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Under certain loads, this soft lockup has been observed: BUG: soft lockup - CPU#2 stuck for 22s! [ip6tables:1016] Modules linked in: ip6t_rpfilter ip6t_REJECT cfg80211 rfkill xt_conntrack ebtable_nat ebtable_broute bridge stp llc ebtable_filter ebtables ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_security ip6table_raw ip6table_filter ip6_tables iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_security iptable_raw vfat fat efivarfs xfs libcrc32c CPU: 2 PID: 1016 Comm: ip6tables Not tainted 3.13.0-0.rc7.30.sa2.aarch64 #1 task: fffffe03e81d1400 ti: fffffe03f01f8000 task.ti: fffffe03f01f8000 PC is at __cpu_flush_kern_tlb_range+0xc/0x40 LR is at __purge_vmap_area_lazy+0x28c/0x3ac pc : [<fffffe000009c5cc>] lr : [<fffffe0000182710>] pstate: 80000145 sp : fffffe03f01fbb70 x29: fffffe03f01fbb70 x28: fffffe03f01f8000 x27: fffffe0000b19000 x26: 00000000000000d0 x25: 000000000000001c x24: fffffe03f01fbc50 x23: fffffe03f01fbc58 x22: fffffe03f01fbc10 x21: fffffe0000b2a3f8 x20: 0000000000000802 x19: fffffe0000b2a3c8 x18: 000003fffdf52710 x17: 000003ff9d8bb910 x16: fffffe000050fbfc x15: 0000000000005735 x14: 000003ff9d7e1a5c x13: 0000000000000000 x12: 000003ff9d7e1a5c x11: 0000000000000007 x10: fffffe0000c09af0 x9 : fffffe0000ad1000 x8 : 000000000000005c x7 : fffffe03e8624000 x6 : 0000000000000000 x5 : 0000000000000000 x4 : 0000000000000000 x3 : fffffe0000c09cc8 x2 : 0000000000000000 x1 : 000fffffdfffca80 x0 : 000fffffcd742150 The __cpu_flush_kern_tlb_range() function looks like: ENTRY(__cpu_flush_kern_tlb_range) dsb sy lsr x0, x0, #12 lsr x1, x1, #12 1: tlbi vaae1is, x0 add x0, x0, #1 cmp x0, x1 b.lo 1b dsb sy isb ret ENDPROC(__cpu_flush_kern_tlb_range) The above soft lockup shows the PC at tlbi insn with: x0 = 0x000fffffcd742150 x1 = 0x000fffffdfffca80 So __cpu_flush_kern_tlb_range has 0x128ba930 tlbi flushes left after it has already been looping for 23 seconds!. Looking up one frame at __purge_vmap_area_lazy(), there is: ... list_for_each_entry_rcu(va, &vmap_area_list, list) { if (va->flags & VM_LAZY_FREE) { if (va->va_start < *start) *start = va->va_start; if (va->va_end > *end) *end = va->va_end; nr += (va->va_end - va->va_start) >> PAGE_SHIFT; list_add_tail(&va->purge_list, &valist); va->flags |= VM_LAZY_FREEING; va->flags &= ~VM_LAZY_FREE; } } ... if (nr || force_flush) flush_tlb_kernel_range(*start, *end); So if two areas are being freed, the range passed to flush_tlb_kernel_range() may be as large as the vmalloc space. For arm64, this is ~240GB for 4k pagesize and ~2TB for 64kpage size. This patch works around this problem by adding a loop limit. If the range is larger than the limit, use flush_tlb_all() rather than flushing based on individual pages. The limit chosen is arbitrary as the TLB size is implementation specific and not accessible in an architected way. The aim of the arbitrary limit is to avoid soft lockup. Signed-off-by: Mark Salter <msalter@redhat.com> [catalin.marinas@arm.com: commit log update] [catalin.marinas@arm.com: marginal optimisation] [catalin.marinas@arm.com: changed to MAX_TLB_RANGE and added comment] Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> |
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