On Thu, Apr 11, 2013 at 04:18:13PM +0300, Kirill A. Shutemov wrote: > Minchan Kim wrote: > > On Fri, Mar 29, 2013 at 09:04:16AM -0400, Sasha Levin wrote: > > > Hi all, > > > > > > While fuzzing with trinity inside a KVM tools guest running latest -next kernel, > > > I've stumbled on the following. > > > > > > It seems that the code in do_huge_pmd_wp_page() was recently modified in > > > "thp: do_huge_pmd_wp_page(): handle huge zero page". > > > > > > Here's the trace: > > > > > > [ 246.244708] BUG: unable to handle kernel paging request at ffff88009c422000 > > > [ 246.245743] IP: [<ffffffff81a0a795>] copy_page_rep+0x5/0x10 > > > [ 246.250569] PGD 7232067 PUD 7235067 PMD bfefe067 PTE 800000009c422060 > > > [ 246.251529] Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC > > > [ 246.252325] Dumping ftrace buffer: > > > [ 246.252791] (ftrace buffer empty) > > > [ 246.252869] Modules linked in: > > > [ 246.252869] CPU 3 > > > [ 246.252869] Pid: 11985, comm: trinity-child12 Tainted: G W 3.9.0-rc4-next-20130328-sasha-00014-g91a3267 #319 > > > [ 246.252869] RIP: 0010:[<ffffffff81a0a795>] [<ffffffff81a0a795>] copy_page_rep+0x5/0x10 > > > [ 246.252869] RSP: 0018:ffff88000015bc40 EFLAGS: 00010286 > > > [ 246.252869] RAX: ffff88000015bfd8 RBX: 0000000002710880 RCX: 0000000000000200 > > > [ 246.252869] RDX: 0000000000000000 RSI: ffff88009c422000 RDI: ffff88009a422000 > > > [ 246.252869] RBP: ffff88000015bc98 R08: 0000000002718000 R09: 0000000000000001 > > > [ 246.252869] R10: 0000000000000001 R11: 0000000000000000 R12: ffff880000000000 > > > [ 246.252869] R13: ffff88000015bfd8 R14: ffff88000015bfd8 R15: fffffffffff80000 > > > [ 246.252869] FS: 00007f53db93f700(0000) GS:ffff8800bba00000(0000) knlGS:0000000000000000 > > > [ 246.252869] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > > [ 246.252869] CR2: ffff88009c422000 CR3: 0000000000159000 CR4: 00000000000406e0 > > > [ 246.252869] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > > [ 246.252869] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 > > > [ 246.252869] Process trinity-child12 (pid: 11985, threadinfo ffff88000015a000, task ffff88009c60b000) > > > [ 246.252869] Stack: > > > [ 246.252869] ffffffff81234aae ffff88000015bc88 ffffffff81273639 0000000000a00000 > > > [ 246.252869] 0000000002718000 ffff8800ab36d050 ffff880000153800 ffffea0002690000 > > > [ 246.252869] 0000000000a00000 ffff8800ab36d000 ffffea0002710000 ffff88000015bd48 > > > [ 246.252869] Call Trace: > > > [ 246.252869] [<ffffffff81234aae>] ? copy_user_huge_page+0x1de/0x240 > > > [ 246.252869] [<ffffffff81273639>] ? mem_cgroup_charge_common+0xa9/0xc0 > > > [ 246.252869] [<ffffffff8126b4d7>] do_huge_pmd_wp_page+0x9f7/0xc60 > > > [ 246.252869] [<ffffffff81a0acd9>] ? __const_udelay+0x29/0x30 > > > [ 246.252869] [<ffffffff8123364e>] handle_mm_fault+0x26e/0x650 > > > [ 246.252869] [<ffffffff8117dc1a>] ? __lock_is_held+0x5a/0x80 > > > [ 246.252869] [<ffffffff83db3814>] ? __do_page_fault+0x514/0x5e0 > > > [ 246.252869] [<ffffffff83db3870>] __do_page_fault+0x570/0x5e0 > > > [ 246.252869] [<ffffffff811c6500>] ? rcu_eqs_exit_common+0x60/0x260 > > > [ 246.252869] [<ffffffff811c740e>] ? rcu_eqs_enter_common+0x33e/0x3b0 > > > [ 246.252869] [<ffffffff811c679c>] ? rcu_eqs_exit+0x9c/0xb0 > > > [ 246.252869] [<ffffffff83db3912>] do_page_fault+0x32/0x50 > > > [ 246.252869] [<ffffffff83db2ef0>] do_async_page_fault+0x30/0xc0 > > > [ 246.252869] [<ffffffff83db01e8>] async_page_fault+0x28/0x30 > > > [ 246.252869] Code: 90 90 90 90 90 90 9c fa 65 48 3b 06 75 14 65 48 3b 56 08 75 0d 65 48 89 1e 65 48 89 4e 08 9d b0 01 c3 9d 30 > > > c0 c3 b9 00 02 00 00 <f3> 48 a5 c3 0f 1f 80 00 00 00 00 eb ee 66 66 66 90 66 66 66 90 > > > [ 246.252869] RIP [<ffffffff81a0a795>] copy_page_rep+0x5/0x10 > > > [ 246.252869] RSP <ffff88000015bc40> > > > [ 246.252869] CR2: ffff88009c422000 > > > [ 246.252869] ---[ end trace 09fbe37b108d5766 ]--- > > > > > > And this is the code: > > > > > > if (is_huge_zero_pmd(orig_pmd)) > > > clear_huge_page(new_page, haddr, HPAGE_PMD_NR); > > > else > > > copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR); <--- this > > > > > > > > > Thanks, > > > Sasha > > > > I don't know this issue was already resolved. If so, my reply become a just > > question to Kirill regardless of this BUG. > > > > When I am looking at the code, I was wonder about the logic of GHZP(aka, > > get_huge_zero_page) reference handling. The logic depends on that page > > allocator never alocate PFN 0. > > > > Who makes sure it? What happens if allocator allocates PFN 0? > > I don't know all of architecture makes sure it. > > You investigated it for all arches? > > > > If not, > > CPU 1 CPU 2 CPU 3 > > > > shrink_huge_zero_page > > huge_zero_refcount = 0; > > GHZP > > pfn_0_zero_page = alloc_pages > > GHZP > > pfn_some_zero_page = alloc_page > > huge_zero_pfn = 0 > > huge_zero_pfn = pfn_0 > > huge_zero_refcount = 2 > > huge_zero_pfn = pfn_some > > huge_zero_refcount = 2 > > > > So, if you want to stick this logic, at least, don't we need BUG_ON to check > > pfn 0 allocation in get_huge_zero_page? > > I don't think it's related to oops in the thread (I was not able to > reproduce it), but nice catch anyway. > > What about the patch below? > > ===== > > >From 4579aefd606b2dd82797af163ce6d08912894b3a Mon Sep 17 00:00:00 2001 > From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> > Date: Thu, 11 Apr 2013 15:47:50 +0300 > Subject: [PATCH] thp: fix huge zero page logic for page with pfn == 0 > > Current implementation of huge zero page uses pfn value 0 to indicate > that the page hasn't allocated yet. It assumes that buddy page allocator > can't return page with pfn == 0. > > Let's rework the code to store 'struct page *' of huge zero page, not > its pfn. This way we can avoid the weak assumption. > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > Reported-by: Minchan Kim <minchan@xxxxxxxxxx> Looks nice to me. Acked-by: Minchan Kim <minchan@xxxxxxxxxx> -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>