On Mon, May 20, 2019 at 12:02:23PM +1000, Michael Ellerman wrote: > Bharata B Rao <bharata@xxxxxxxxxxxxx> writes: > > On Thu, May 16, 2019 at 07:44:20PM +0530, srikanth wrote: > >> Hello, > >> > >> On power9 host, performing memory hotunplug from ppc64le guest results in > >> kernel oops. > >> > >> Kernel used : https://github.com/torvalds/linux/tree/v5.1 built using > >> ppc64le_defconfig for host and ppc64le_guest_defconfig for guest. > >> > >> Recreation steps: > >> > >> 1. Boot a guest with below mem configuration: > >> <maxMemory slots='32' unit='KiB'>33554432</maxMemory> > >> <memory unit='KiB'>8388608</memory> > >> <currentMemory unit='KiB'>4194304</currentMemory> > >> <cpu> > >> <numa> > >> <cell id='0' cpus='0-31' memory='8388608' unit='KiB'/> > >> </numa> > >> </cpu> > >> > >> 2. From host hotplug 8G memory -> verify memory hotadded succesfully -> now > >> reboot guest -> once guest comes back try to unplug 8G memory > >> > >> mem.xml used: > >> <memory model='dimm'> > >> <target> > >> <size unit='GiB'>8</size> > >> <node>0</node> > >> </target> > >> </memory> > >> > >> Memory attach and detach commands used: > >> virsh attach-device vm1 ./mem.xml --live > >> virsh detach-device vm1 ./mem.xml --live > >> > >> Trace seen inside guest after unplug, guest just hangs there forever: > >> > >> [ 21.962986] kernel BUG at arch/powerpc/mm/pgtable-frag.c:113! > >> [ 21.963064] Oops: Exception in kernel mode, sig: 5 [#1] > >> [ 21.963090] LE PAGE_SIZE=64K MMU=Radix MMU=Hash SMP NR_CPUS=2048 NUMA > >> pSeries > >> [ 21.963131] Modules linked in: xt_tcpudp iptable_filter squashfs fuse > >> vmx_crypto ib_iser rdma_cm iw_cm ib_cm ib_core libiscsi scsi_transport_iscsi > >> ip_tables x_tables autofs4 btrfs zstd_decompress zstd_compress lzo_compress > >> raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx > >> xor raid6_pq multipath crc32c_vpmsum > >> [ 21.963281] CPU: 11 PID: 316 Comm: kworker/u64:5 Kdump: loaded Not > >> tainted 5.1.0-dirty #2 > >> [ 21.963323] Workqueue: pseries hotplug workque pseries_hp_work_fn > >> [ 21.963355] NIP: c000000000079e18 LR: c000000000c79308 CTR: > >> 0000000000008000 > >> [ 21.963392] REGS: c0000003f88034f0 TRAP: 0700 Not tainted (5.1.0-dirty) > >> [ 21.963422] MSR: 800000000282b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE> CR: > >> 28002884 XER: 20040000 > >> [ 21.963470] CFAR: c000000000c79304 IRQMASK: 0 > >> [ 21.963470] GPR00: c000000000c79308 c0000003f8803780 c000000001521000 > >> 0000000000fff8c0 > >> [ 21.963470] GPR04: 0000000000000001 00000000ffe30005 0000000000000005 > >> 0000000000000020 > >> [ 21.963470] GPR08: 0000000000000000 0000000000000001 c00a000000fff8e0 > >> c0000000016d21a0 > >> [ 21.963470] GPR12: c0000000016e7b90 c000000007ff2700 c00a000000a00000 > >> c0000003ffe30100 > >> [ 21.963470] GPR16: c0000003ffe30000 c0000000014aa4de c00a0000009f0000 > >> c0000000016d21b0 > >> [ 21.963470] GPR20: c0000000014de588 0000000000000001 c0000000016d21b8 > >> c00a000000a00000 > >> [ 21.963470] GPR24: 0000000000000000 ffffffffffffffff c00a000000a00000 > >> c0000003ffe96000 > >> [ 21.963470] GPR28: c00a000000a00000 c00a000000a00000 c0000003fffec000 > >> c00a000000fff8c0 > >> [ 21.963802] NIP [c000000000079e18] pte_fragment_free+0x48/0xd0 > >> [ 21.963838] LR [c000000000c79308] remove_pagetable+0x49c/0x5b4 > >> [ 21.963873] Call Trace: > >> [ 21.963890] [c0000003f8803780] [c0000003ffe997f0] 0xc0000003ffe997f0 > >> (unreliable) > >> [ 21.963933] [c0000003f88037b0] [0000000000000000] (null) > >> [ 21.963969] [c0000003f88038c0] [c00000000006f038] > >> vmemmap_free+0x218/0x2e0 > >> [ 21.964006] [c0000003f8803940] [c00000000036f100] > >> sparse_remove_one_section+0xd0/0x138 > >> [ 21.964050] [c0000003f8803980] [c000000000383a50] > >> __remove_pages+0x410/0x560 > >> [ 21.964093] [c0000003f8803a90] [c000000000c784d8] > >> arch_remove_memory+0x68/0xdc > >> [ 21.964136] [c0000003f8803ad0] [c000000000385d74] > >> __remove_memory+0xc4/0x110 > >> [ 21.964180] [c0000003f8803b10] [c0000000000d44e4] > >> dlpar_remove_lmb+0x94/0x140 > >> [ 21.964223] [c0000003f8803b50] [c0000000000d52b4] > >> dlpar_memory+0x464/0xd00 > >> [ 21.964259] [c0000003f8803be0] [c0000000000cd5c0] > >> handle_dlpar_errorlog+0xc0/0x190 > >> [ 21.964303] [c0000003f8803c50] [c0000000000cd6bc] > >> pseries_hp_work_fn+0x2c/0x60 > >> [ 21.964346] [c0000003f8803c80] [c00000000013a4a0] > >> process_one_work+0x2b0/0x5a0 > >> [ 21.964388] [c0000003f8803d10] [c00000000013a818] > >> worker_thread+0x88/0x610 > >> [ 21.964434] [c0000003f8803db0] [c000000000143884] kthread+0x1a4/0x1b0 > >> [ 21.964468] [c0000003f8803e20] [c00000000000bdc4] > >> ret_from_kernel_thread+0x5c/0x78 > >> [ 21.964506] Instruction dump: > >> [ 21.964527] fbe1fff8 f821ffd1 78638502 78633664 ebe90000 7fff1a14 > >> 395f0020 813f0020 > >> [ 21.964569] 7d2907b4 7d2900d0 79290fe0 69290001 <0b090000> 7c0004ac > >> 7d205028 3129ffff > >> [ 21.964613] ---[ end trace aaa571aa1636fee6 ]--- > >> [ 21.966349] > >> [ 21.966383] Sending IPI to other CPUs > >> [ 21.978335] IPI complete > >> [ 21.981354] kexec: Starting switchover sequence. > >> I'm in purgatory > > > > git bisect points to > > > > commit 4231aba000f5a4583dd9f67057aadb68c3eca99d > > Author: Nicholas Piggin <npiggin@xxxxxxxxx> > > Date: Fri Jul 27 21:48:17 2018 +1000 > > > > powerpc/64s: Fix page table fragment refcount race vs speculative references > > > > The page table fragment allocator uses the main page refcount racily > > with respect to speculative references. A customer observed a BUG due > > to page table page refcount underflow in the fragment allocator. This > > can be caused by the fragment allocator set_page_count stomping on a > > speculative reference, and then the speculative failure handler > > decrements the new reference, and the underflow eventually pops when > > the page tables are freed. > > > > Fix this by using a dedicated field in the struct page for the page > > table fragment allocator. > > > > Fixes: 5c1f6ee9a31c ("powerpc: Reduce PTE table memory wastage") > > Cc: stable@xxxxxxxxxxxxxxx # v3.10+ > > That's the commit that added the BUG_ON(), so prior to that you won't > see the crash. Right, but the commit says it fixes page table page refcount underflow by introducing a new field &page->pt_frag_refcount. Now we are hitting the underflow for this pt_frag_refcount. BTW, if I go below this commit, I don't hit the pagecount VM_BUG_ON_PAGE(page_ref_count(page) == 0, page); which is in pte_fragment_free() path. Regards, Bharata.
