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 usB2osh+ 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2025-12-18 13:00, Mark Brown wrote: > On Sat, Dec 13, 2025 at 01:56:07PM -0500, Mathieu Desnoyers wrote: > >> Use hierarchical per-cpu counters for rss tracking to fix the per-mm RSS >> tracking which has become too inaccurate for OOM killer purposes on >> large many-core systems. > > We're seeing boot time crashes in -next on the Arm FVP and Ampere Altra > which bisect to this patch which is commit 240587b6cca2822d. 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