From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp-out.google.com (smtp-out.google.com [74.125.121.67]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 08E86B6F1E for ; Thu, 30 Dec 2010 10:05:23 +1100 (EST) Received: from wpaz1.hot.corp.google.com (wpaz1.hot.corp.google.com [172.24.198.65]) by smtp-out.google.com with ESMTP id oBTMsvMc029833 for ; Wed, 29 Dec 2010 14:54:58 -0800 Received: from iwn2 (iwn2.prod.google.com [10.241.68.66]) by wpaz1.hot.corp.google.com with ESMTP id oBTMsuC2029528 (version=TLSv1/SSLv3 cipher=RC4-MD5 bits=128 verify=NOT) for ; Wed, 29 Dec 2010 14:54:56 -0800 Received: by iwn2 with SMTP id 2so11301975iwn.21 for ; Wed, 29 Dec 2010 14:54:56 -0800 (PST) Date: Wed, 29 Dec 2010 14:54:49 -0800 (PST) From: Hugh Dickins To: Ben Herrenschmidt Subject: PowerPC BUG: using smp_processor_id() in preemptible code Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: Jeremy Fitzhardinge , linuxppc-dev@lists.ozlabs.org, Nick Piggin , linux-kernel@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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)