During early boot (early_trace_init() called from start_kernel()), tracing allocates initial ring buffers (temp_buffer, array_buffer, and snapshot_buffer) for CPU 0. Later, as secondary CPUs come online during smp_init(), each CPU's ring buffer is allocated via trace_rb_cpu_prepare(). Before attempting page allocation, __rb_allocate_pages() performs a heuristic check using si_mem_available() to return early with -ENOMEM if memory appears insufficient. However, on kernels built with CONFIG_DEFERRED_STRUCT_PAGE_INIT=y, NR_FREE_PAGES only reflects the initial non-deferred pool across the entire period from early_trace_init() through smp_init(). defer_init() leaves only a single section per node (e.g. 16 MiB with 64 KB pages) initialized up-front, and on kernels with large static binary footprints (debug configurations enabling PAGE_OWNER, DEBUG_PAGEALLOC, KFENCE, or SLUB_DEBUG), early core initialisations (SLUB caches, vmalloc, static ftrace records) consume virtually all managed pages in this pool. si_mem_available() therefore returns a false negative (often 0-1 pages) across both SYSTEM_BOOTING (for the initial CPU 0 buffers) and SYSTEM_SCHEDULING (for secondary CPU buffers via trace_rb_cpu_prepare()), causing __rb_allocate_pages() to prematurely abort with -ENOMEM. This failure is false: the buddy allocator is designed to replenish ZONE_NORMAL on demand via deferred_grow_zone() when an actual allocation is attempted. Checking si_mem_available() before calling alloc_pages_node() short-circuits this on-demand growth entirely. deferred_grow_zone() is only permanently disabled after page_alloc_init_late() completes (it spawns per-node kthreads and blocks until done), which happens inside kernel_init_freeable() — before system_state is set to SYSTEM_FREEING_INITMEM. Skip the si_mem_available() check until SYSTEM_FREEING_INITMEM, at which point all deferred pages are initialized and si_mem_available() is accurate. Wrap the guard in #ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT so that on kernels without deferred init the original check is preserved unchanged. Fixes: 2a872fa4e9c8 ("ring-buffer: Check if memory is available before allocation") Cc: stable@vger.kernel.org Reported-by: Michal Suchánek Closes: https://lore.kernel.org/all/arYskzbiaNzBR9MD@kunlun.suse.cz/ Link: https://lore.kernel.org/all/arYskzbiaNzBR9MD@kunlun.suse.cz/ Signed-off-by: Amit Machhiwal --- Changes since v1: - Extend the guard to cover SYSTEM_SCHEDULING as well: smp_init() calls trace_rb_cpu_prepare() -> __rb_allocate_pages() before page_alloc_init_late() completes, so the false negative window spans both SYSTEM_BOOTING and SYSTEM_SCHEDULING. Use system_state >= SYSTEM_FREEING_INITMEM as the correct boundary. (Sashiko, Vincent Donnefort) - Wrap in #ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT to preserve the original check unchanged on non-deferred kernels. (Vincent Donnefort) - Drop Tested-by: guard condition changed, requesting fresh test. kernel/trace/ring_buffer.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 04bb94c29f58..aa877a272c89 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -2452,10 +2452,24 @@ static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer, * memory. It may not be accurate. But we don't care, we just want * to prevent doing any allocation when it is obvious that it is * not going to succeed. + * + * With CONFIG_DEFERRED_STRUCT_PAGE_INIT, NR_FREE_PAGES only reflects + * the initial non-deferred pool during early boot and throughout SMP + * bring-up (smp_init() runs before page_alloc_init_late() completes + * deferred initialization). si_mem_available() returns a false negative + * across this entire window while actual allocations succeed by growing + * the zone on demand via deferred_grow_zone(). Only re-enable the check + * from SYSTEM_FREEING_INITMEM onward, after page_alloc_init_late() has + * finished and si_mem_available() is accurate. */ i = si_mem_available(); +#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT + if (system_state >= SYSTEM_FREEING_INITMEM && i < nr_pages) + return -ENOMEM; +#else if (i < nr_pages) return -ENOMEM; +#endif /* * If a user thread allocates too much, and si_mem_available() base-commit: 2f2f7eeef8b0a1a9b9ca998231419873ccae8d4e -- 2.54.0 (Apple Git-157)