Re: [PATCH v3] lockdep: Teach lockdep about memalloc_noio_save

Mike Galbraith
2017-03-03T06:52:21Z

On Wed, 2017-03-01 at 16:46 +0100, Peter Zijlstra wrote:
> On Wed, Mar 01, 2017 at 01:29:57PM +0200, Nikolay Borisov wrote:
> > Commit 21caf2fc1931 ("mm: teach mm by current context info to not do I/O
> > during memory allocation") added the memalloc_noio_(save|restore) functions
> > to enable people to modify the MM behavior by disbaling I/O during memory
> > allocation. This was further extended in Fixes: 934f3072c17c ("mm: clear
> > __GFP_FS when PF_MEMALLOC_NOIO is set"). memalloc_noio_* functions prevent
> > allocation paths recursing back into the filesystem without explicitly
> > changing the flags for every allocation site. However, lockdep hasn't been
> > keeping up with the changes and it entirely misses handling the memalloc_noio
> > adjustments. Instead, it is left to the callers of __lockdep_trace_alloc to
> > call the functino after they have shaven the respective GFP flags.
> >
> > Let's fix this by making lockdep explicitly do the shaving of respective
> > GFP flags.
>
> I edited that to look like the below, then my compiler said:
>
> ../kernel/locking/lockdep.c: In function ‘lockdep_set_current_reclaim_state’:
> ../kernel/locking/lockdep.c:3866:33: error: implicit declaration of function ‘memalloc_noio_flags’ [-Werror=implicit-function-declaration]
> current->lockdep_reclaim_gfp = memalloc_noio_flags(gfp_mask);

(ah, another shiny lockdep thingy... /me adds include, tries it)

I had hoped (silly me) that this would make annoying btrfs gripe
finally go the hell away, but alas, didn't happen.

[ 4968.346159] =========================================================
[ 4968.346160] [ INFO: possible irq lock inversion dependency detected ]
[ 4968.346163] 4.11.0-rt9-rt #179 Tainted: G W E
[ 4968.346164] ---------------------------------------------------------
[ 4968.346165] kswapd3/1337 just changed the state of lock:
[ 4968.346167] (&delayed_node->mutex){+.+.-.}, at: [<ffffffffa0389fbf>] __btrfs_release_delayed_node+0x3f/0x2f0 [btrfs]
[ 4968.346215] but this lock took another, RECLAIM_FS-unsafe lock in the past:
[ 4968.346215] (pcpu_alloc_mutex){+.+.+.}
[ 4968.346216]

and interrupts could create inverse lock ordering between them.

[ 4968.346217]
other info that might help us debug this:
[ 4968.346217] Chain exists of:
&delayed_node->mutex --> &fs_info->commit_root_sem --> pcpu_alloc_mutex

[ 4968.346218] Possible interrupt unsafe locking scenario:

[ 4968.346219] CPU0 CPU1
[ 4968.346219] ---- ----
[ 4968.346219] lock(pcpu_alloc_mutex);
[ 4968.346220] local_irq_disable();
[ 4968.346220] lock(&delayed_node->mutex);
[ 4968.346221] lock(&fs_info->commit_root_sem);
[ 4968.346221] <Interrupt>
[ 4968.346221] lock(&delayed_node->mutex);
[ 4968.346222]
*** DEADLOCK ***

