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![Michel Lespinasse](/assets/img/avatar_default.png)
As Tao Ma noticed, change5ecfda0
breaks blktrace. This is because blktrace mmaps a file with PROT_WRITE permissions but without PROT_READ, so my attempt to not unnecessarity break COW during mlock ended up causing mlock to fail with a permission problem. I am proposing to let mlock ignore vma protection in all cases except PROT_NONE. In particular, mlock should not fail for PROT_WRITE regions (as in the blktrace case, which broke at5ecfda0
) or for PROT_EXEC regions (which seem to me like they were always broken). Signed-off-by: Michel Lespinasse <walken@google.com> Acked-by: Rik van Riel <riel@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
632 lines
16 KiB
C
632 lines
16 KiB
C
/*
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* linux/mm/mlock.c
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*
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* (C) Copyright 1995 Linus Torvalds
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* (C) Copyright 2002 Christoph Hellwig
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*/
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#include <linux/capability.h>
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#include <linux/mman.h>
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#include <linux/mm.h>
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#include <linux/swap.h>
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#include <linux/swapops.h>
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#include <linux/pagemap.h>
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#include <linux/mempolicy.h>
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#include <linux/syscalls.h>
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#include <linux/sched.h>
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#include <linux/module.h>
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#include <linux/rmap.h>
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#include <linux/mmzone.h>
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#include <linux/hugetlb.h>
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#include "internal.h"
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int can_do_mlock(void)
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{
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if (capable(CAP_IPC_LOCK))
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return 1;
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if (rlimit(RLIMIT_MEMLOCK) != 0)
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return 1;
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return 0;
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}
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EXPORT_SYMBOL(can_do_mlock);
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/*
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* Mlocked pages are marked with PageMlocked() flag for efficient testing
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* in vmscan and, possibly, the fault path; and to support semi-accurate
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* statistics.
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*
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* An mlocked page [PageMlocked(page)] is unevictable. As such, it will
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* be placed on the LRU "unevictable" list, rather than the [in]active lists.
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* The unevictable list is an LRU sibling list to the [in]active lists.
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* PageUnevictable is set to indicate the unevictable state.
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*
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* When lazy mlocking via vmscan, it is important to ensure that the
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* vma's VM_LOCKED status is not concurrently being modified, otherwise we
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* may have mlocked a page that is being munlocked. So lazy mlock must take
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* the mmap_sem for read, and verify that the vma really is locked
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* (see mm/rmap.c).
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*/
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/*
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* LRU accounting for clear_page_mlock()
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*/
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void __clear_page_mlock(struct page *page)
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{
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VM_BUG_ON(!PageLocked(page));
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if (!page->mapping) { /* truncated ? */
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return;
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}
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dec_zone_page_state(page, NR_MLOCK);
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count_vm_event(UNEVICTABLE_PGCLEARED);
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if (!isolate_lru_page(page)) {
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putback_lru_page(page);
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} else {
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/*
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* We lost the race. the page already moved to evictable list.
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*/
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if (PageUnevictable(page))
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count_vm_event(UNEVICTABLE_PGSTRANDED);
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}
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}
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/*
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* Mark page as mlocked if not already.
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* If page on LRU, isolate and putback to move to unevictable list.
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*/
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void mlock_vma_page(struct page *page)
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{
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BUG_ON(!PageLocked(page));
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if (!TestSetPageMlocked(page)) {
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inc_zone_page_state(page, NR_MLOCK);
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count_vm_event(UNEVICTABLE_PGMLOCKED);
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if (!isolate_lru_page(page))
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putback_lru_page(page);
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}
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}
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/**
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* munlock_vma_page - munlock a vma page
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* @page - page to be unlocked
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*
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* called from munlock()/munmap() path with page supposedly on the LRU.
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* When we munlock a page, because the vma where we found the page is being
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* munlock()ed or munmap()ed, we want to check whether other vmas hold the
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* page locked so that we can leave it on the unevictable lru list and not
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* bother vmscan with it. However, to walk the page's rmap list in
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* try_to_munlock() we must isolate the page from the LRU. If some other
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* task has removed the page from the LRU, we won't be able to do that.
