[PATCH v2 18/20] powerpc: tm: Always use fp_state and vr_state to store live registers
wei.guo.simon at gmail.com
Mon Aug 15 19:42:02 AEST 2016
On Mon, Aug 15, 2016 at 05:25:53PM +1000, Cyril Bur wrote:
> > There are 2 "giveall_all()" in above path:
> > __switch_to()
> > giveup_all() // first time
> > __switch_to_tm()
> > tm_reclaim_task()
> > tm_reclaim_thread()
> > giveup_all() // again????
> > We should remove the one in __switch_to().
> I don't think that will be possible, if a thread is not transactional
> the second giveup_all() won't get called so we'll need to preserve the
> one in __switch_to().
> I don't think removing the second is a good idea as we can enter
> tm_reclaim_thread() from other means than __switch_to_tm().
> I did think that perhaps __switch_to_tm() could call giveup_all() in
> the non transactional case but on reflection, doing nothing on the non
> transactional case is cleaner.
> The two calls are annoying but in the case where two calls are made,
> the second should realise that nothing needs to be done and exit
Ah, yes. I somehow ignored non-transactional case....
> > And another question, for following code in tm_reclaim_thread():
> > /* Having done the reclaim, we now have the checkpointed
> > * FP/VSX values in the registers. These might be valid
> > * even if we have previously called enable_kernel_fp() or
> > * flush_fp_to_thread(), so update thr->regs->msr to
> > * indicate their current validity.
> > */
> > thr->regs->msr |= msr_diff;
> > Does it imply the task being switched out of CPU, with TIF_RESTORE_TM
> > bit set, might end with MSR_FP enabled? (I thought MSR_FP should
> > not
> > be enabled for a switched out task, as specified in
> > flush_fp_to_thread())
> Correct! I mistakenly thought it was solving a problem but you're
> right. What you say is correct but it breaks signals, I've been
> hesitating on how to get signals to work with the correct solution
> here, I wasn't happy with my ideas but looks like it's pretty much the
> only way to go unfortunately.
Currently there will be an oops on flush_fp_to_thread() with this
patch, when ptrace a transaction application.
I think originally there is no giveup_all() call before tm_reclaim_thread(),
so TIF_RESTORE_TM bit is not set. And finally thr->regs->msr is not
marked with MSR_FP enabled.
[ 363.473851] kernel BUG at arch/powerpc/kernel/process.c:191!
[ 363.474242] Oops: Exception in kernel mode, sig: 5 [#1]
[ 363.474595] SMP NR_CPUS=2048 NUMA pSeries
[ 363.474956] Modules linked in: isofs sg virtio_balloon ip_tables xfs libcrc32c sr_mod cdrom sd_mod virtio_net ibmvscsi scsi_transport_srp virtio_pci virtio_ring virtio
[ 363.476021] CPU: 0 PID: 3018 Comm: ptrace-tm-gpr Not tainted 4.8.0-rc1+ #5
[ 363.476547] task: c000000072c66b80 task.stack: c00000007e64c000
[ 363.476949] NIP: c000000000017650 LR: c00000000000dc10 CTR: c000000000011538
[ 363.477428] REGS: c00000007e64f960 TRAP: 0700 Not tainted (4.8.0-rc1+)
[ 363.477948] MSR: 8000000000029033 <SF,EE,ME,IR,DR,RI,LE> CR: 42000088 XER: 20000000
[ 363.478488] CFAR: c000000000017620 SOFTE: 1
GPR00: c00000000000dc10 c00000007e64fbe0 c000000000f3d800 c000000072c65600
GPR04: c0000000008706a8 0000000000000000 0000000000000108 0000000000000000
GPR08: 0000010008410180 0000000000000001 0000000000000001 c000000000870f18
GPR12: 0000000000000000 c00000000fe80000 0000000000000000 0000000000000000
GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
GPR24: 0000000000000000 0000000000000000 0000000000000000 0000010008410180
GPR28: 0000000000000000 0000000000000000 0000000000000108 c000000072c65600
[ 363.482451] NIP [c000000000017650] flush_fp_to_thread+0x50/0x70
[ 363.482855] LR [c00000000000dc10] fpr_get+0x40/0x120
[ 363.483194] Call Trace:
[ 363.483362] [c00000007e64fbe0] [c00000007e64fcf0] 0xc00000007e64fcf0 (unreliable)
[ 363.483872] [c00000007e64fc00] [c00000000000dc10] fpr_get+0x40/0x120
[ 363.484304] [c00000007e64fd60] [c000000000011578] arch_ptrace+0x628/0x7e0
[ 363.485811] [c00000007e64fde0] [c0000000000c3340] SyS_ptrace+0xa0/0x180
[ 363.486276] [c00000007e64fe30] [c000000000009404] system_call+0x38/0xec
[ 363.486725] Instruction dump:
[ 363.486927] 40820010 4e800020 60000000 60420000 7c0802a6 f8010010 f821ffe1 e92d0210
[ 363.487459] 7c694a78 7d290074 7929d182 69290001 <0b090000> 4bffff25 38210020 e8010010
[ 363.488005] ---[ end trace 58650a99c675b48c ]---
[ 365.490279] Kernel panic - not syncing: Fatal exception
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