mm: fix bad rss-counter if remap_file_pages raced migration (88784396) · Commits · 戴 / test

Fix some "Bad rss-counter state" reports on exit, arising from the interaction between page migration and remap_file_pages(): zap_pte() must count a migration entry when zapping it. And yes, it is possible (though very unusual) to find an anon page or swap entry in a VM_SHARED nonlinear mapping: coming from that horrid get_user_pages(write, force) case which COWs even in a shared mapping. Signed-off-by:

Hugh Dickins <hughd@google.com> Tested-by:

Sasha Levin <sasha.levin@oracle.com> Tested-by:

Dave Jones <davej@redhat.com> Cc: Cyrill Gorcunov <gorcunov@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/fremap.c

+22 −6

Original line number	Diff line number	Diff line
		@@ -23,28 +23,44 @@

		#include "internal.h"

		static int mm_counter(struct page *page)
		{
		return PageAnon(page) ? MM_ANONPAGES : MM_FILEPAGES;
		}

		static void zap_pte(struct mm_struct mm, struct vm_area_struct vma,
		unsigned long addr, pte_t *ptep)
		{
		pte_t pte = *ptep;

		if (pte_present(pte)) {
		struct page *page;
		swp_entry_t entry;

		if (pte_present(pte)) {
		flush_cache_page(vma, addr, pte_pfn(pte));
		pte = ptep_clear_flush(vma, addr, ptep);
		page = vm_normal_page(vma, addr, pte);
		if (page) {
		if (pte_dirty(pte))
		set_page_dirty(page);
		update_hiwater_rss(mm);
		dec_mm_counter(mm, mm_counter(page));
		page_remove_rmap(page);
		page_cache_release(page);
		}
		} else { /* zap_pte() is not called when pte_none() */
		if (!pte_file(pte)) {
		update_hiwater_rss(mm);
		dec_mm_counter(mm, MM_FILEPAGES);
		entry = pte_to_swp_entry(pte);
		if (non_swap_entry(entry)) {
		if (is_migration_entry(entry)) {
		page = migration_entry_to_page(entry);
		dec_mm_counter(mm, mm_counter(page));
		}
		} else {
		if (!pte_file(pte))
		free_swap_and_cache(pte_to_swp_entry(pte));
		free_swap_and_cache(entry);
		dec_mm_counter(mm, MM_SWAPENTS);
		}
		}
		pte_clear_not_present_full(mm, addr, ptep, 0);
		}
		}

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