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* So we clear the PageMlocked as we might not get another chance. If we
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* can't isolate the page, we leave it for putback_lru_page() and vmscan
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* [page_referenced()/try_to_unmap()] to deal with.
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*/
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void munlock_vma_page(struct page *page)
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{
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BUG_ON(!PageLocked(page));
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if (TestClearPageMlocked(page)) {
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dec_zone_page_state(page, NR_MLOCK);
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if (!isolate_lru_page(page)) {
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int ret = try_to_munlock(page);
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/*
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* did try_to_unlock() succeed or punt?
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*/
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if (ret != SWAP_MLOCK)
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count_vm_event(UNEVICTABLE_PGMUNLOCKED);
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putback_lru_page(page);
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} else {
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/*
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* Some other task has removed the page from the LRU.
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* putback_lru_page() will take care of removing the
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* page from the unevictable list, if necessary.
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* vmscan [page_referenced()] will move the page back
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* to the unevictable list if some other vma has it
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* mlocked.
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*/
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if (PageUnevictable(page))
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count_vm_event(UNEVICTABLE_PGSTRANDED);
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else
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count_vm_event(UNEVICTABLE_PGMUNLOCKED);
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}
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}
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}
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static inline int stack_guard_page(struct vm_area_struct *vma, unsigned long addr)
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{
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return (vma->vm_flags & VM_GROWSDOWN) &&
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(vma->vm_start == addr) &&
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!vma_stack_continue(vma->vm_prev, addr);
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}
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/**
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* __mlock_vma_pages_range() - mlock a range of pages in the vma.
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* @vma: target vma
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* @start: start address
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* @end: end address
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*
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* This takes care of making the pages present too.
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*
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* return 0 on success, negative error code on error.
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*
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* vma->vm_mm->mmap_sem must be held for at least read.
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*/
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static long __mlock_vma_pages_range(struct vm_area_struct *vma,
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unsigned long start, unsigned long end,
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int *nonblocking)
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{
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struct mm_struct *mm = vma->vm_mm;
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unsigned long addr = start;
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int nr_pages = (end - start) / PAGE_SIZE;
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int gup_flags;
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VM_BUG_ON(start & ~PAGE_MASK);
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VM_BUG_ON(end & ~PAGE_MASK);
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VM_BUG_ON(start < vma->vm_start);
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VM_BUG_ON(end > vma->vm_end);
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VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
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gup_flags = FOLL_TOUCH;
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/*
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* We want to touch writable mappings with a write fault in order
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* to break COW, except for shared mappings because these don't COW
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* and we would not want to dirty them for nothing.
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*/
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if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
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gup_flags |= FOLL_WRITE;
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/*
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* We want mlock to succeed for regions that have any permissions
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* other than PROT_NONE.
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*/
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if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC))
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gup_flags |= FOLL_FORCE;
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if (vma->vm_flags & VM_LOCKED)
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gup_flags |= FOLL_MLOCK;
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/* We don't try to access the guard page of a stack vma */
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if (stack_guard_page(vma, start)) {
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addr += PAGE_SIZE;
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nr_pages--;
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}
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return __get_user_pages(current, mm, addr, nr_pages, gup_flags,
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NULL, NULL, nonblocking);
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}
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/*
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* convert get_user_pages() return value to posix mlock() error
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*/
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static int __mlock_posix_error_return(long retval)
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{
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if (retval == -EFAULT)
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retval = -ENOMEM;
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else if (retval == -ENOMEM)
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retval = -EAGAIN;
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return retval;
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}
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/**
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* mlock_vma_pages_range() - mlock pages in specified vma range.
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* @vma - the vma containing the specfied address range
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* @start - starting address in @vma to mlock
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* @end - end address [+1] in @vma to mlock
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*
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* For mmap()/mremap()/expansion of mlocked vma.
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*
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* return 0 on success for "normal" vmas.
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*
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* return number of pages [> 0] to be removed from locked_vm on success
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* of "special" vmas.