[ 4968.346223] 2 locks held by kswapd3/1337:
[ 4968.346223] #0: (shrinker_rwsem){+.+...}, at: [<ffffffff811f447a>] shrink_slab+0x7a/0x6c0
[ 4968.346231] #1: (&type->s_umount_key#26){++++..}, at: [<ffffffff8127815b>] trylock_super+0x1b/0x50
[ 4968.346236]
the shortest dependencies between 2nd lock and 1st lock:
[ 4968.346238] -> (pcpu_alloc_mutex){+.+.+.} ops: 4124 {
[ 4968.346239] HARDIRQ-ON-W at:
[ 4968.346246] __lock_acquire+0x8ec/0x14f0
[ 4968.346247] lock_acquire+0xbd/0x250
[ 4968.346252] _mutex_lock+0x31/0x40
[ 4968.346258] pcpu_alloc+0x197/0x5a0
[ 4968.346260] __alloc_percpu+0x15/0x20
[ 4968.346264] setup_zone_pageset+0x1f/0x71
[ 4968.346273] setup_per_cpu_pageset+0x23/0x65
[ 4968.346279] start_kernel+0x3d4/0x496
[ 4968.346281] x86_64_start_reservations+0x2a/0x2c
[ 4968.346282] x86_64_start_kernel+0x13d/0x14c
[ 4968.346285] verify_cpu+0x0/0xfc
[ 4968.346286] SOFTIRQ-ON-W at:
[ 4968.346287] __lock_acquire+0x285/0x14f0
[ 4968.346288] lock_acquire+0xbd/0x250
[ 4968.346289] _mutex_lock+0x31/0x40
[ 4968.346291] pcpu_alloc+0x197/0x5a0
[ 4968.346292] __alloc_percpu+0x15/0x20
[ 4968.346293] setup_zone_pageset+0x1f/0x71
[ 4968.346295] setup_per_cpu_pageset+0x23/0x65
[ 4968.346296] start_kernel+0x3d4/0x496
[ 4968.346298] x86_64_start_reservations+0x2a/0x2c
[ 4968.346299] x86_64_start_kernel+0x13d/0x14c
[ 4968.346300] verify_cpu+0x0/0xfc
[ 4968.346301] RECLAIM_FS-ON-W at:
[ 4968.346303] mark_held_locks+0x66/0x90
[ 4968.346304] lockdep_trace_alloc+0x7d/0xf0
[ 4968.346309] __kmalloc+0x4f/0x340
[ 4968.346310] pcpu_mem_zalloc+0x37/0x70
[ 4968.346312] pcpu_extend_area_map+0x2f/0xd0
[ 4968.346313] pcpu_alloc+0x3af/0x5a0
[ 4968.346315] __alloc_percpu+0x15/0x20
[ 4968.346324] smpcfd_prepare_cpu+0x4a/0x60
[ 4968.346327] cpuhp_invoke_callback+0x248/0x9d0
[ 4968.346328] cpuhp_up_callbacks+0x37/0xb0
[ 4968.346329] _cpu_up+0x7c/0xc0
[ 4968.346330] do_cpu_up+0x87/0xb0
[ 4968.346331] cpu_up+0x13/0x20
[ 4968.346332] smp_init+0x79/0xe1
[ 4968.346334] kernel_init_freeable+0x1a7/0x2c7
[ 4968.346335] kernel_init+0xe/0x100
[ 4968.346337] ret_from_fork+0x31/0x40
[ 4968.346338] INITIAL USE at:
[ 4968.346339] __lock_acquire+0x2d0/0x14f0
[ 4968.346340] lock_acquire+0xbd/0x250
[ 4968.346341] _mutex_lock+0x31/0x40
[ 4968.346343] pcpu_alloc+0x197/0x5a0
[ 4968.346344] __alloc_percpu+0x15/0x20
[ 4968.346346] kmem_cache_open+0x316/0x3d0
[ 4968.346347] __kmem_cache_create+0x2d/0x160
[ 4968.346349] create_boot_cache+0x8b/0xb3
[ 4968.346352] kmem_cache_init+0xa4/0x171
[ 4968.346354] start_kernel+0x242/0x496
[ 4968.346355] x86_64_start_reservations+0x2a/0x2c
[ 4968.346357] x86_64_start_kernel+0x13d/0x14c
[ 4968.346357] verify_cpu+0x0/0xfc
[ 4968.346358] }
[ 4968.346363] ... key at: [<ffffffff81c9a798>] pcpu_alloc_mutex+0x58/0x80
[ 4968.346363] ... acquired at:
[ 4968.346364] lock_acquire+0xbd/0x250
[ 4968.346365] _mutex_lock+0x31/0x40
[ 4968.346366] pcpu_alloc+0x197/0x5a0
[ 4968.346368] __alloc_percpu_gfp+0x12/0x20
[ 4968.346371] __percpu_counter_init+0x55/0xd0
[ 4968.346384] btrfs_init_fs_root+0x9e/0x1e0 [btrfs]
[ 4968.346396] btrfs_get_fs_root.part.51+0x5f/0x150 [btrfs]
[ 4968.346406] btrfs_get_fs_root+0x44/0xa0 [btrfs]
[ 4968.346420] __resolve_indirect_refs+0x155/0x880 [btrfs]
[ 4968.346433] find_parent_nodes+0x541/0x8d0 [btrfs]
[ 4968.346445] __btrfs_find_all_roots+0xc6/0x130 [btrfs]
[ 4968.346457] btrfs_find_all_roots+0x55/0x70 [btrfs]
[ 4968.346469] btrfs_qgroup_trace_extent_post+0x25/0x40 [btrfs]
[ 4968.346480] btrfs_add_delayed_tree_ref+0x1c6/0x1f0 [btrfs]
[ 4968.346491] btrfs_free_tree_block+0x8a/0x390 [btrfs]
[ 4968.346499] __btrfs_cow_block+0x2dc/0x610 [btrfs]
[ 4968.346508] btrfs_cow_block+0x11e/0x300 [btrfs]
[ 4968.346516] btrfs_search_slot+0x1e2/0x970 [btrfs]
[ 4968.346527] btrfs_lookup_inode+0x2f/0xa0 [btrfs]
[ 4968.346539] __btrfs_update_delayed_inode+0x65/0x210 [btrfs]
[ 4968.346550] btrfs_async_run_delayed_root+0x1f6/0x220 [btrfs]
[ 4968.346562] normal_work_helper+0x1bd/0x620 [btrfs]
[ 4968.346574] btrfs_delayed_meta_helper+0x12/0x20 [btrfs]
[ 4968.346577] process_one_work+0x1f0/0x700
[ 4968.346578] worker_thread+0x171/0x530
[ 4968.346579] kthread+0x10c/0x140
[ 4968.346580] ret_from_fork+0x31/0x40

