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

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