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McKenney" , Steven Rostedt , Masami Hiramatsu , Dennis Zhou , Tejun Heo , Christoph Lameter , Martin Liu , David Rientjes , christian.koenig@amd.com, Shakeel Butt , SeongJae Park , Michal Hocko , Johannes Weiner , Sweet Tea Dorminy , Lorenzo Stoakes , "Liam R . 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Many other > platforms aren't showing this, though we do have some other breakage in > -next which might be obscuring things. We get a NULL dereference: > > [ 2.481143] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 > > ... > > [ 2.485036] Call trace: > [ 2.485094] acct_account_cputime+0x40/0xa4 (P) > [ 2.485226] irqtime_account_process_tick+0x17c/0x1d8 > [ 2.485382] account_process_tick+0x12c/0x148 > [ 2.485531] update_process_times+0x28/0xdc > [ 2.485656] tick_nohz_handler+0xbc/0x1bc > [ 2.485809] __hrtimer_run_queues+0x130/0x184 > > I note that __acct_update_integrals is being called from here most > likely inline and doing get_mm_rss(). That uses get_mm_counter() which > we've updated in this patch, though I didn't spot the specific issue > yet. > There is something fishy in mm/init-mm.c:init_mm. The initialization of .cpu_bitmap = CPU_BITS_NONE, Keeps room for a NR_CPUs cpumask in that structure, but does not take into account the new extra room needed for mm_cid and the hierarchical per-cpu counters: in mm_cache_init() we have: mm_size = sizeof(struct mm_struct) + cpumask_size() + mm_cid_size() + get_rss_stat_items_size(); So AFAIU we should extend this end-of-mm size to include room for mm_cid_size() (2 * cpumask_size), which would be an upstream bug, and now room for get_rss_stat_items_size() (which is an issue specific to -next due to hierarchical per-cpu counters). An ugly work-around that may work (and then we can improve on this), at the end of mm/init-mm.c:init_mm (completely untested): .cpu_bitmap = { [0 ... ((3*BITS_TO_LONGS(NR_CPUS))-1 + ((69905 * NR_MM_COUNTERS * 64) / BYTES_PER_LONG))] = 0UL }, Thoughts ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com