[ 4968.346581] -> (&fs_info->commit_root_sem){++++..} ops: 527801 {
[ 4968.346583] HARDIRQ-ON-W at:
[ 4968.346584] __lock_acquire+0x8ec/0x14f0
[ 4968.346585] lock_acquire+0xbd/0x250
[ 4968.346588] rt_down_write+0x31/0x40
[ 4968.346597] cache_block_group+0x2ad/0x400 [btrfs]
[ 4968.346607] find_free_extent+0x12a5/0x1510 [btrfs]
[ 4968.346616] btrfs_reserve_extent+0xdb/0x190 [btrfs]
[ 4968.346625] btrfs_alloc_tree_block+0x1a1/0x4b0 [btrfs]
[ 4968.346634] __btrfs_cow_block+0x12f/0x610 [btrfs]
[ 4968.346643] btrfs_cow_block+0x11e/0x300 [btrfs]
[ 4968.346651] btrfs_search_slot+0x1e2/0x970 [btrfs]
[ 4968.346664] btrfs_update_device+0x68/0x190 [btrfs]
[ 4968.346676] btrfs_remove_chunk+0x348/0xa30 [btrfs]
[ 4968.346686] btrfs_delete_unused_bgs+0x2f8/0x450 [btrfs]
[ 4968.346696] cleaner_kthread+0x16e/0x1a0 [btrfs]
[ 4968.346698] kthread+0x10c/0x140
[ 4968.346699] ret_from_fork+0x31/0x40
[ 4968.346699] HARDIRQ-ON-R at:
[ 4968.346701] __lock_acquire+0x262/0x14f0
[ 4968.346702] lock_acquire+0xbd/0x250
[ 4968.346703] __rt_down_read+0x32/0x50
[ 4968.346704] rt_down_read+0x10/0x20
[ 4968.346713] caching_thread+0x64/0x4e0 [btrfs]
[ 4968.346726] normal_work_helper+0x1bd/0x620 [btrfs]
[ 4968.346737] btrfs_cache_helper+0x12/0x20 [btrfs]
[ 4968.346738] process_one_work+0x1f0/0x700
[ 4968.346739] worker_thread+0x171/0x530
[ 4968.346741] kthread+0x10c/0x140
[ 4968.346742] ret_from_fork+0x31/0x40
[ 4968.346742] SOFTIRQ-ON-W at:
[ 4968.346743] __lock_acquire+0x285/0x14f0
[ 4968.346744] lock_acquire+0xbd/0x250
[ 4968.346746] rt_down_write+0x31/0x40
[ 4968.346755] cache_block_group+0x2ad/0x400 [btrfs]
[ 4968.346764] find_free_extent+0x12a5/0x1510 [btrfs]
[ 4968.346773] btrfs_reserve_extent+0xdb/0x190 [btrfs]
[ 4968.346782] btrfs_alloc_tree_block+0x1a1/0x4b0 [btrfs]
[ 4968.346791] __btrfs_cow_block+0x12f/0x610 [btrfs]
[ 4968.346799] btrfs_cow_block+0x11e/0x300 [btrfs]
[ 4968.346808] btrfs_search_slot+0x1e2/0x970 [btrfs]
[ 4968.346820] btrfs_update_device+0x68/0x190 [btrfs]
[ 4968.346832] btrfs_remove_chunk+0x348/0xa30 [btrfs]
[ 4968.346841] btrfs_delete_unused_bgs+0x2f8/0x450 [btrfs]
[ 4968.346851] cleaner_kthread+0x16e/0x1a0 [btrfs]
[ 4968.346853] kthread+0x10c/0x140
[ 4968.346854] ret_from_fork+0x31/0x40
[ 4968.346854] SOFTIRQ-ON-R at:
[ 4968.346856] __lock_acquire+0x285/0x14f0
