Eric Wheeler wrote: > I just tried v4.9.78 and we still get the deadlock. I've backported your > MemAlloc timing patch and yout timing is included in the output. Both > full sysrq traces (30 seconds apart) are available here and I made sure it > includes both "Showing busy workqueues and worker pools" sections: > > https://www.linuxglobal.com/static/2018-01-27-hv1-deadlock-v4.9.78 > > # ps -eo pid,lstart,cmd,stat |grep D > PID STARTED CMD STAT > 16127 Sat Jan 27 05:24:29 2018 crm_node -N 2 D << Both in D state > 22444 Sat Jan 27 05:39:50 2018 rsync --server --sender -vl DNs << Both in D state > Thank you. Although the capture is still incomplete, I noticed that there was a surprising entry. crm_node was stalling at page fault for 33950 seconds! That is, crm_node already started stalling at uptime = 45375. ---------- [79325.124062] MemAlloc: crm_node(16127) flags=0xc00900 switches=10 seq=441 gfp=0x24200ca(GFP_HIGHUSER_MOVABLE) order=0 delay=33950065 uninterruptible [79325.125113] ffff8cf6d750dd00 0000000000000000 ffff8cf74b9d5800 ffff8cf76fd19940 [79325.125684] ffff8cf6c3d84200 ffffada2a17af6c8 ffffffff8e7178f5 0000000000000000 [79325.126245] 0000000000000000 0000000000000000 ffff8cf6c3d84200 7fffffffffffffff [79325.126800] Call Trace: [79325.127339] [<ffffffff8e7178f5>] ? __schedule+0x195/0x630 [79325.127985] [<ffffffff8e718630>] ? bit_wait+0x50/0x50 [79325.128519] [<ffffffff8e717dc6>] schedule+0x36/0x80 [79325.129040] [<ffffffff8e71afa6>] schedule_timeout+0x1e6/0x320 [79325.129560] [<ffffffff8e718630>] ? bit_wait+0x50/0x50 [79325.130100] [<ffffffff8e7176f6>] io_schedule_timeout+0xa6/0x110 [79325.130683] [<ffffffff8e71864b>] bit_wait_io+0x1b/0x60 [79325.131199] [<ffffffff8e718286>] __wait_on_bit_lock+0x86/0xd0 [79325.131723] [<ffffffff8e1acb22>] __lock_page+0x82/0xb0 [79325.132238] [<ffffffff8e0e9e00>] ? autoremove_wake_function+0x40/0x40 [79325.132765] [<ffffffff8e1ae63b>] pagecache_get_page+0x16b/0x230 [79325.133284] [<ffffffff8e1ca3da>] shmem_unused_huge_shrink+0x28a/0x330 [79325.133814] [<ffffffff8e1ca4a7>] shmem_unused_huge_scan+0x27/0x30 [79325.134338] [<ffffffff8e23f941>] super_cache_scan+0x181/0x190 [79325.134875] [<ffffffff8e1c1ab1>] shrink_slab+0x261/0x470 [79325.135386] [<ffffffff8e1c6588>] shrink_node+0x108/0x310 [79325.135904] [<ffffffff8e1c6927>] node_reclaim+0x197/0x210 [79325.136458] [<ffffffff8e1b5dd8>] get_page_from_freelist+0x168/0x9f0 [79325.137023] [<ffffffff8e1adc8e>] ? find_get_entry+0x1e/0x100 [79325.137560] [<ffffffff8e1ca9c5>] ? shmem_getpage_gfp+0xf5/0xbb0 [79325.138061] [<ffffffff8e1b77ae>] __alloc_pages_nodemask+0x10e/0x2d0 [79325.138619] [<ffffffff8e207d08>] alloc_pages_current+0x88/0x120 [79325.139117] [<ffffffff8e070287>] pte_alloc_one+0x17/0x40 [79325.139626] [<ffffffff8e1e117e>] __pte_alloc+0x1e/0x100 [79325.140138] [<ffffffff8e1e3622>] alloc_set_pte+0x4f2/0x560 [79325.140698] [<ffffffff8e1e3770>] do_fault+0xe0/0x620 [79325.141168] [<ffffffff8e1e5504>] handle_mm_fault+0x644/0xdd0 [79325.141667] [<ffffffff8e06a96e>] __do_page_fault+0x25e/0x4f0 [79325.142163] [<ffffffff8e06ac30>] do_page_fault+0x30/0x80 [79325.142660] [<ffffffff8e003b55>] ? do_syscall_64+0x175/0x180 [79325.143132] [<ffffffff8e71dae8>] page_fault+0x28/0x30 ---------- You took SysRq-t after multiple processes (in this case, crm_node and rsync) got stuck, didn't you? I feel anxious about LIST_POISON1 (dead000000000100) and LIST_POISON2 (dead000000000200) are showing up at rsync side. ---------- [79325.156361] rsync D 0 22444 22441 0x00000080 [79325.156871] ffff8cf3b8437440 0000000000000000 ffff8cf74b9d1600 ffff8cf76fc59940 [79325.157307] ffff8cf3eef74200 ffffada2a0e17b18 ffffffff8e7178f5 dead000000000100 [79325.157764] dead000000000200 ffff8cf6db9101a8 ffff8cf3eef74200 7fffffffffffffff [79325.158225] Call Trace: [79325.158690] [<ffffffff8e7178f5>] ? __schedule+0x195/0x630 [79325.159142] [<ffffffff8e718630>] ? bit_wait+0x50/0x50 [79325.159604] [<ffffffff8e717dc6>] schedule+0x36/0x80 [79325.160053] [<ffffffff8e71afa6>] schedule_timeout+0x1e6/0x320 [79325.160536] [<ffffffff8e0de21c>] ? enqueue_entity+0x3bc/0x570 [79325.160984] [<ffffffff8e11bf5b>] ? ktime_get+0x3b/0xb0 [79325.161450] [<ffffffff8e718630>] ? bit_wait+0x50/0x50 [79325.161891] [<ffffffff8e7176f6>] io_schedule_timeout+0xa6/0x110 [79325.162337] [<ffffffff8e71864b>] bit_wait_io+0x1b/0x60 [79325.162787] [<ffffffff8e718286>] __wait_on_bit_lock+0x86/0xd0 [79325.163231] [<ffffffff8e1acb22>] __lock_page+0x82/0xb0 [79325.163681] [<ffffffff8e0e9e00>] ? autoremove_wake_function+0x40/0x40 [79325.164133] [<ffffffff8e1addd1>] find_lock_entry+0x61/0x80 [79325.164597] [<ffffffff8e1ca9c5>] shmem_getpage_gfp+0xf5/0xbb0 [79325.165053] [<ffffffff8e1cb9b9>] shmem_file_read_iter+0x159/0x310 [79325.165516] [<ffffffff8e23b2ff>] __vfs_read+0xdf/0x130 [79325.165966] [<ffffffff8e23ba2c>] vfs_read+0x8c/0x130 [79325.166430] [<ffffffff8e23cf95>] SyS_read+0x55/0xc0 [79325.166865] [<ffffffff8e003a47>] do_syscall_64+0x67/0x180 [79325.167292] [<ffffffff8e71c530>] entry_SYSCALL64_slow_path+0x25/0x25 ---------- > > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > crm_node D 0 16127 16126 0x00000080 > MemAlloc: crm_node(16127) flags=0xc00900 switches=10 seq=441 gfp=0x24200ca(GFP_HIGHUSER_MOVABLE) order=0 delay=209469 uninterruptible At this point, crm_node already stalled for 209 seconds. Since switches= and seq= did not change until you took SysRq-t, crm_node kept sleeping. > ffff8cf6d750dd00 0000000000000000 ffff8cf74b9d5800 ffff8cf76fd19940 > ffff8cf6c3d84200 ffffada2a17af6c8 ffffffff8e7178f5 0000000000000000 > 0000000000000000 0000000000000000 ffff8cf6c3d84200 7fffffffffffffff > Call Trace: > [<ffffffff8e7178f5>] ? __schedule+0x195/0x630 > [<ffffffff8e718630>] ? bit_wait+0x50/0x50 > [<ffffffff8e717dc6>] schedule+0x36/0x80 > [<ffffffff8e71afa6>] schedule_timeout+0x1e6/0x320 > [<ffffffff8e718630>] ? bit_wait+0x50/0x50 > [<ffffffff8e7176f6>] io_schedule_timeout+0xa6/0x110 > [<ffffffff8e71864b>] bit_wait_io+0x1b/0x60 > [<ffffffff8e718286>] __wait_on_bit_lock+0x86/0xd0 > [<ffffffff8e1acb22>] __lock_page+0x82/0xb0 > [<ffffffff8e0e9e00>] ? autoremove_wake_function+0x40/0x40 > [<ffffffff8e1ae63b>] pagecache_get_page+0x16b/0x230 > [<ffffffff8e1ca3da>] shmem_unused_huge_shrink+0x28a/0x330 > [<ffffffff8e1ca4a7>] shmem_unused_huge_scan+0x27/0x30 > [<ffffffff8e23f941>] super_cache_scan+0x181/0x190 > [<ffffffff8e1c1ab1>] shrink_slab+0x261/0x470 > [<ffffffff8e1c6588>] shrink_node+0x108/0x310 > [<ffffffff8e1c6927>] node_reclaim+0x197/0x210 > [<ffffffff8e1b5dd8>] get_page_from_freelist+0x168/0x9f0 > [<ffffffff8e1adc8e>] ? find_get_entry+0x1e/0x100 > [<ffffffff8e1ca9c5>] ? shmem_getpage_gfp+0xf5/0xbb0 > [<ffffffff8e1b77ae>] __alloc_pages_nodemask+0x10e/0x2d0 > [<ffffffff8e207d08>] alloc_pages_current+0x88/0x120 > [<ffffffff8e070287>] pte_alloc_one+0x17/0x40 > [<ffffffff8e1e117e>] __pte_alloc+0x1e/0x100 > [<ffffffff8e1e3622>] alloc_set_pte+0x4f2/0x560 > [<ffffffff8e1e3770>] do_fault+0xe0/0x620 > [<ffffffff8e1e5504>] handle_mm_fault+0x644/0xdd0 > [<ffffffff8e06a96e>] __do_page_fault+0x25e/0x4f0 > [<ffffffff8e06ac30>] do_page_fault+0x30/0x80 > [<ffffffff8e003b55>] ? do_syscall_64+0x175/0x180 > [<ffffffff8e71dae8>] page_fault+0x28/0x30 > > Pid 22444 didn't show up in the hung_task warning like crm_node did, > but its /proc/pid/stack looks like so: > > ~]# cat /proc/22444/stack > [<ffffffff8e1acb22>] __lock_page+0x82/0xb0 > [<ffffffff8e1addd1>] find_lock_entry+0x61/0x80 > [<ffffffff8e1ca9c5>] shmem_getpage_gfp+0xf5/0xbb0 > [<ffffffff8e1cb9b9>] shmem_file_read_iter+0x159/0x310 > [<ffffffff8e23b2ff>] __vfs_read+0xdf/0x130 > [<ffffffff8e23ba2c>] vfs_read+0x8c/0x130 > [<ffffffff8e23cf95>] SyS_read+0x55/0xc0 > [<ffffffff8e003a47>] do_syscall_64+0x67/0x180 > [<ffffffff8e71c530>] entry_SYSCALL64_slow_path+0x25/0x25 > [<ffffffffffffffff>] 0xffffffffffffffff I guess that /proc/sys/kernel/hung_task_warnings already became 0. Since the default value of /proc/sys/kernel/hung_task_warnings is 10, only first 10 warnings are shown. You can set -1 to /proc/sys/kernel/hung_task_warnings so that all hung_task warnings are shown. > > > ==================== 4.14.15 ==================== > > On the other server running 4.14.15 the stacks look the same as you've > seen before. Both full sysrq traces (30 seconds apart) are available here > and I made sure it includes both "Showing busy workqueues and worker > pools" sections: > > https://www.linuxglobal.com/static/2018-01-28-hv2-deadlock-v4.14.15 > > ~]# ps -eo pid,lstart,cmd,stat |grep D > PID STARTED CMD STAT > 27163 Sat Jan 27 05:15:48 2018 crm_node -N 2 D > 1125 Sat Jan 27 14:34:40 2018 /usr/sbin/libvirtd D > crm_node was stalling at page fault for 119634 seconds (more than one day)! ---------- crm_node D 0 27163 1 0x00000084 MemAlloc: crm_node(27163) flags=0xc00900 switches=3 seq=438 gfp=0x14200ca(GFP_HIGHUSER_MOVABLE) order=0 delay=119634513 uninterruptible Call Trace: ? __schedule+0x1dc/0x770 schedule+0x32/0x80 io_schedule+0x12/0x40 __lock_page+0x105/0x150 ? page_cache_tree_insert+0xb0/0xb0 pagecache_get_page+0x161/0x210 shmem_unused_huge_shrink+0x334/0x3f0 super_cache_scan+0x176/0x180 shrink_slab+0x275/0x460 shrink_node+0x10e/0x320 node_reclaim+0x19d/0x250 get_page_from_freelist+0x16a/0xac0 ? radix_tree_lookup_slot+0x1e/0x50 ? find_lock_entry+0x45/0x80 ? shmem_getpage_gfp.isra.34+0xe5/0xc80 __alloc_pages_nodemask+0x111/0x2c0 pte_alloc_one+0x13/0x40 __pte_alloc+0x19/0x100 alloc_set_pte+0x468/0x4c0 finish_fault+0x3a/0x70 __handle_mm_fault+0x94a/0x1190 handle_mm_fault+0xf2/0x210 __do_page_fault+0x253/0x4d0 do_page_fault+0x33/0x120 ? page_fault+0x36/0x60 page_fault+0x4c/0x60 crm_node D 0 27163 1 0x00000084 MemAlloc: crm_node(27163) flags=0xc00900 switches=3 seq=438 gfp=0x14200ca(GFP_HIGHUSER_MOVABLE) order=0 delay=119682540 uninterruptible Call Trace: ? __schedule+0x1dc/0x770 schedule+0x32/0x80 io_schedule+0x12/0x40 __lock_page+0x105/0x150 ? page_cache_tree_insert+0xb0/0xb0 pagecache_get_page+0x161/0x210 shmem_unused_huge_shrink+0x334/0x3f0 super_cache_scan+0x176/0x180 shrink_slab+0x275/0x460 shrink_node+0x10e/0x320 node_reclaim+0x19d/0x250 get_page_from_freelist+0x16a/0xac0 ? radix_tree_lookup_slot+0x1e/0x50 ? find_lock_entry+0x45/0x80 ? shmem_getpage_gfp.isra.34+0xe5/0xc80 __alloc_pages_nodemask+0x111/0x2c0 pte_alloc_one+0x13/0x40 __pte_alloc+0x19/0x100 alloc_set_pte+0x468/0x4c0 finish_fault+0x3a/0x70 __handle_mm_fault+0x94a/0x1190 handle_mm_fault+0xf2/0x210 __do_page_fault+0x253/0x4d0 do_page_fault+0x33/0x120 ? page_fault+0x36/0x60 page_fault+0x4c/0x60 ---------- And since switches= and seq= did not change, crm_node kept sleeping. libvirtd remained stuck waiting for crm_node. But something already went wrong more than one day ago. ---------- libvirtd D 0 1125 1 0x00000080 Call Trace: ? __schedule+0x1dc/0x770 schedule+0x32/0x80 rwsem_down_write_failed+0x20d/0x380 ? ida_get_new_above+0x110/0x3b0 call_rwsem_down_write_failed+0x13/0x20 down_write+0x29/0x40 register_shrinker+0x45/0xa0 sget_userns+0x468/0x4a0 ? get_anon_bdev+0x100/0x100 ? shmem_create+0x20/0x20 mount_nodev+0x2a/0xa0 mount_fs+0x34/0x150 vfs_kern_mount+0x62/0x120 do_mount+0x1ee/0xc50 SyS_mount+0x7e/0xd0 do_syscall_64+0x61/0x1a0 entry_SYSCALL64_slow_path+0x25/0x25 ---------- > I'm not sure if this is relevant, but the load average is wrong on the > 4.14.15 machine: > load average: 1308.46, 1246.69, 1078.29 > There is no way those numbers are correct, top shows nothing spinning > and vmstat only shows 1-4 processes in a running or blocked state. If I recall correctly, insanely growing load average is a possible sign of processes getting stuck one by one as one is created (by e.g. crond). > > Here are the pid stacks in D states from ps above: > > ~]# cat /proc/27163/stack > [<ffffffff900cd0d2>] io_schedule+0x12/0x40 > [<ffffffff901b4735>] __lock_page+0x105/0x150 > [<ffffffff901b4e61>] pagecache_get_page+0x161/0x210 > [<ffffffff901d4c74>] shmem_unused_huge_shrink+0x334/0x3f0 > [<ffffffff90251746>] super_cache_scan+0x176/0x180 > [<ffffffff901cb885>] shrink_slab+0x275/0x460 > [<ffffffff901d0d4e>] shrink_node+0x10e/0x320 > [<ffffffff901d10fd>] node_reclaim+0x19d/0x250 > [<ffffffff901be1ca>] get_page_from_freelist+0x16a/0xac0 > [<ffffffff901bef81>] __alloc_pages_nodemask+0x111/0x2c0 > [<ffffffff9006dbc3>] pte_alloc_one+0x13/0x40 > [<ffffffff901ef4e9>] __pte_alloc+0x19/0x100 > [<ffffffff901f1978>] alloc_set_pte+0x468/0x4c0 > [<ffffffff901f1a0a>] finish_fault+0x3a/0x70 > [<ffffffff901f385a>] __handle_mm_fault+0x94a/0x1190 > [<ffffffff901f4192>] handle_mm_fault+0xf2/0x210 > [<ffffffff900682a3>] __do_page_fault+0x253/0x4d0 > [<ffffffff90068553>] do_page_fault+0x33/0x120 > [<ffffffff908019dc>] page_fault+0x4c/0x60 > [<ffffffffffffffff>] 0xffffffffffffffff > > > ~]# cat /proc/1125/stack > [<ffffffff907538d3>] call_rwsem_down_write_failed+0x13/0x20 > [<ffffffff901cbb45>] register_shrinker+0x45/0xa0 > [<ffffffff90251168>] sget_userns+0x468/0x4a0 > [<ffffffff9025126a>] mount_nodev+0x2a/0xa0 > [<ffffffff90251de4>] mount_fs+0x34/0x150 > [<ffffffff902703f2>] vfs_kern_mount+0x62/0x120 > [<ffffffff90272c0e>] do_mount+0x1ee/0xc50 > [<ffffffff9027397e>] SyS_mount+0x7e/0xd0 > [<ffffffff90003831>] do_syscall_64+0x61/0x1a0 > [<ffffffff9080012c>] entry_SYSCALL64_slow_path+0x25/0x25 > [<ffffffffffffffff>] 0xffffffffffffffff > > > > If you have any ideas on creating an easy way to reproduce the problem, > > > then I can bisect---but bisecting one day at a time will take a long time, > > > and could be prone to bugs which I would like to avoid on this production > > > system. > > > > > Thinking from SysRq-t output, I feel that some disk read is stuck. > > Possibly. I would not expect a hardware problem since we see this on two > different systems with different kernel versions. > > > Since rsyslogd failed to catch portion of SysRq-t output, I can't confirm > > whether register_shrinker() was in progress (nor all kernel worker threads > > were reported). > > As linked above, I was able to get the full trace with netconsole. > > > But what I was surprised is number of kernel worker threads. > > "grep ^kworker/ | sort" matched 314 threads and "grep ^kworker/0:" > > matched 244. > > We have many DRBD volumes and LVM volumes, most of which are dm-thin, so > that might be why. Also these servers have both scsi-mq and dm-mq enabled. Ideally you could reproduce without DRBD, LVM, bcache etc. , for Marc MERLIN's report ( http://lkml.kernel.org/r/20170502041235.zqmywvj5tiiom3jk@xxxxxxxxxxx ) was using (at least) bcache. It might be a bug which fails to submit I/O request. > > > > One of workqueue threads was waiting at > > > > ---------- > > static void *new_read(struct dm_bufio_client *c, sector_t block, > > enum new_flag nf, struct dm_buffer **bp) > > { > > int need_submit; > > struct dm_buffer *b; > > > > LIST_HEAD(write_list); > > > > dm_bufio_lock(c); > > b = __bufio_new(c, block, nf, &need_submit, &write_list); > > #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING > > if (b && b->hold_count == 1) > > buffer_record_stack(b); > > #endif > > dm_bufio_unlock(c); > > > > __flush_write_list(&write_list); > > > > if (!b) > > return NULL; > > > > if (need_submit) > > submit_io(b, READ, read_endio); > > > > wait_on_bit_io(&b->state, B_READING, TASK_UNINTERRUPTIBLE); // <= here > > > > if (b->read_error) { > > int error = blk_status_to_errno(b->read_error); > > > > dm_bufio_release(b); > > > > return ERR_PTR(error); > > } > > > > *bp = b; > > > > return b->data; > > } > > ---------- > > > > but what are possible reasons? Does this request depend on workqueue availability? > > We are using dm-thin which uses dm-bufio. The dm-thin pools are working > properly, so I don't think this is the problem---or at least if it is > the problem, it isn't affecting the thin pool. Some suggestions: You