Subject: Re: [RESEND] Soft lockup after huge page offline attempt

From: Michael Neuling <[email-masked]>
Date: Wed, 02 Sep 2015 20:20:21 +1000

On Wed, 2015-09-02 at 15:37 +0530, Anshuman Khandual wrote:
> Hello,
> 
> Worked on a modified version of the following selftest
> test case in the kernel source.
> 
> tools/testing/selftests/vm/hugepage-mmap.c

Please send the test case and how to run it here.

Mikey

> This modified test will try to do the following sequence of
> events in the same order.
> 
> (1) Allocate 16 Huge TLB pages (16MB each) through mmap
> 
> (2) mlock() the entire range of 256MB memory
> 
> (3) Fetch PFN from /proc/self/pagemap for each huge TLB page
>     starting address present in the 256MB range
> 
> (4) Convert each PFN into PA as PFN << PAGE_SHIFT which is then
>     written into /sys/devices/system/memory/soft_offline_page
> 
> (5) unmap() the 256MB memory range
> 
> (6) unlink() the file (inside the hugetlbfs mount path) used for mmap
> 
> The soft offline page attempts fail as expected as we dont support that on
> POWER yet.
> 
> [  145.359405] soft offline: 0xba100: migration failed 1, type 43ffff000004008
> [  145.359572] soft offline: 0xba200: migration failed 1, type 43ffff000004008
> [  145.359644] soft offline: 0xba300: migration failed 1, type 43ffff000004008
> [  145.359716] soft offline: 0xba400: migration failed 1, type 43ffff000004008
> [  145.359783] soft offline: 0xba500: migration failed 1, type 43ffff000004008
> [  145.359853] soft offline: 0xba600: migration failed 1, type 43ffff000004008
> [  145.359931] soft offline: 0xba700: migration failed 1, type 43ffff000004008
> [  145.360008] soft offline: 0xba800: migration failed 1, type 43ffff000004008
> [  145.360080] soft offline: 0xba900: migration failed 1, type 43ffff000004008
> [  145.360148] soft offline: 0xbaa00: migration failed 1, type 43ffff000004008
> [  145.360218] soft offline: 0xbab00: migration failed 1, type 43ffff000004008
> [  145.360286] soft offline: 0xbac00: migration failed 1, type 43ffff000004008
> [  145.360353] soft offline: 0xbad00: migration failed 1, type 43ffff000004008
> [  145.360420] soft offline: 0xbae00: migration failed 1, type 43ffff000004008
> [  145.360485] soft offline: 0xbaf00: migration failed 1, type 43ffff000004008
> [  145.360552] soft offline: 0xbb000: migration failed 1, type 43ffff000004008
> 
> But interestingly the test thread hangs for good after that. We can see this
> soft lock up message in the console.
> 
> [  168.038353] NMI watchdog: BUG: soft lockup - CPU#3 stuck for 22s! [hugepage-mmap:1238]
> [  168.038384] Modules linked in: windfarm_smu_sat i2c_core pseries_rng windfarm_pid xfs libcrc32c ibmvscsi scsi_transport_srp ibmveth
> [  168.038411] CPU: 3 PID: 1238 Comm: hugepage-mmap Not tainted 4.2.0+ #7
> [  168.038416] task: c0000000ffa304b0 ti: c000000beff8c000 task.ti: c000000beff8c000
> [  168.038422] NIP: c000000000228164 LR: c00000000022820c CTR: c0000000003ff060
> [  168.038428] REGS: c000000beff8f8c0 TRAP: 0901   Not tainted  (4.2.0+)
> [  168.038432] MSR: 8000000000009033 <SF,EE,ME,IR,DR,RI,LE>  CR: 22000228  XER: 00000000
> [  168.038446] CFAR: c000000000228180 SOFTE: 1 
> GPR00: 0000000000000000 c000000beff8fb40 c000000001306000 f000000002e84000 
> GPR04: c000000beff8fb60 0000000000000220 c000000bf98b5248 0000000000000000 
> GPR08: 0000000000000044 0000000000000000 f000000002e8401c 0000000000000000 
