最近遇到一个suse的crash 问题：
我没有使用 mkswap /dev/磁盘路径 来制作swap分区，我有很多剩余内存，我设置nr_swapfiles为0，可是我还是遇到了关于swap的crash。
We got more kernel crashes at swapin_readahead() on our kernel： [ 948.894273] BUG: unable to handle kernel NULL pointer dereference at 000000000000000c [ 948.894283] IP: [<ffffffff81133662>] valid_swaphandles+0x72/0x150 [ 948.894292] PGD 3e4b007067 PUD 3e4b008067 PMD 0 [ 948.894296] Oops: 0000 [#1] SMP [ 948.894301] CPU 29 [ 948.894302] Modules linked in: xfs w83627dhg(EN) af_packet tipc(EX) ossmod(EN) iptable_filter ip_tables x_tables bonding edd cpufreq_conservative cpufreq_userspace cpufreq_po wersave acpi_cpufreq mperf binfmt_misc fuse loop dm_mod ipv6 ipv6_lib pcspkr i40e(EX) igb ses enclosure dca iTCO_wdt sg ptp pps_core i2c_i801 iTCO_vendor_support mei mptctl mptb ase rtc_cmos button acpi_power_meter container ext3 jbd mbcache usbhid hid ttm drm_kms_helper drm i2c_algo_bit sysimgblt sysfillrect i2c_core syscopyarea ehci_hcd usbcore usb_co mmon sd_mod crc_t10dif processor thermal_sys hwmon scsi_dh_rdac scsi_dh_emc scsi_dh_hp_sw scsi_dh_alua scsi_dh ahci libahci libata mpt3sas(EX) configfs scsi_transport_sas raid_c lass scsi_mod [last unloaded: witdriver] [ 948.894346] Supported: No, Unsupported modules are loaded [ 948.894348] [ 948.894350] Pid: 31427, comm: nginx Tainted: G ENX 3.0.101-0.47.52-default #1 ZTE Grantley/S1008 [ 948.894354] RIP: 0010:[<ffffffff81133662>] [<ffffffff81133662>] valid_swaphandles+0x72/0x150 [ 948.894357] RSP: 0000:ffff883e4b021ca8 EFLAGS: 00010216 [ 948.894359] RAX: 0000000000000008 RBX: 00181818182f98a0 RCX: 0000000000000003 [ 948.894362] RDX: 000000000000408e RSI: 0000000000000000 RDI: ffffffff81e56ce0 [ 948.894364] RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000029 [ 948.894366] R10: ffff883e4b011218 R11: ffff883e4dac4bc0 R12: 00181818182f9898 [ 948.894368] R13: 00181818182f989a R14: 0000000000000000 R15: ffff883e4b021d30 [ 948.894371] FS: 00007f1c66ca7720(0000) GS:ffff88407dda0000(0000) knlGS:0000000000000000 [ 948.894373] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b [ 948.894375] CR2: 000000000000000c CR3: 0000003e4b006000 CR4: 00000000001407e0 [ 948.894377] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 948.894380] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 [ 948.894382] Process nginx (pid: 31427, threadinfo ffff883e4b020000, task ffff883e4b01e540) [ 948.894384] Stack: [ 948.894385] ffff883e4b021cc4 30181818182f989a 0000000000000000 00007f1ac86072fc [ 948.894391] ffff883f89f0c038 ffff883fbe860d78 00000000000200da ffffffff81132bd6 [ 948.894397] 0000000000000000 30181818182f989a 0000000000000000 0000000000000000 [ 948.894401] Call Trace: [ 948.894411] [<ffffffff81132bd6>] swapin_readahead+0x26/0xd0 [ 948.894417] [<ffffffff81122a8d>] do_swap_page+0xed/0x5f0 [ 948.894422] [<ffffffff81123ab1>] handle_pte_fault+0x1e1/0x230 [ 948.894429] [<ffffffff8146873d>] do_page_fault+0x1fd/0x4c0 [ 948.894434] [<ffffffff81465345>] page_fault+0x25/0x30 [ 948.894440] [<00007f1c65877dab>] 0x7f1c65877daa [ 948.894441] Code: ff ff ff ff 01 49 21 c5 4c 89 eb 48 d3 eb 48 d3 e3 48 85 db 4c 0f 45 e3 e8 cc 15 33 00 b8 01 00 00 00 89 e9 d3 e0 48 98 48 01 c3 [ 948.894455] 8b 46 0c 48 39 c3 48 89 c7 49 8d 45 01 48 0f 46 fb 48 39 f8 [ 948.894462] RIP [<ffffffff81133662>] valid_swaphandles+0x72/0x150 [ 948.894465] RSP <ffff883e4b021ca8> [ 948.894467] CR2: 000000000000000c We also