From: Dan Williams <dan.j.williams@xxxxxxxxx> Subject: mm: fix get_user_pages() vs device-dax pud mappings 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@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> Cc: Dave Jiang <dave.jiang@xxxxxxxxx> Cc: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx> Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Nilesh Choudhury <nilesh.choudhury@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- arch/x86/mm/gup.c | 28 ++++++++++++++++++++++++---- 1 file changed, 24 insertions(+), 4 deletions(-) diff -puN arch/x86/mm/gup.c~mm-fix-get_user_pages-vs-device-dax-pud-mappings arch/x86/mm/gup.c --- a/arch/x86/mm/gup.c~mm-fix-get_user_pages-vs-device-dax-pud-mappings +++ a/arch/x86/mm/gup.c @@ -154,14 +154,12 @@ static inline void get_head_page_multipl 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 p 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 p 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); _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
