On Thu, 3 Feb 2022, Mel Gorman wrote: > A soft lockup bug in kcompactd was reported in a private bugzilla with > the following visible in dmesg; > > [15980.045209][ C33] watchdog: BUG: soft lockup - CPU#33 stuck for 26s! [kcompactd0:479] > [16008.044989][ C33] watchdog: BUG: soft lockup - CPU#33 stuck for 52s! [kcompactd0:479] > [16036.044768][ C33] watchdog: BUG: soft lockup - CPU#33 stuck for 78s! [kcompactd0:479] > [16064.044548][ C33] watchdog: BUG: soft lockup - CPU#33 stuck for 104s! [kcompactd0:479] > > The machine had 256G of RAM with no swap and an earlier failed allocation > indicated that node 0 where kcompactd was run was potentially > unreclaimable; > > Node 0 active_anon:29355112kB inactive_anon:2913528kB active_file:0kB > inactive_file:0kB unevictable:64kB isolated(anon):0kB isolated(file):0kB > mapped:8kB dirty:0kB writeback:0kB shmem:26780kB shmem_thp: > 0kB shmem_pmdmapped: 0kB anon_thp: 23480320kB writeback_tmp:0kB > kernel_stack:2272kB pagetables:24500kB all_unreclaimable? yes > > Vlastimil Babka investigated a crash dump and found that a task migrating pages > was trying to drain PCP lists; > > PID: 52922 TASK: ffff969f820e5000 CPU: 19 COMMAND: "kworker/u128:3" > #0 [ffffaf4e4f4c3848] __schedule at ffffffffb840116d > #1 [ffffaf4e4f4c3908] schedule at ffffffffb8401e81 > #2 [ffffaf4e4f4c3918] schedule_timeout at ffffffffb84066e8 > #3 [ffffaf4e4f4c3990] wait_for_completion at ffffffffb8403072 > #4 [ffffaf4e4f4c39d0] __flush_work at ffffffffb7ac3e4d > #5 [ffffaf4e4f4c3a48] __drain_all_pages at ffffffffb7cb707c > #6 [ffffaf4e4f4c3a80] __alloc_pages_slowpath.constprop.114 at ffffffffb7cbd9dd > #7 [ffffaf4e4f4c3b60] __alloc_pages at ffffffffb7cbe4f5 > #8 [ffffaf4e4f4c3bc0] alloc_migration_target at ffffffffb7cf329c > #9 [ffffaf4e4f4c3bf0] migrate_pages at ffffffffb7cf6d15 > 10 [ffffaf4e4f4c3cb0] migrate_to_node at ffffffffb7cdb5aa > 11 [ffffaf4e4f4c3da8] do_migrate_pages at ffffffffb7cdcf26 > 12 [ffffaf4e4f4c3e88] cpuset_migrate_mm_workfn at ffffffffb7b859d2 > 13 [ffffaf4e4f4c3e98] process_one_work at ffffffffb7ac45f3 > 14 [ffffaf4e4f4c3ed8] worker_thread at ffffffffb7ac47fd > 15 [ffffaf4e4f4c3f10] kthread at ffffffffb7acbdc6 > 16 [ffffaf4e4f4c3f50] ret_from_fork at ffffffffb7a047e2 > > The root of the problem is that kcompact0 is not rescheduling on a CPU > while a task that has isolated a large number of the pages from the > LRU is waiting on kcompact0 to reschedule so the pages can be released. > While shrink_inactive_list() only loops once around too_many_isolated, > reclaim can continue without rescheduling if sc->skipped_deactivate == > 1 which could happen if there was no file LRU and the inactive anon list > was not low. > > Debugged-by: Vlastimil Babka <vbabka@xxxxxxx> > Signed-off-by: Mel Gorman <mgorman@xxxxxxx> Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
