Re: [BUG?] 2.6.x (2.6.13) - new signals not being delivered to a terminating (PF_EXITING) process.

From: linux-os (Dick Johnson)
Date: Tue Oct 11 2005 - 13:31:03 EST

On Tue, 11 Oct 2005, Kilau, Scott wrote:

> Hi everyone,
> This email will deal with the serial/tty layer of the kernel,
> but I don't think its completely isolated to this layer...
> I have found a problem with signals not getting delivered to a
> Process once it enters into the PF_EXITING state.
> Probably the best way to show it, is an example with the built-in
> COM port.
> 1) Don't have anything connected to COM1.
> 2) stty -ixon -ixoff -ixany crtscts < /dev/ttyS0
> 3) date > /dev/ttyS0
> 4) Press ctrl-c.
> The process does get this ctrl-c, and starts closing down.
> The serial driver gets its "tty close" for ttyS0, as it should,
> and goes into a "drain" waiting for the data that is pending
> in the UART to be written.
> (Which can never be written, because the port is stuck in a
> hardware flow control state)
> 5) Press ctrl-c again... And again, and again, and again. Nothing.
> The process is stuck, and a ps -ef shows that it is in a
> zombie state ([date])
> Under stock 2.4 kernels, the 2nd and subsequent ctrl-c's would wake
> up the serial driver's "wait" with a signal, which in turn would
> allow the serial driver to bail out of the forever "drain",
> and complete the close.
> Now, eventually, the "date" will bail, but only because the serial
> driver has a "timeout" set for the wait in its drain routine.
> It still never receives the 2nd+ ctrl-c's.
> Is this change intentional?
> If so, why?
> Thanks!
> Scott

Once a process in in the 'Z' state it should not receive any
signals. Its signal handlers are already gone. It's just a
snippit of sys_exit code that remains. If the process truly
is in the 'Z' state, its input/output/error file-descriptors
should have already been closed so the time-out from the
shutdown should have already happened.

Dick Johnson
Penguin : Linux version 2.6.13 on an i686 machine (5589.44 BogoMips).
Warning : 98.36% of all statistics are fiction.

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