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    SubjectRe: 3.0.18 tcsetattr on fd 0 when detached freezes system (RCU timeouts) (Centos 6.1 x86_64)
    On 28.01.2012 04:43, Professor Berkley Shands wrote:
    >
    > typedef struct
    > {
    > struct termios term;
    > } XKEY_DATA;
    >
    > typedef XKEY_DATA *xkeyhandle;
    >
    > static inline xkeyhandle xkeystart()
    > {
    >
    > // Turn off echo.
    > struct termios temp;
    > err = tcgetattr(0, &temp);
    > if (err)
    > {
    > perror("tcgetattr failure");
    > }
    >
    > XKEY_DATA *handle = new XKEY_DATA;
    > handle->term = temp;
    >
    > temp.c_lflag &= ~ECHO;
    > temp.c_lflag &= ~ICANON;
    >
    > err = tcsetattr(0, TCSANOW, &temp); // this line causes the kernel to get very sick
    > if (err)
    > {
    > perror("tcsetattr failure");
    > }
    >
    > return handle;
    >
    > }
    >
    > The above code, called from main() will produce an error from tcsh:
    >
    > /home/bshands> ./a.out > /dev/null &
    > [1] 3635
    > /home/bshands>
    > /home/bshands>
    > [1] + Suspended (tty output) ./a.out > /dev/null
    > /home/bshands>
    >
    > this does not appear on the redhat kernel, nor 2.6.32.43, but appeared infrequently in 3.0.9.
    > in 3.0.18, doing this in the background does *EVIL* things.
    >
    > ssh system "./a.out > /dev/null &" &
    >
    > Now when the code reaches the tcsetattr() the system quits scheduling tasks.
    > top shows 100%sy on 4/12 cores, kernel threads blocked, stalled tasks count increasing.

    I used the following code:

    =======================================
    #include <termios.h>
    #include <stdio.h>

    int main() {
    struct termios temp;

    if (tcgetattr(0, &temp) != 0)
    perror("tcgetattr failure");

    temp.c_lflag &= ~ECHO;
    temp.c_lflag &= ~ICANON;

    if (tcsetattr(0, TCSANOW, &temp) != 0) // this line causes the kernel to get very sick
    perror("tcsetattr failure");

    return 0;
    }
    =======================================


    But can't reproduce what you're observing. It prints

    tcgetattr failure: Inappropriate ioctl for device
    tcsetattr failure: Inappropriate ioctl for device

    and does not do any evil things. I tried it on 3.0.18
    on x86 on 32bits and 64bits.

    What I'm doing wrong?

    Thanks,

    /mjt


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