From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-x244.google.com (mail-pf0-x244.google.com [IPv6:2607:f8b0:400e:c00::244]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3sCVrb52sdzDr0d for ; Mon, 15 Aug 2016 19:42:07 +1000 (AEST) Received: by mail-pf0-x244.google.com with SMTP id h186so3490016pfg.2 for ; Mon, 15 Aug 2016 02:42:07 -0700 (PDT) Date: Mon, 15 Aug 2016 17:42:02 +0800 From: Simon Guo To: Cyril Bur Cc: linuxppc-dev@lists.ozlabs.org, anton@samba.org, mikey@neuling.org Subject: Re: [PATCH v2 18/20] powerpc: tm: Always use fp_state and vr_state to store live registers Message-ID: <20160815094201.GA32347@simonLocalRHEL7.x64> References: <20160811232819.11453-1-cyrilbur@gmail.com> <20160811232819.11453-19-cyrilbur@gmail.com> <20160814015602.GA21144@simonLocalRHEL7.x64> <1471245953.24478.0.camel@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 In-Reply-To: <1471245953.24478.0.camel@gmail.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Hi Cyril, 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 > quickly. 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 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 ]--- [ 363.490137] [ 365.490279] Kernel panic - not syncing: Fatal exception Thanks, - Simon