Commit 018d2453 authored by Dennis Zhou's avatar Dennis Zhou Committed by Andrew Morton
Browse files

percpu: fix data race with pcpu_nr_empty_pop_pages 

Fixes the data race by moving the read to be behind the pcpu_lock. This
is okay because the code (initially) above it will not increase the
empty populated page count because it is populating backing pages that
already have allocations served out of them.

Link: https://lkml.kernel.org/r/20241008001942.8114-1-dennis@kernel.org


Reported-by: default avatarkernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202407191651.f24e499d-oliver.sang@intel.com


Signed-off-by: default avatarDennis Zhou <dennis@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent bd40b053

mm/percpu.c

+4 −3
Original line number Diff line number Diff line
@@ -1864,6 +1864,10 @@ void __percpu *pcpu_alloc_noprof(size_t size, size_t align, bool reserved, 


area_found:

	pcpu_stats_area_alloc(chunk, size);



	if (pcpu_nr_empty_pop_pages < PCPU_EMPTY_POP_PAGES_LOW)

		pcpu_schedule_balance_work();



	spin_unlock_irqrestore(&pcpu_lock, flags);



	/* populate if not all pages are already there */
@@ -1891,9 +1895,6 @@ void __percpu *pcpu_alloc_noprof(size_t size, size_t align, bool reserved, 
		mutex_unlock(&pcpu_alloc_mutex);

	}



	if (pcpu_nr_empty_pop_pages < PCPU_EMPTY_POP_PAGES_LOW)

		pcpu_schedule_balance_work();



	/* clear the areas and return address relative to base address */

	for_each_possible_cpu(cpu)

		memset((void *)pcpu_chunk_addr(chunk, cpu, 0) + off, 0, size);