mm: fix get_user_pages() vs device-dax pud mappings (220ced16) · Commits · 戴 / test

A new unit test for the device-dax 1GB enabling currently fails with this warning before hanging the test thread: WARNING: CPU: 0 PID: 21 at lib/percpu-refcount.c:155 percpu_ref_switch_to_atomic_rcu+0x1e3/0x1f0 percpu ref (dax_pmem_percpu_release [dax_pmem]) <= 0 (0) after switching to atomic [..] CPU: 0 PID: 21 Comm: rcuos/1 Tainted: G O 4.10.0-rc7-next-20170207+ #944 [..] Call Trace: dump_stack+0x86/0xc3 __warn+0xcb/0xf0 warn_slowpath_fmt+0x5f/0x80 ? rcu_nocb_kthread+0x27a/0x510 ? dax_pmem_percpu_exit+0x50/0x50 [dax_pmem] percpu_ref_switch_to_atomic_rcu+0x1e3/0x1f0 ? percpu_ref_exit+0x60/0x60 rcu_nocb_kthread+0x339/0x510 ? rcu_nocb_kthread+0x27a/0x510 kthread+0x101/0x140 The get_user_pages() path needs to arrange for references to be taken against the dev_pagemap instance backing the pud mapping. Refactor the existing __gup_device_huge_pmd() to also account for the pud case. Link: http://lkml.kernel.org/r/148653181153.38226.9605457830505509385.stgit@dwillia2-desk3.amr.corp.intel.com Signed-off-by:

Dan Williams <dan.j.williams@intel.com> Cc: Dave Jiang <dave.jiang@intel.com> Cc: Matthew Wilcox <mawilcox@microsoft.com> Cc: Ross Zwisler <ross.zwisler@linux.intel.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Nilesh Choudhury <nilesh.choudhury@oracle.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

arch/x86/mm/gup.c

+24 −4

Original line number	Diff line number	Diff line
		@@ -154,14 +154,12 @@ static inline void get_head_page_multiple(struct page *page, int nr)
		SetPageReferenced(page);
		}

		static int __gup_device_huge_pmd(pmd_t pmd, unsigned long addr,
		static int __gup_device_huge(unsigned long pfn, unsigned long addr,
		unsigned long end, struct page *pages, int nr)
		{
		int nr_start = *nr;
		unsigned long pfn = pmd_pfn(pmd);
		struct dev_pagemap *pgmap = NULL;

		pfn += (addr & ~PMD_MASK) >> PAGE_SHIFT;
		do {
		struct page *page = pfn_to_page(pfn);

		@@ -180,6 +178,24 @@ static int __gup_device_huge_pmd(pmd_t pmd, unsigned long addr,
		return 1;
		}

		static int __gup_device_huge_pmd(pmd_t pmd, unsigned long addr,
		unsigned long end, struct page *pages, int nr)
		{
		unsigned long fault_pfn;

		fault_pfn = pmd_pfn(pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
		return __gup_device_huge(fault_pfn, addr, end, pages, nr);
		}

		static int __gup_device_huge_pud(pud_t pud, unsigned long addr,
		unsigned long end, struct page *pages, int nr)
		{
		unsigned long fault_pfn;

		fault_pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
		return __gup_device_huge(fault_pfn, addr, end, pages, nr);
		}

		static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr,
		unsigned long end, int write, struct page *pages, int nr)
		{
		@@ -251,9 +267,13 @@ static noinline int gup_huge_pud(pud_t pud, unsigned long addr,

		if (!pte_allows_gup(pud_val(pud), write))
		return 0;

		VM_BUG_ON(!pfn_valid(pud_pfn(pud)));
		if (pud_devmap(pud))
		return __gup_device_huge_pud(pud, addr, end, pages, nr);

		/* hugepages are never "special" */
		VM_BUG_ON(pud_flags(pud) & _PAGE_SPECIAL);
		VM_BUG_ON(!pfn_valid(pud_pfn(pud)));

		refs = 0;
		head = pud_page(pud);

Admin message