Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754114Ab0L2WzT (ORCPT ); Wed, 29 Dec 2010 17:55:19 -0500 Received: from smtp-out.google.com ([74.125.121.67]:24369 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753949Ab0L2WzQ (ORCPT ); Wed, 29 Dec 2010 17:55:16 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=date:from:x-x-sender:to:cc:subject:message-id:user-agent :mime-version:content-type; b=t/DA+tJ2OzmlyHPJPeDuGX9g8PKrlpylmtzHuWpmdymiO2QNJiXpIpSknrBRqgkARE unxitkosnApR97edaZHw== Date: Wed, 29 Dec 2010 14:54:49 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@sister.anvils To: Ben Herrenschmidt cc: Jeremy Fitzhardinge , Nick Piggin , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: PowerPC BUG: using smp_processor_id() in preemptible code Message-ID: User-Agent: Alpine 2.00 (LSU 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2833 Lines: 62 With recent 2.6.37-rc, with CONFIG_PREEMPT=y CONFIG_DEBUG_PREEMPT=y on the PowerPC G5, I get spammed by BUG warnings each time I swapoff: BUG: using smp_processor_id() in preemptible [00000000] code: swapoff/3974 caller is .hpte_need_flush+0x4c/0x2e8 Call Trace: [c0000001b4a3f830] [c00000000000f3cc] .show_stack+0x6c/0x16c (unreliable) [c0000001b4a3f8e0] [c00000000023eda0] .debug_smp_processor_id+0xe4/0x11c [c0000001b4a3f970] [c00000000002f2f4] .hpte_need_flush+0x4c/0x2e8 [c0000001b4a3fa30] [c0000000000e7ef8] .vunmap_pud_range+0x148/0x200 [c0000001b4a3fb10] [c0000000000e8058] .vunmap_page_range+0xa8/0xd4 [c0000001b4a3fbb0] [c0000000000e80a4] .free_unmap_vmap_area+0x20/0x38 [c0000001b4a3fc40] [c0000000000e8138] .remove_vm_area+0x7c/0xb4 [c0000001b4a3fcd0] [c0000000000e8308] .__vunmap+0x50/0x104 [c0000001b4a3fd60] [c0000000000ef3fc] .SyS_swapoff+0x59c/0x6a8 [c0000001b4a3fe30] [c0000000000075a8] syscall_exit+0x0/0x40 I notice hpte_need_flush() itself acknowledges * Must be called from within some kind of spinlock/non-preempt region... Though I didn't actually bisect, I believe this is since Jeremy's 64141da587241301ce8638cc945f8b67853156ec "vmalloc: eagerly clear ptes on vunmap", which moves a call to vunmap_page_range() from one place (which happened to be inside a spinlock) to another (where it's not). I guess my warnings would be easily silenced by moving that call to vunmap_page_range() down just inside the spinlock below it; but I'm dubious that that's the right fix - it looked as if there are other paths through vmalloc.c where vunmap_page_range() has been getting called without preemption disabled, long before Jeremy's change, just paths that I never happen to go down in my limited testing. For the moment I'm using the obvious patch below to keep it quiet; but I doubt that this is the right patch either. I'm hoping that ye who understand the importance of hpte_need_flush() will be best able to judge what to do. Or might there be other architectures expecting to be unpreemptible there? Thanks, Hugh --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -37,11 +37,13 @@ static void vunmap_pte_range(pmd_t *pmd, { pte_t *pte; + preempt_disable(); /* Stop __vunmap() triggering smp_processor_id() in preemptible from hpte_need_flush() */ pte = pte_offset_kernel(pmd, addr); do { pte_t ptent = ptep_get_and_clear(&init_mm, addr, pte); WARN_ON(!pte_none(ptent) && !pte_present(ptent)); } while (pte++, addr += PAGE_SIZE, addr != end); + preempt_enable(); } static void vunmap_pmd_range(pud_t *pud, unsigned long addr, unsigned long end) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/