On x86 Linux 2.2.12 a valid ptrace call that closely follows a
successful PTRACE_ATTACH can fail, with error ESRCH.
For example, I find that if I make two calls like this
ret = ptrace(PTRACE_ATTACH, pid, 0, 0);
ret = ptrace(PTRACE_DETACH, pid, 0, 0);
the second call will fail, with ESRCH.
However, if I put some time between the calls, like this
ret = ptrace(PTRACE_ATTACH, pid, 0, 0);
usleep(100);
ret = ptrace(PTRACE_DETACH, pid, 0, 0);
then the second call will succeed.
My guess is that the traced process has not had its state set to
TASK_STOPPED before the second call to ptrace is executed. (Does the
traced process need to be scheduled before it will change to
TASK_STOPPED?)
Does anyone know for sure why this happens?
Can anyone suggest a workaround that to allow me make one or
more ptrace calls immediately after a PTRACE_ATTACH?
Thanks.
Vic Zandy
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