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Date: Tue, 14 Apr 2015 13:57:10 +0530 From: Preeti U Murthy <preeti@...ux.vnet.ibm.com> To: "Shreyas B. Prabhu" <shreyas@...ux.vnet.ibm.com>, linux-kernel@...r.kernel.org, Michael Ellerman <mpe@...erman.id.au>, "benh@...nel.crashing.org" <benh@...nel.crashing.org> CC: linuxppc-dev@...ts.ozlabs.org Subject: Re: [PATCH v4 3/3] powerpc/powernv: Introduce sysfs control for fastsleep workaround behavior Hi Shreyas, On 04/14/2015 07:26 AM, Shreyas B. Prabhu wrote: > + * fastsleep_workaround_state = WORKAROUND_APPLYONCE implies > + * fastsleep workaround needs to be left in 'applied' state on all > + * the cores. Do this by- > + * 1. Patching out the call to 'undo' workaround in fastsleep exit path > + * 2. Sending ipi to all the cores which have atleast one online thread > + * 3. Patching out the call to 'apply' workaround in fastsleep entry > + * path > + * There is no need to send ipi to cores which have all threads > + * offlined, as last thread of the core entering fastsleep or deeper > + * state would have applied workaround. > + */ > + err = patch_instruction( > + (unsigned int *)pnv_fastsleep_workaround_at_exit, > + PPC_INST_NOP); > + if (err) { > + pr_err("fastsleep_workaround_state change failed while patching pnv_fastsleep_workaround_at_exit"); > + goto fail; > + } > + > + primary_thread_mask = cpu_online_cores_map(); > + on_each_cpu_mask(&primary_thread_mask, > + pnv_fastsleep_workaround_apply, > + &err, 1); > + if (err) { > + pr_err("fastsleep_workaround_state change failed while running pnv_fastsleep_workaround_apply"); > + goto fail; > + } > + > + err = patch_instruction( > + (unsigned int *)pnv_fastsleep_workaround_at_entry, > + PPC_INST_NOP); > + if (err) { > + pr_err("fastsleep_workaround_state change failed while patching pnv_fastsleep_workaround_at_entry"); > + goto fail; > + } A point that bothers me here is if we can potentially race with cpu hotplug ? If cpuX and its siblings are offline and it was interrupted to come online: cpuX cpuY Interrupted to come online Undo workaround Nop the fastsleep_workaround_exit path IPI online cores: apply workaround once Set yourself in the online mask Nop the fastsleep_workaround_entry path This results in cpuX undoing the workaround on its core, never to set it back again. So should we protect the region between the beginning and end of patching instructions with get_online_cpus() and put_online_cpus() ? Regards Preeti U Murthy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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