From: Mel Gorman mgorman@suse.de
commit b485c6f1f9f54b81443efda5f3d8a5036ba2cd91 upstream.
A soft lockup bug in kcompactd was reported in a private bugzilla with the following visible in dmesg;
watchdog: BUG: soft lockup - CPU#33 stuck for 26s! [kcompactd0:479] watchdog: BUG: soft lockup - CPU#33 stuck for 52s! [kcompactd0:479] watchdog: BUG: soft lockup - CPU#33 stuck for 78s! [kcompactd0:479] 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" Call Trace: __schedule schedule schedule_timeout wait_for_completion __flush_work __drain_all_pages __alloc_pages_slowpath.constprop.114 __alloc_pages alloc_migration_target migrate_pages migrate_to_node do_migrate_pages cpuset_migrate_mm_workfn process_one_work worker_thread kthread ret_from_fork
This failure is specific to CONFIG_PREEMPT=n builds. 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.
Link: https://lkml.kernel.org/r/20220203100326.GD3301@suse.de Fixes: d818fca1cac3 ("mm/vmscan: throttle reclaim and compaction when too may pages are isolated") Signed-off-by: Mel Gorman mgorman@suse.de Debugged-by: Vlastimil Babka vbabka@suse.cz Reviewed-by: Vlastimil Babka vbabka@suse.cz Acked-by: Michal Hocko mhocko@suse.com Acked-by: David Rientjes rientjes@google.com Cc: Hugh Dickins hughd@google.com Cc: Michal Hocko mhocko@suse.com Cc: Rik van Riel riel@surriel.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/vmscan.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
--- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1066,8 +1066,10 @@ void reclaim_throttle(pg_data_t *pgdat, * forward progress (e.g. journalling workqueues or kthreads). */ if (!current_is_kswapd() && - current->flags & (PF_IO_WORKER|PF_KTHREAD)) + current->flags & (PF_IO_WORKER|PF_KTHREAD)) { + cond_resched(); return; + }
/* * These figures are pulled out of thin air.