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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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