> GPR12: 0000000000000000 c00000000ea51c80 
> [  168.038483] NIP [c000000000228164] find_get_pages+0xa4/0x1e0
> [  168.038489] LR [c00000000022820c] find_get_pages+0x14c/0x1e0
> [  168.038493] Call Trace:
> [  168.038496] [c000000beff8fb40] [c000000beff8fbc0] 0xc000000beff8fbc0 (unreliable)
> [  168.038503] [c000000beff8fbc0] [c00000000023ba20] pagevec_lookup+0x50/0x80
> [  168.038510] [c000000beff8fc00] [c0000000003fe630] truncate_hugepages+0xb0/0x280
> [  168.038517] [c000000beff8fd10] [c0000000003ff090] hugetlbfs_evict_inode+0x30/0x70
> [  168.038524] [c000000beff8fd40] [c0000000002f1d34] evict+0xf4/0x290
> [  168.038531] [c000000beff8fd80] [c0000000002e3268] do_unlinkat+0x208/0x370
> [  168.038538] [c000000beff8fe30] [c000000000009360] system_call+0x38/0xd0
> [  168.038543] Instruction dump:
> [  168.038546] 419e00c8 e87f0000 2fa30000 419e0080 786907a1 408200d8 813b000c 552902ee 
> [  168.038556] 0b090000 3943001c 7c2004ac 7d205028 <2c090000> 41c20014 31090001 7d00512d 
> 
> After a while, we see these messages as well on the console before it freezes.
> 
> INFO: rcu_sched self-detected stall on CPU
> [  205.368370] 	3: (5999 ticks this GP) idle=b23/140000000000001/0 softirq=1329/1329 fqs=6000 
> [  205.368375] 	 (t=6000 jiffies g=896 c=895 q=678)
> [  205.368383] Task dump for CPU 3:
> [  205.368387] hugepage-mmap   R  running task        0  1238   1233 0x00042004
> [  205.368394] Call Trace:
> [  205.368401] [c000000beff8f3e0] [c000000000106660] sched_show_task+0xe0/0x180 (unreliable)
> [  205.368409] [c000000beff8f450] [c00000000014d9e4] rcu_dump_cpu_stacks+0xe4/0x150
> [  205.368416] [c000000beff8f4a0] [c0000000001529c4] rcu_check_callbacks+0x6b4/0x9b0
> [  205.368424] [c000000beff8f5d0] [c000000000159ee4] update_process_times+0x54/0xa0
> [  205.368431] [c000000beff8f600] [c000000000170b48] tick_sched_handle.isra.6+0x48/0xe0
> [  205.368437] [c000000beff8f640] [c000000000170c44] tick_sched_timer+0x64/0xd0
> [  205.368444] [c000000beff8f680] [c00000000015a954] __hrtimer_run_queues+0x124/0x3c0
> [  205.368450] [c000000beff8f710] [c00000000015b88c] hrtimer_interrupt+0xec/0x2c0
> [  205.368457] [c000000beff8f7d0] [c00000000001f77c] __timer_interrupt+0x8c/0x230
> [  205.368464] [c000000beff8f820] [c00000000001fe30] timer_interrupt+0xa0/0xe0
> [  205.368470] [c000000beff8f850] [c000000000002768] decrementer_common+0x168/0x180
> [  205.368478] --- interrupt: 901 at find_get_pages+0xa0/0x1e0
> [  205.368478]     LR = find_get_pages+0x14c/0x1e0
> [  205.368486] [c000000beff8fb40] [c000000beff8fbc0] 0xc000000beff8fbc0 (unreliable)
> [  205.368493] [c000000beff8fbc0] [c00000000023ba20] pagevec_lookup+0x50/0x80
> [  205.368500] [c000000beff8fc00] [c0000000003fe630] truncate_hugepages+0xb0/0x280
> [  205.368507] [c000000beff8fd10] [c0000000003ff090] hugetlbfs_evict_inode+0x30/0x70
> [  205.368513] [c000000beff8fd40] [c0000000002f1d34] evict+0xf4/0x290
> [  205.368520] [c000000beff8fd80] [c0000000002e3268] do_unlinkat+0x208/0x370
> [  205.368526] [c000000beff8fe30] [c000000000009360] system_call+0x38/0xd0
> 
> 
> Then the entire system hangs for good, requiring a reboot. The problem can be recreated
> without unlink() step if we just try to unmount the hugetlbfs afterwards. I am still
> looking into this problem. Please do let me know if you have any suggestions/thoughts
> or comments about this issue.
> 
> Regards
> Anshuman
>