Jun Sun wrote:
On Mon, Apr 18, 2005 at 01:32:46PM +0400, Pavel Kiryukhin wrote:
Hi,
the preempt_disable/preempt_enable sequence in do_cpu() [traps.c]
exists quite long (patch submitted in Oct. 2004), so it should be nothing
wrong there.
Can somebody please comment why use of preempt_disable/enable in do_cpu
will not result in "scheduling while atomic" for fpu-less cpu (with enabled
preemption).
The sequence looks like
do_cpu()
| preempt_disable()
| fpu_emulator_cop1Handler()
| | cond_reshed()
| | | schedule() <------ scheduling while atomic
The proposed patch was tested for Sibyte, but it has fpu (AFAIK) and has no
fpu_emulator_cop1Handler called.
fpu_emulator maintains global variables and in general is dangerous
to be preempted in the middle of processing.
The quick fix for this problem is probably to move preemption disabling/
enabling inside fpu_emulator_cop1Handler().
Better fix is probably to modify fpu emulator so that it is preemption
safe overall.
Jun
Missed this one ! I had a patch that enables preemption before the
cond_resched and disables right after it. I forgot to send it to
linux-mips though. But, I needed it to work on fpu-less CPU. My bad.
Thanks
Manish Lachwani
