On Tue, 28 Jun 2016 11:53:13 +0800 Simon Guo <simon...@linux.vnet.ibm.com> wrote:
> hi Cyril, > > On Wed, Jun 08, 2016 at 02:00:34PM +1000, Cyril Bur wrote: > > @@ -1108,11 +1084,11 @@ struct task_struct *__switch_to(struct task_struct > > *prev, > > */ > > save_sprs(&prev->thread); > > > > - __switch_to_tm(prev); > > - > > /* Save FPU, Altivec, VSX and SPE state */ > > giveup_all(prev); > > > > + __switch_to_tm(prev); > > + > Hi Simon, > There should be a bug. > giveup_all() will clear MSR[FP] bit. > __switch_to_tm() reads that bit to decide whether the FP > register needs to be flushed to thread_struct. > === tm_reclaim() (invoked by __switch_to_tm)======================== > andi. r0, r4, MSR_FP > beq dont_backup_fp > > addi r7, r3, THREAD_CKFPSTATE > SAVE_32FPRS_VSRS(0, R6, R7) /* r6 scratch, r7 transact fp > state */ > > mffs fr0 > stfd fr0,FPSTATE_FPSCR(r7) > > dont_backup_fp: > ============================= > > But now the __switch_to_tm() is moved behind giveup_all(). > So __switch_to_tm() loses MSR[FP] and cannot decide whether saving ckpt FPU > or not. > Good catch! Yes it looks that way indeed. I thought I had a test to catch this because this is the big risk here but upon reflection it looks like I don't (mostly because it seems a condition to catch that is hard to craft). I'll add a test and a fix. Thanks. Cyril > The same applies to VMX/VSX. Yeah. > > Thanks, > - Simon > _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
