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