[ 4968.346857] lock_acquire+0xbd/0x250
[ 4968.346858] __rt_down_read+0x32/0x50
[ 4968.346859] rt_down_read+0x10/0x20
[ 4968.346868] caching_thread+0x64/0x4e0 [btrfs]
[ 4968.346880] normal_work_helper+0x1bd/0x620 [btrfs]
[ 4968.346892] btrfs_cache_helper+0x12/0x20 [btrfs]
[ 4968.346893] process_one_work+0x1f0/0x700
[ 4968.346894] worker_thread+0x171/0x530
[ 4968.346895] kthread+0x10c/0x140
[ 4968.346896] ret_from_fork+0x31/0x40
[ 4968.346896] INITIAL USE at:
[ 4968.346898] __lock_acquire+0x2d0/0x14f0
[ 4968.346899] lock_acquire+0xbd/0x250
[ 4968.346900] rt_down_write+0x31/0x40
[ 4968.346909] cache_block_group+0x2ad/0x400 [btrfs]
[ 4968.346918] find_free_extent+0x12a5/0x1510 [btrfs]
[ 4968.346927] btrfs_reserve_extent+0xdb/0x190 [btrfs]
[ 4968.346935] btrfs_alloc_tree_block+0x1a1/0x4b0 [btrfs]
[ 4968.346944] __btrfs_cow_block+0x12f/0x610 [btrfs]
[ 4968.346952] btrfs_cow_block+0x11e/0x300 [btrfs]
[ 4968.346961] btrfs_search_slot+0x1e2/0x970 [btrfs]
[ 4968.346973] btrfs_update_device+0x68/0x190 [btrfs]
[ 4968.346984] btrfs_remove_chunk+0x348/0xa30 [btrfs]
[ 4968.346993] btrfs_delete_unused_bgs+0x2f8/0x450 [btrfs]
[ 4968.347003] cleaner_kthread+0x16e/0x1a0 [btrfs]
[ 4968.347005] kthread+0x10c/0x140
[ 4968.347006] ret_from_fork+0x31/0x40
[ 4968.347006] }
[ 4968.347022] ... key at: [<ffffffffa03dd058>] __key.59194+0x0/0xfffffffffffd7fa8 [btrfs]
[ 4968.347022] ... acquired at:
[ 4968.347023] lock_acquire+0xbd/0x250
[ 4968.347025] __rt_down_read+0x32/0x50
[ 4968.347026] rt_down_read+0x10/0x20
[ 4968.347039] btrfs_find_all_roots+0x3e/0x70 [btrfs]
[ 4968.347051] btrfs_qgroup_trace_extent_post+0x25/0x40 [btrfs]
[ 4968.347063] btrfs_add_delayed_tree_ref+0x1c6/0x1f0 [btrfs]
[ 4968.347072] btrfs_alloc_tree_block+0x38c/0x4b0 [btrfs]
[ 4968.347080] __btrfs_cow_block+0x12f/0x610 [btrfs]
[ 4968.347089] btrfs_cow_block+0x11e/0x300 [btrfs]
[ 4968.347097] btrfs_search_slot+0x1e2/0x970 [btrfs]
[ 4968.347107] btrfs_lookup_inode+0x2f/0xa0 [btrfs]
[ 4968.347119] __btrfs_update_delayed_inode+0x65/0x210 [btrfs]
[ 4968.347130] btrfs_commit_inode_delayed_inode+0x123/0x130 [btrfs]
[ 4968.347142] btrfs_evict_inode+0x4a3/0x750 [btrfs]
[ 4968.347144] evict+0xd1/0x1a0
[ 4968.347145] iput+0x1fe/0x320
[ 4968.347147] do_unlinkat+0x17b/0x2a0
[ 4968.347148] SyS_unlink+0x16/0x20
[ 4968.347149] entry_SYSCALL_64_fastpath+0x1f/0xc2