can enlarge kernel printk() buffer size using log_buf_len= kernel command line parameter. As your system is large, you could allocate e.g. log_buf_len=67108864 . Then, you can read kernel buffer using dmesg command (e.g. /usr/bin/dmesg ). You can add timestamp to printk() messages by doing below command. ---------- # echo Y > /sys/module/printk/parameters/time ---------- Since crm_node starts stalling rather early, you can watch out for kernel messages and userspace messages which were printed around crm_node started stalling, for there might be some events (e.g. error recovery) occurring. I'm not sure but maybe page_owner gives us some clue. (Michal, what do you think?) You can compile your kernel with CONFIG_PAGE_OWNER=y and boot your kernel with page_owner=on kernel command line option added. But that alone does not tell on which "struct page *" processes got stuck. We will need to call dump_page() for reporting specific "struct page *". One of approaches would be to run a SystemTap script shown below (in background using -F option) and check how stalling pages has been allocated. There might be some characteristics with stalling pages. ---------- # stap -DSTP_NO_OVERLOAD=1 -F -g - << "EOF" global waiting_pages; probe kernel.function("__lock_page").call { waiting_pages[$__page] = gettimeofday_s(); } probe kernel.function("__lock_page").return { delete waiting_pages[@entry($__page)]; } function my_dump_page(page:long) %{ dump_page((struct page *) STAP_ARG_page, "lock_page() stalling"); %} probe timer.s(60) { now = gettimeofday_s(); foreach (page in waiting_pages) if (now - waiting_pages[page] >= 30) my_dump_page(page); } EOF ---------- An example allocated by plain write() (though this is without stall period because I can't reproduce your problem) is shown below. ---------- [ 164.573566] page:fffff3a9024b17c0 count:4 mapcount:0 mapping:ffff8811e2876d68 index:0x5827 [ 164.584758] flags: 0x1fffff800010a9(locked|waiters|uptodate|lru|private) [ 164.593678] raw: 001fffff800010a9 ffff8811e2876d68 0000000000005827 00000004ffffffff [ 164.603410] raw: fffff3a9024b17a0 fffff3a9024cc420 ffff8811e2be27b8 ffff881269fdf800 [ 164.608676] page dumped because: lock_page() stalling [ 164.612558] page->mem_cgroup:ffff881269fdf800 [ 164.615770] page allocated via order 0, migratetype Movable, gfp_mask 0x1c2004a(GFP_NOFS|__GFP_HIGHMEM|__GFP_HARDWALL|__GFP_MOVABLE|__GFP_WRITE) [ 164.623143] __alloc_pages_nodemask+0x184/0x470 [ 164.626939] pagecache_get_page+0xbe/0x310 [ 164.630028] grab_cache_page_write_begin+0x1f/0x40 [ 164.633436] iomap_write_begin.constprop.15+0x5a/0x150 [ 164.636013] iomap_write_actor+0x95/0x180 [ 164.637955] iomap_apply+0xa4/0x110 [ 164.639710] iomap_file_buffered_write+0x61/0x80 [ 164.641796] xfs_file_buffered_aio_write+0xfe/0x3b0 [xfs] [ 164.643945] xfs_file_write_iter+0xfc/0x150 [xfs] [ 164.646290] __vfs_write+0xfc/0x170 [ 164.648048] vfs_write+0xc5/0x1b0 [ 164.649760] SyS_write+0x55/0xc0 [ 164.651317] do_syscall_64+0x66/0x210 [ 164.652994] return_from_SYSCALL_64+0x0/0x75 ---------- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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