[6049] in Athena Bugs
RT kernel sys/ca/mc881.c
daemon@ATHENA.MIT.EDU (John Carr)
Sun Sep 16 23:30:15 1990
To: bugs@ATHENA.MIT.EDU
Date: Sun, 16 Sep 90 23:30:04 EDT
From: John Carr <jfc@ATHENA.MIT.EDU>
The function mc881_abort() in the RT kernel can enter an infinite loop. Since
this function is run at raised priority in kernel mode, this hangs the
machine.
The fix is to put a timeout in the first loop in this function:
if (ior(IOIM2+IOIM_CPS)&IOIM_CPS_68881_BUSY) { /* If the 881 is busy */
do {
i = MC_CIR_READ_16(MC_CIR_RESPONSE);
} while ((i&MC_RESPONSE_CA)
&& ((i&MC_RESPONSE_NULL_MASK) == MC_RESPONSE_NULL_VALUE));
}
should read something like:
if (ior(IOIM2+IOIM_CPS)&IOIM_CPS_68881_BUSY) { /* If the 881 is busy */
int j = 1000000;
do {
i = MC_CIR_READ_16(MC_CIR_RESPONSE);
} while ((i&MC_RESPONSE_CA)
&& ((i&MC_RESPONSE_NULL_MASK) == MC_RESPONSE_NULL_VALUE)
&& j-- > 0);
if(j == 0) panic("mc881_abort timeout");
}
I don't know if the panic is needed or if it is safe to continue.
I will attempt to demonstrate this to anyone who is interested (but not on my
machine). It can be done from an unprivileged user mode program.