[ 4968.347149] -> (&delayed_node->mutex){+.+.-.} ops: 12427409 {
[ 4968.347151] HARDIRQ-ON-W at:
[ 4968.347152] __lock_acquire+0x8ec/0x14f0
[ 4968.347153] lock_acquire+0xbd/0x250
[ 4968.347154] _mutex_lock+0x31/0x40
[ 4968.347166] btrfs_delayed_update_inode+0x4a/0x820 [btrfs]
[ 4968.347177] btrfs_update_inode+0x8c/0x110 [btrfs]
[ 4968.347187] btrfs_dirty_inode+0x69/0xe0 [btrfs]
[ 4968.347197] btrfs_update_time+0x64/0xc0 [btrfs]
[ 4968.347198] touch_atime+0x89/0xb0
[ 4968.347200] generic_file_read_iter+0x750/0x8d0
[ 4968.347204] __vfs_read+0xc1/0x130
[ 4968.347205] vfs_read+0xa1/0x180
[ 4968.347207] SyS_read+0x49/0xa0
[ 4968.347208] entry_SYSCALL_64_fastpath+0x1f/0xc2
[ 4968.347208] SOFTIRQ-ON-W at:
[ 4968.347210] __lock_acquire+0x285/0x14f0
[ 4968.347211] lock_acquire+0xbd/0x250
[ 4968.347211] _mutex_lock+0x31/0x40
[ 4968.347223] btrfs_delayed_update_inode+0x4a/0x820 [btrfs]
[ 4968.347232] btrfs_update_inode+0x8c/0x110 [btrfs]
[ 4968.347241] btrfs_dirty_inode+0x69/0xe0 [btrfs]
[ 4968.347250] btrfs_update_time+0x64/0xc0 [btrfs]
[ 4968.347251] touch_atime+0x89/0xb0
[ 4968.347252] generic_file_read_iter+0x750/0x8d0
[ 4968.347254] __vfs_read+0xc1/0x130
[ 4968.347255] vfs_read+0xa1/0x180
[ 4968.347257] SyS_read+0x49/0xa0
[ 4968.347258] entry_SYSCALL_64_fastpath+0x1f/0xc2
[ 4968.347258] IN-RECLAIM_FS-W at:
[ 4968.347259] __lock_acquire+0x2b8/0x14f0
[ 4968.347260] lock_acquire+0xbd/0x250
[ 4968.347261] _mutex_lock+0x31/0x40
[ 4968.347273] __btrfs_release_delayed_node+0x3f/0x2f0 [btrfs]
[ 4968.347284] btrfs_remove_delayed_node+0x2a/0x30 [btrfs]
[ 4968.347294] btrfs_evict_inode+0x390/0x750 [btrfs]
[ 4968.347295] evict+0xd1/0x1a0
[ 4968.347296] dispose_list+0x4d/0x70
[ 4968.347296] prune_icache_sb+0x4b/0x60
[ 4968.347297] super_cache_scan+0x141/0x190
[ 4968.347299] shrink_slab+0x277/0x6c0
[ 4968.347301] shrink_node+0x2e3/0x2f0
[ 4968.347302] kswapd+0x34f/0x980
[ 4968.347304] kthread+0x10c/0x140
[ 4968.347305] ret_from_fork+0x31/0x40
[ 4968.347305] INITIAL USE at:
[ 4968.347306] __lock_acquire+0x2d0/0x14f0
[ 4968.347307] lock_acquire+0xbd/0x250
[ 4968.347308] _mutex_lock+0x31/0x40
[ 4968.347319] btrfs_delayed_update_inode+0x4a/0x820 [btrfs]
[ 4968.347329] btrfs_update_inode+0x8c/0x110 [btrfs]
[ 4968.347337] btrfs_dirty_inode+0x69/0xe0 [btrfs]
[ 4968.347346] btrfs_update_time+0x64/0xc0 [btrfs]
[ 4968.347347] touch_atime+0x89/0xb0
[ 4968.347348] generic_file_read_iter+0x750/0x8d0
[ 4968.347350] __vfs_read+0xc1/0x130
[ 4968.347351] vfs_read+0xa1/0x180
[ 4968.347353] SyS_read+0x49/0xa0
[ 4968.347354] entry_SYSCALL_64_fastpath+0x1f/0xc2
[ 4968.347354] }
[ 4968.347369] ... key at: [<ffffffffa03e1260>] __key.55236+0x0/0xfffffffffffd3da0 [btrfs]
[ 4968.347370] ... acquired at:
[ 4968.347371] check_usage_forwards+0x131/0x140
[ 4968.347372] mark_lock+0x191/0x290
[ 4968.347373] __lock_acquire+0x2b8/0x14f0
[ 4968.347374] lock_acquire+0xbd/0x250
[ 4968.347374] _mutex_lock+0x31/0x40
[ 4968.347386] __btrfs_release_delayed_node+0x3f/0x2f0 [btrfs]
[ 4968.347397] btrfs_remove_delayed_node+0x2a/0x30 [btrfs]
[ 4968.347407] btrfs_evict_inode+0x390/0x750 [btrfs]
[ 4968.347407] evict+0xd1/0x1a0
[ 4968.347408] dispose_list+0x4d/0x70
[ 4968.347409] prune_icache_sb+0x4b/0x60
[ 4968.347410] super_cache_scan+0x141/0x190
[ 4968.347411] shrink_slab+0x277/0x6c0
[ 4968.347413] shrink_node+0x2e3/0x2f0
[ 4968.347414] kswapd+0x34f/0x980
[ 4968.347416] kthread+0x10c/0x140
[ 4968.347417] ret_from_fork+0x31/0x40