collect vmcore. crash> dis -l valid_swaphandles+0x72 /home/chengry/linux-3.0.101-0.47.52/mm/swapfile.c: 2318 0xffffffff81133662 <valid_swaphandles+114>: mov 0xc(%r14),%eax crash> dis -l valid_swaphandles /home/chengry/linux-3.0.101-0.47.52/mm/swapfile.c: 2305 0xffffffff811335f0 <valid_swaphandles>: push %r15 0xffffffff811335f2 <valid_swaphandles+2>: mov %rsi,%r15 /home/chengry/linux-3.0.101-0.47.52/mm/swapfile.c: 2312 0xffffffff811335f5 <valid_swaphandles+5>: xor %esi,%esi /home/chengry/linux-3.0.101-0.47.52/mm/swapfile.c: 2305 0xffffffff811335f7 <valid_swaphandles+7>: push %r14 0xffffffff811335f9 <valid_swaphandles+9>: push %r13 0xffffffff811335fb <valid_swaphandles+11>: push %r12 0xffffffff811335fd <valid_swaphandles+13>: push %rbp 0xffffffff811335fe <valid_swaphandles+14>: push %rbx 0xffffffff811335ff <valid_swaphandles+15>: sub $0x8,%rsp /home/chengry/linux-3.0.101-0.47.52/mm/swapfile.c: 2307 0xffffffff81133603 <valid_swaphandles+19>: mov 0xd233c3(%rip),%ebp # 0xffffffff81e569cc /home/chengry/linux-3.0.101-0.47.52/mm/swapfile.c: 2312 0xffffffff81133609 <valid_swaphandles+25>: test %ebp,%ebp 0xffffffff8113360b <valid_swaphandles+27>: je 0xffffffff81133723 <valid_swaphandles+307> /home/chengry/linux-3.0.101-0.47.52/mm/swapfile.c: 2315 0xffffffff81133611 <valid_swaphandles+33>: mov %rdi,%rax /home/chengry/linux-3.0.101-0.47.52/include/linux/swapops.h: 49 0xffffffff81133614 <valid_swaphandles+36>: mov %rdi,%r13 /home/chengry/linux-3.0.101-0.47.52/mm/swapfile.c: 2317 0xffffffff81133617 <valid_swaphandles+39>: mov %ebp,%ecx /home/chengry/linux-3.0.101-0.47.52/mm/swapfile.c: 2315 0xffffffff81133619 <valid_swaphandles+41>: shr $0x39,%rax /home/chengry/linux-3.0.101-0.47.52/include/linux/spinlock.h: 293 0xffffffff8113361d <valid_swaphandles+45>: mov $0xffffffff81e56ce0,%rdi /home/chengry/linux-3.0.101-0.47.52/mm/swapfile.c: 2319 0xffffffff81133624 <valid_swaphandles+52>: mov $0x1,%r12d /home/chengry/linux-3.0.101-0.47.52/mm/swapfile.c: 2315 0xffffffff8113362a <valid_swaphandles+58>: mov -0x7e1a9300(,%rax,8),%r14 /home/chengry/linux-3.0.101-0.47.52/include/linux/swapops.h: 49 0xffffffff81133632 <valid_swaphandles+66>: movabs $0x1ffffffffffffff,%rax 0xffffffff8113363c <valid_swaphandles+76>: and %rax,%r13 /home/chengry/linux-3.0.101-0.47.52/mm/swapfile.c: 2317 0xffffffff8113363f <valid_swaphandles+79>: mov %r13,%rbx 0xffffffff81133642 <valid_swaphandles+82>: shr %cl,%rbx 0xffffffff81133645 <valid_swaphandles+85>: shl %cl,%rbx /home/chengry/linux-3.0.101-0.47.52/mm/swapfile.c: 2319 0xffffffff81133648 <valid_swaphandles+88>: test %rbx,%rbx 0xffffffff8113364b <valid_swaphandles+91>: cmovne %rbx,%r12 /home/chengry/linux-3.0.101-0.47.52/include/linux/spinlock.h: 293 0xffffffff8113364f <valid_swaphandles+95>: callq 0xffffffff81464c20 <_raw_spin_lock> /home/chengry/linux-3.0.101-0.47.52/mm/swapfile.c: 2318 0xffffffff81133654 <valid_swaphandles+100>: mov $0x1,%eax 0xffffffff81133659 <valid_swaphandles+105>: mov %ebp,%ecx 0xffffffff8113365b <valid_swaphandles+107>: shl %cl,%eax 0xffffffff8113365d <valid_swaphandles+109>: cltq 0xffffffff8113365f <valid_swaphandles+111>: add %rax,%rbx 0xffffffff81133662 <valid_swaphandles+114>: mov 0xc(%r14),%eax 0xffffffff81133666 <valid_swaphandles+118>: cmp %rax,%rbx 0xffffffff81133669 <valid_swaphandles+121>: mov %rax,%rdi /home/chengry/linux-3.0.101-0.47.52/mm/swapfile.c: 2331 0xffffffff8113366c <valid_swaphandles+124>: lea 0x1(%r13),%rax /home/chengry/linux-3.0.101-0.47.52/mm/swapfile.c: 2318 0xffffffff81133670 <valid_swaphandles+128>: cmovbe %rbx,%rdi /home/chengry/linux-3.0.101-0.47.52/mm/swapfile.c: 2331 0xffffffff81133674 <valid_swaphandles+132>: cmp %rdi,%rax 0xffffffff81133677 <valid_swaphandles+135>: jae 0xffffffff81133734 <valid_swaphandles+324> /home/chengry/linux-3.0.101-0.47.52/mm/swapfile.c: 2333 0xffffffff8113367d <valid_swaphandles+141>: mov 0x10(%r14),%rcx 0xffffffff81133681 <valid_swaphandles+145>: movzbl 0x1(%rcx,%r13,1),%edx 0xffffffff81133687 <valid_swaphandles+151>: test %dl,%dl 0xffffffff81133689 <valid_swaphandles+153>: je 0xffffffff81133734 <valid_swaphandles+324> /home/chengry/linux-3.0.101-0.47.52/mm/swapfile.c: 2335 0xffffffff8113368f <valid_swaphandles+159>: and $0xffffffbf,%edx 0xffffffff81133692 <valid_swaphandles+162>: cmp $0x3f,%dl 0xffffffff81133695 <valid_swaphandles+165>: je 0xffffffff81133734 <valid_swaphandles+324> 0xffffffff8113369b <valid_swaphandles+171>: add %r13,%rcx 0xffffffff8113369e <valid_swaphandles+174>: xor %esi,%esi 0xffffffff811336a0 <valid_swaphandles+176>: jmp 0xffffffff811336bc <valid_swaphandles+204> 0xffffffff811336a2 <valid_swaphandles+178>: nopw 0x0(%rax,%rax,1) /home/chengry/linux-3.0.101-0.47.52/mm/swapfile.c: 2333 0xffffffff811336a8 <valid_swaphandles+184>: movzbl 0x2(%rcx),%edx 0xffffffff811336ac <valid_swaphandles+188>: test %dl,%dl 0xffffffff811336ae <valid_swaphandles+190>: je 0xffffffff811336c8 <valid_swaphandles+216> and the source code should be： int valid_swaphandles(swp_entry_t entry, unsigned long *offset) { struct swap_info_struct *si; int our_page_cluster = page_cluster; pgoff_t target, toff; pgoff_t base, end; int nr_pages = 0; if (!our_page_cluster) /* no readahead */ return 0; si = swap_info[swp_type(entry)]; target = swp_offset(entry); base = (target >> our_page_cluster) << our_page_cluster; end = base + (1 << our_page_cluster); if (!base) /* first page is swap header */ base++; spin_lock(&swap_lock); if (frontswap_test(si, target)) { spin_unlock(&swap_lock); return 0; } if (end > si->max) /* don't go beyond end of map */ end = si->max; it means that we get （swap_info_struct si ） is null。 and i get the related value ： crash> p swap_info swap_info = $11 = {0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0} crash> p swap_list swap_list = $14 = { head = -1, next = -1 } crash> p nr_swapfiles nr_swapfiles = $17 = 0 crash> p total_swap_pages total_swap_pages = $19 = 0 crash> p least_priority least_priority = $20 = 0 crash> p nr_swap_pages nr_swap_pages = $7 = 0 crash> p vm_swappiness vm_swappiness = $8 = 0 crash> p min_free_kbytes min_free_kbytes = $9 = 2048000 crash> kmem -i PAGES TOTAL PERCENTAGE TOTAL MEM 65934474 251.5 GB ---- FREE 28076248 107.1 GB 42% of TOTAL MEM USED 37858226 144.4 GB 57% of TOTAL MEM SHARED 2194009 8.4 GB 3% of TOTAL MEM BUFFERS 16214 63.3 MB 0% of TOTAL MEM CACHED 24341721 92.9 GB 36% of TOTAL MEM SLAB 1415022 5.4 GB 2% of TOTAL MEM TOTAL SWAP 0 0 ---- SWAP USED 0 0 100% of TOTAL SWAP SWAP FREE 0 0 0% of TOTAL SWAP
#5 [ffff883e4b021bf0] page_fault at ffffffff81465345
[exception RIP: valid_swaphandles+114]
RIP: ffffffff81133662 RSP: ffff883e4b021ca8 RFLAGS: 00010216
RAX: 0000000000000008 RBX: 00181818182f98a0 RCX: 0000000000000003
RDX: 000000000000408e RSI: 0000000000000000 RDI: ffffffff81e56ce0
