Messages in this thread | | | Date | Mon, 19 Aug 2002 21:37:16 +0200 (CEST) | From | Ingo Molnar <> | Subject | Re: [patch] O(1) sys_exit(), threading, scalable-exit-2.5.31-A6 |
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On Mon, 19 Aug 2002, Dave McCracken wrote:
> In looking at the code I was wondering something. What happens to the > real parent of a ptraced task when it calls wait4()? If that's its only > child, won't it return ECHILD?
yes, this is ugly beyond belief.
eg. under bash start up some code that blocks, eg:
# cat
the shell will not display a prompt, it wait4()s for the 'cat' process to exit.
strace the bash PID - it shows the wait4().
strace 'cat' PID (via strace -p) and keep the strace running - it will show 'cat' blocked on console input. [some signal like this could happen to a shell anyway, in a reasonably complex script.]
now do something that breaks bash out of its wait4 - eg. send a 'kill -SIGCONT BASH_PID' signal - bash returns with a prompt! The 'cat' becomes a 'background' task - and it gets majorly confused when doing the next shell command in bash - it displays "cat: -: Input/output error" and goes zombie.
ptrace is clearly broken - and i tested this with a stock 2.4 kernel.
Ingo
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