From cdb2b590c159b1d6bcfe348a8f4243b1bc124064 Mon Sep 17 00:00:00 2001 From: Miaohe Lin Date: Thu, 9 Jun 2022 20:13:05 +0800 Subject: [PATCH] mm/memremap: fix memunmap_pages() race with get_dev_pagemap() [ Upstream commit 1e57ffb6e3fd9583268c6462c4e3853575b21701 ] Think about the below scene: CPU1 CPU2 memunmap_pages percpu_ref_exit __percpu_ref_exit free_percpu(percpu_count); /* percpu_count is freed here! */ get_dev_pagemap xa_load(&pgmap_array, PHYS_PFN(phys)) /* pgmap still in the pgmap_array */ percpu_ref_tryget_live(&pgmap->ref) if __ref_is_percpu /* __PERCPU_REF_ATOMIC_DEAD not set yet */ this_cpu_inc(*percpu_count) /* access freed percpu_count here! */ ref->percpu_count_ptr = __PERCPU_REF_ATOMIC_DEAD; /* too late... */ pageunmap_range To fix the issue, do percpu_ref_exit() after pgmap_array is emptied. So we won't do percpu_ref_tryget_live() against a being freed percpu_ref. Link: https://lkml.kernel.org/r/20220609121305.2508-1-linmiaohe@huawei.com Fixes: b7b3c01b1915 ("mm/memremap_pages: support multiple ranges per invocation") Signed-off-by: Miaohe Lin Cc: Dan Williams Signed-off-by: Andrew Morton Signed-off-by: Sasha Levin --- mm/memremap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/memremap.c b/mm/memremap.c index a638a27d89f5..8d743cbc2964 100644 --- a/mm/memremap.c +++ b/mm/memremap.c @@ -148,10 +148,10 @@ void memunmap_pages(struct dev_pagemap *pgmap) for_each_device_pfn(pfn, pgmap, i) put_page(pfn_to_page(pfn)); wait_for_completion(&pgmap->done); - percpu_ref_exit(&pgmap->ref); for (i = 0; i < pgmap->nr_range; i++) pageunmap_range(pgmap, i); + percpu_ref_exit(&pgmap->ref); WARN_ONCE(pgmap->altmap.alloc, "failed to free all reserved pages\n"); devmap_managed_enable_put(pgmap);