Failure fork/exec/exec vs fork/exec/fork/exec

[Earl Chew]

We've come across a very subtle problem where child processes will
fail after some time. On our hyperthreaded systems, the child process
fails by consuming one thread, and degrading the system (typically
locking up the desktop) and power-off is the only recovery.

We use cygwin to provide a build system wrapper. Originally the
implementation would perform some configuration, then exec() the
build supervisor, and the build would proceed.

	bash -> fork/exec -> wrapper -> exec -> supervisor -> etc

This scenario fails as described above. The failure occurs after
some variable time, but typically within 10s of minutes.

We've noticed a couple of ways to workaround the problem:

   cmd.exe -> wrapper -> exec -> supervisor -> etc
   bash -> fork/exec -> wrapper -> fork/exec -> supervisor -> etc
   bash -> fork/exec -> wrapper -> spawn(_P_WAIT) -> supervisor -> etc

By experiment, it seems that the key to the failure is the sequence
of exec/exec, but I do not know how that corrupts the system so badly
that power off is the only recourse.

Earl


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