[ 4968.347417]
stack backtrace:
[ 4968.347419] CPU: 54 PID: 1337 Comm: kswapd3 Tainted: G W E 4.11.0-rt9-rt #179
[ 4968.347421] Hardware name: Intel Corporation BRICKLAND/BRICKLAND, BIOS BRHSXSD1.86B.0056.R01.1409242327 09/24/2014
[ 4968.347421] Call Trace:
[ 4968.347426] dump_stack+0x85/0xc8
[ 4968.347428] print_irq_inversion_bug.part.37+0x1ac/0x1b8
[ 4968.347430] check_usage_forwards+0x131/0x140
[ 4968.347432] ? check_usage_backwards+0x130/0x130
[ 4968.347434] mark_lock+0x191/0x290
[ 4968.347435] __lock_acquire+0x2b8/0x14f0
[ 4968.347436] ? check_irq_usage+0x83/0xb0
[ 4968.347438] ? __lock_acquire+0xb1b/0x14f0
[ 4968.347440] lock_acquire+0xbd/0x250
[ 4968.347451] ? __btrfs_release_delayed_node+0x3f/0x2f0 [btrfs]
[ 4968.347453] _mutex_lock+0x31/0x40
[ 4968.347463] ? __btrfs_release_delayed_node+0x3f/0x2f0 [btrfs]
[ 4968.347474] __btrfs_release_delayed_node+0x3f/0x2f0 [btrfs]
[ 4968.347475] ? unpin_current_cpu+0x16/0x70
[ 4968.347486] btrfs_remove_delayed_node+0x2a/0x30 [btrfs]
[ 4968.347496] btrfs_evict_inode+0x390/0x750 [btrfs]
[ 4968.347501] ? debug_smp_processor_id+0x17/0x20
[ 4968.347503] ? rt_spin_unlock+0x3d/0x50
[ 4968.347504] evict+0xd1/0x1a0
[ 4968.347505] dispose_list+0x4d/0x70
[ 4968.347506] prune_icache_sb+0x4b/0x60
[ 4968.347508] super_cache_scan+0x141/0x190
[ 4968.347510] shrink_slab+0x277/0x6c0
[ 4968.347514] shrink_node+0x2e3/0x2f0
[ 4968.347516] kswapd+0x34f/0x980
[ 4968.347519] kthread+0x10c/0x140
[ 4968.347521] ? mem_cgroup_shrink_node+0x390/0x390
[ 4968.347523] ? kthread_park+0x90/0x90
[ 4968.347524] ret_from_fork+0x31/0x40