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*/
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long mlock_vma_pages_range(struct vm_area_struct *vma,
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unsigned long start, unsigned long end)
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{
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int nr_pages = (end - start) / PAGE_SIZE;
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BUG_ON(!(vma->vm_flags & VM_LOCKED));
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/*
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* filter unlockable vmas
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*/
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if (vma->vm_flags & (VM_IO | VM_PFNMAP))
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goto no_mlock;
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if (!((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
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is_vm_hugetlb_page(vma) ||
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vma == get_gate_vma(current))) {
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__mlock_vma_pages_range(vma, start, end, NULL);
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/* Hide errors from mmap() and other callers */
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return 0;
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}
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/*
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* User mapped kernel pages or huge pages:
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* make these pages present to populate the ptes, but
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* fall thru' to reset VM_LOCKED--no need to unlock, and
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* return nr_pages so these don't get counted against task's
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* locked limit. huge pages are already counted against
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* locked vm limit.
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*/
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make_pages_present(start, end);
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no_mlock:
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vma->vm_flags &= ~VM_LOCKED; /* and don't come back! */
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return nr_pages; /* error or pages NOT mlocked */
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}
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/*
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* munlock_vma_pages_range() - munlock all pages in the vma range.'
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* @vma - vma containing range to be munlock()ed.
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* @start - start address in @vma of the range
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* @end - end of range in @vma.
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*
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* For mremap(), munmap() and exit().
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*
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* Called with @vma VM_LOCKED.
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*
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* Returns with VM_LOCKED cleared. Callers must be prepared to
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* deal with this.
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*
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* We don't save and restore VM_LOCKED here because pages are
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* still on lru. In unmap path, pages might be scanned by reclaim
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* and re-mlocked by try_to_{munlock|unmap} before we unmap and
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* free them. This will result in freeing mlocked pages.
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*/
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void munlock_vma_pages_range(struct vm_area_struct *vma,
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unsigned long start, unsigned long end)
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{
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unsigned long addr;
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lru_add_drain();
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vma->vm_flags &= ~VM_LOCKED;
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for (addr = start; addr < end; addr += PAGE_SIZE) {
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struct page *page;
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/*
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* Although FOLL_DUMP is intended for get_dump_page(),
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* it just so happens that its special treatment of the
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* ZERO_PAGE (returning an error instead of doing get_page)
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* suits munlock very well (and if somehow an abnormal page
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* has sneaked into the range, we won't oops here: great).
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*/
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page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
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if (page && !IS_ERR(page)) {
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lock_page(page);
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/*
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* Like in __mlock_vma_pages_range(),
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* because we lock page here and migration is
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* blocked by the elevated reference, we need
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* only check for file-cache page truncation.
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*/
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if (page->mapping)
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munlock_vma_page(page);
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unlock_page(page);
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put_page(page);
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}
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cond_resched();
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}
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}
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/*
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* mlock_fixup - handle mlock[all]/munlock[all] requests.
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*
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* Filters out "special" vmas -- VM_LOCKED never gets set for these, and
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* munlock is a no-op. However, for some special vmas, we go ahead and
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* populate the ptes via make_pages_present().
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*
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* For vmas that pass the filters, merge/split as appropriate.
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*/
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static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
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unsigned long start, unsigned long end, unsigned int newflags)
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{
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struct mm_struct *mm = vma->vm_mm;
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pgoff_t pgoff;
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int nr_pages;
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int ret = 0;
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int lock = newflags & VM_LOCKED;
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if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) ||
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is_vm_hugetlb_page(vma) || vma == get_gate_vma(current))
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goto out; /* don't set VM_LOCKED, don't count */
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pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
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*prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
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vma->vm_file, pgoff, vma_policy(vma));
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if (*prev) {
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vma = *prev;
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goto success;
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}
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if (start != vma->vm_start) {
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ret = split_vma(mm, vma, start, 1);
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if (ret)
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goto out;
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}
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if (end != vma->vm_end) {
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ret = split_vma(mm, vma, end, 0);
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if (ret)
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goto out;
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}
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success:
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/*
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* Keep track of amount of locked VM.
