c...la::result::Errno>>::from()+0x17
    #4: ffff800000211177  <T as core::convert::Into<U>>::into()+0x17
    #5: ffff8000001fcb55  kerla::fs::opened_file::OpenedFileTable::close()+0xa5
    #6: ffff80000010b124  kerla::syscalls::close::<i...yscallHandler>::sys_close()+0xa4
    #7: ffff80000011bf62  kerla::syscalls::SyscallHandler::do_dispatch()+0x4e62
    #8: ffff8000001168fc  kerla::syscalls::SyscallHandler::dispatch()+0x1ac
@UZER0 UZER0 mentioned this issue Nov 11, 2021
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@nuta nuta added this to the User Multi-threading milestone Nov 13, 2021
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@nuta @yashrajkakkad