Re: Strange intermittent EIO error when writing to stdout since v3.8.0

[Rob Landley <rob@landley.net>]

On 06/06/2013 06:54:17 AM, Markus Trippelsdorf wrote:
> Since v3.8.0 several people reported intermittent IO errors that  
> happen
> during high system load while using "emerge" under Gentoo:
...
> see: https://bugs.gentoo.org/show_bug.cgi?id=459674
> 
> (A similar issue also happens when building Firefox since v3.8.0. But
> because Firefox's build process doesn't raise an exception it just  
> dies
> at random points without giving a clue.)
> 
> Now the question is: Could this be a kernel bug? Maybe in the TTY  
> layer?
> 
> Unfortunately the issue is not easily reproducible and a git-bisect is
> out of the question.

I tracked down and fixed something like this in the User Mode Linux tty  
implementation many moons ago.

The trick to making it reproducible was to rename a copy of the xterm  
binary to somethingunique, run a shell in said xterm (because "cat"  
doesn't exercise the tty logic, that's why), run a thing in there  
producing test output, and have a loop in another window doing "while  
true; do killall -STOP somethingunique; sleep 1; killall -START  
somethingunique; sleep 1; done".

This forces the pipe buffer to the pty to fill up and exercise the flow  
control logic, plus all the fun "short write and retry" stuff...

Rob