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*/
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nr_pages = (end - start) >> PAGE_SHIFT;
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if (!lock)
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nr_pages = -nr_pages;
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mm->locked_vm += nr_pages;
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/*
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* vm_flags is protected by the mmap_sem held in write mode.
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* It's okay if try_to_unmap_one unmaps a page just after we
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* set VM_LOCKED, __mlock_vma_pages_range will bring it back.
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*/
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if (lock)
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vma->vm_flags = newflags;
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else
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munlock_vma_pages_range(vma, start, end);
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out:
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*prev = vma;
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return ret;
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}
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static int do_mlock(unsigned long start, size_t len, int on)
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{
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unsigned long nstart, end, tmp;
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struct vm_area_struct * vma, * prev;
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int error;
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VM_BUG_ON(start & ~PAGE_MASK);
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VM_BUG_ON(len != PAGE_ALIGN(len));
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end = start + len;
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if (end < start)
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return -EINVAL;
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if (end == start)
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return 0;
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vma = find_vma_prev(current->mm, start, &prev);
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if (!vma || vma->vm_start > start)
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return -ENOMEM;
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if (start > vma->vm_start)
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prev = vma;
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for (nstart = start ; ; ) {
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unsigned int newflags;
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/* Here we know that vma->vm_start <= nstart < vma->vm_end. */
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newflags = vma->vm_flags | VM_LOCKED;
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if (!on)
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newflags &= ~VM_LOCKED;
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tmp = vma->vm_end;
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if (tmp > end)
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tmp = end;
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error = mlock_fixup(vma, &prev, nstart, tmp, newflags);
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if (error)
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break;
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nstart = tmp;
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if (nstart < prev->vm_end)
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nstart = prev->vm_end;
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if (nstart >= end)
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break;
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vma = prev->vm_next;
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if (!vma || vma->vm_start != nstart) {
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error = -ENOMEM;
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break;
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}
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}
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return error;
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}
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static int do_mlock_pages(unsigned long start, size_t len, int ignore_errors)
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{
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struct mm_struct *mm = current->mm;
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unsigned long end, nstart, nend;
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struct vm_area_struct *vma = NULL;
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int locked = 0;
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int ret = 0;
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VM_BUG_ON(start & ~PAGE_MASK);
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VM_BUG_ON(len != PAGE_ALIGN(len));
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end = start + len;
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for (nstart = start; nstart < end; nstart = nend) {
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/*
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* We want to fault in pages for [nstart; end) address range.
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* Find first corresponding VMA.
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*/
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if (!locked) {
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locked = 1;
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down_read(&mm->mmap_sem);
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vma = find_vma(mm, nstart);
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} else if (nstart >= vma->vm_end)
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vma = vma->vm_next;
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if (!vma || vma->vm_start >= end)
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break;
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/*
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* Set [nstart; nend) to intersection of desired address
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* range with the first VMA. Also, skip undesirable VMA types.
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*/
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nend = min(end, vma->vm_end);
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if (vma->vm_flags & (VM_IO | VM_PFNMAP))
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continue;
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if (nstart < vma->vm_start)
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nstart = vma->vm_start;
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/*
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* Now fault in a range of pages. __mlock_vma_pages_range()
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* double checks the vma flags, so that it won't mlock pages
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* if the vma was already munlocked.