RBP: 0000000000000003 R8: 0000000000000000 R9: 0000000000000029
R10: ffff883e4b011218 R11: ffff883e4dac4bc0 R12: 00181818182f9898
R13: 00181818182f989a R14: 0000000000000000 R15: ffff883e4b021d30
ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0000
ffff883e4b021bf8: ffff883e4b021d30 0000000000000000
ffff883e4b021c08: 00181818182f989a 00181818182f9898
ffff883e4b021c18: 0000000000000003 00181818182f98a0
ffff883e4b021c28: ffff883e4dac4bc0 ffff883e4b011218
ffff883e4b021c38: 0000000000000029 0000000000000000
ffff883e4b021c48: 0000000000000008 0000000000000003
ffff883e4b021c58: 000000000000408e 0000000000000000
ffff883e4b021c68: ffffffff81e56ce0 ffffffffffffffff
ffff883e4b021c78: ffffffff81133662 0000000000000010
ffff883e4b021c88: 0000000000010216 ffff883e4b021ca8
ffff883e4b021c98: 0000000000000000 ffffffff81133654
ffff883e4b021ca8: ffff883e4b021cc4 30181818182f989a
ffff883e4b021cb8: 0000000000000000 00007f1ac86072fc
ffff883e4b021cc8: ffff883f89f0c038 ffff883fbe860d78
ffff883e4b021cd8: 00000000000200da ffffffff81132bd6
#6 [ffff883e4b021ce0] swapin_readahead at ffffffff81132bd6
ffff883e4b021ce8: 0000000000000000 30181818182f989a
ffff883e4b021cf8: 0000000000000000 0000000000000000
ffff883e4b021d08: 0000000000000000 ffffffff81257735
ffff883e4b021d18: 0000000000000000 ffffffff8146508e
ffff883e4b021d28: ffff88407ddb3a20 ffff881fcf625800
ffff883e4b021d38: ffffffff81103809 30181818182f989a
ffff883e4b021d48: 0000000000000000 0000000000000000
ffff883e4b021d58: ffff883f89f0c038 0000000000000029
ffff883e4b021d68: ffff883e4dac4bc0 ffffffff81122a8d
#7 [ffff883e4b021d70] do_swap_page at ffffffff81122a8d
ffff883e4b021d78: ffff883e4dac4bc0 ffff883e4b011218
ffff883e4b021d88: ffff883e4b011218 00007f1ac86072fc
ffff883e4b021d98: ffff883fbe860d78 ffff883f89f0c038
ffff883e4b021da8: ffffea00de62cab0 ffff883fbe860d78
ffff883e4b021db8: ffffea00de62cab0 303030305f313430
ffff883e4b021dc8: 0000000000000000 ffff883fbe860d78
ffff883e4b021dd8: ffff883f89f0c038 0000000000000029
ffff883e4b021de8: 00007f1ac86072fc ffffffff81123ab1
#8 [ffff883e4b021df0] handle_pte_fault at ffffffff81123ab1
ffff883e4b021df8: 303030305f313430 ffffffff81123b52 --303030305f313430 orig_pte should be
ffff883e4b021e08: 000000014b011218 ffff880000000358
ffff883e4b021e18: 00000029de62caa0 ffff883fbe860d78
ffff883e4b021e28: 00007f1ac86072fc 0000000000000006
ffff883e4b021e38: ffff883e4b021f58 0000000000000029
ffff883e4b021e48: ffff883e4dac4bc0 ffffffff8146873d
#9 [ffff883e4b021e50] do_page_fault at ffffffff8146873d
ffff883e4b021e58: ffff883e4dac4c20 ffff883e4b01e540
ffff883e4b021e68: ffff883e4b021fd8 ffff883e4b021fd8
ffff883e4b021e78: 0000000000010900 ffff883e4b01e540
ffff883e4b021e88: ffff883e4dd18480 ffff883e4b01e540
ffff883e4b021e98: ffffffff81055e30 dead000000100100
ffff883e4b021ea8: dead000000200200 ffffffff8146da6e
ffff883e4b021eb8: ffff883e4b021f70 ffffffff8146508e
ffff883e4b021ec8: 00000000000006fe ffffffff8146da6e
ffff883e4b021ed8: ffff883e4dac4bc0 ffff883e4b011218
ffff883e4b021ee8: 0000000000000029 0000000000000001
ffff883e4b021ef8: 0000000000000000 0000000400000063
ffff883e4b021f08: 0000000000000001 00007f1ac86072fc
we have a lots of free memory，and i set the nr_swapfiles be zero when the machine start，although i know that nr_swapfiles be 0 is not mean we close the swap ,but i still be refused why the machine should be swap now ? and why i get NULL pointer? i didn't set the swap partition enable。