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*/
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ret = __mlock_vma_pages_range(vma, nstart, nend, &locked);
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if (ret < 0) {
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if (ignore_errors) {
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ret = 0;
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continue; /* continue at next VMA */
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}
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ret = __mlock_posix_error_return(ret);
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break;
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}
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nend = nstart + ret * PAGE_SIZE;
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ret = 0;
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}
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if (locked)
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up_read(&mm->mmap_sem);
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return ret; /* 0 or negative error code */
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}
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SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
|
|
{
|
|
unsigned long locked;
|
|
unsigned long lock_limit;
|
|
int error = -ENOMEM;
|
|
|
|
if (!can_do_mlock())
|
|
return -EPERM;
|
|
|
|
lru_add_drain_all(); /* flush pagevec */
|
|
|
|
down_write(¤t->mm->mmap_sem);
|
|
len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
|
|
start &= PAGE_MASK;
|
|
|
|
locked = len >> PAGE_SHIFT;
|
|
locked += current->mm->locked_vm;
|
|
|
|
lock_limit = rlimit(RLIMIT_MEMLOCK);
|
|
lock_limit >>= PAGE_SHIFT;
|
|
|
|
/* check against resource limits */
|
|
if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
|
|
error = do_mlock(start, len, 1);
|
|
up_write(¤t->mm->mmap_sem);
|
|
if (!error)
|
|
error = do_mlock_pages(start, len, 0);
|
|
return error;
|
|
}
|
|
|
|
SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
|
|
{
|
|
int ret;
|
|
|
|
down_write(¤t->mm->mmap_sem);
|
|
len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
|
|
start &= PAGE_MASK;
|
|
ret = do_mlock(start, len, 0);
|
|
up_write(¤t->mm->mmap_sem);
|
|
return ret;
|
|
}
|
|
|
|
static int do_mlockall(int flags)
|
|
{
|
|
struct vm_area_struct * vma, * prev = NULL;
|
|
unsigned int def_flags = 0;
|
|
|
|
if (flags & MCL_FUTURE)
|
|
def_flags = VM_LOCKED;
|
|
current->mm->def_flags = def_flags;
|
|
if (flags == MCL_FUTURE)
|
|
goto out;
|
|
|
|
for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {
|
|
unsigned int newflags;
|
|
|
|
newflags = vma->vm_flags | VM_LOCKED;
|
|
if (!(flags & MCL_CURRENT))
|
|
newflags &= ~VM_LOCKED;
|
|
|
|
/* Ignore errors */
|
|
mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
|
|
}
|
|
out:
|
|
return 0;
|
|
}
|
|
|
|
SYSCALL_DEFINE1(mlockall, int, flags)
|
|
{
|
|
unsigned long lock_limit;
|
|
int ret = -EINVAL;
|
|
|
|
if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE)))
|
|
goto out;
|
|
|
|
ret = -EPERM;
|
|
if (!can_do_mlock())
|
|
goto out;
|
|
|
|
lru_add_drain_all(); /* flush pagevec */
|
|
|
|
down_write(¤t->mm->mmap_sem);
|
|
|
|
lock_limit = rlimit(RLIMIT_MEMLOCK);
|
|
lock_limit >>= PAGE_SHIFT;
|
|
|
|
ret = -ENOMEM;
|
|
if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
|
|
capable(CAP_IPC_LOCK))
|
|
ret = do_mlockall(flags);
|
|
up_write(¤t->mm->mmap_sem);
|
|
if (!ret && (flags & MCL_CURRENT)) {
|
|
/* Ignore errors */
|
|
do_mlock_pages(0, TASK_SIZE, 1);
|
|
}
|
|
out:
|
|
return ret;
|
|
}
|
|
|
|
SYSCALL_DEFINE0(munlockall)
|
|
{
|
|
int ret;
|
|
|
|
down_write(¤t->mm->mmap_sem);
|
|
ret = do_mlockall(0);
|
|
up_write(¤t->mm->mmap_sem);
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
|
|
* shm segments) get accounted against the user_struct instead.
|
|
*/
|
|
static DEFINE_SPINLOCK(shmlock_user_lock);
|
|
|
|
int user_shm_lock(size_t size, struct user_struct *user)
|
|
{
|
|
unsigned long lock_limit, locked;
|
|
int allowed = 0;
|
|
|
|
locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
|
|
lock_limit = rlimit(RLIMIT_MEMLOCK);
|
|
if (lock_limit == RLIM_INFINITY)
|
|
allowed = 1;
|
|
lock_limit >>= PAGE_SHIFT;
|
|
spin_lock(&shmlock_user_lock);
|
|
if (!allowed &&
|
|
locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
|
|
goto out;
|
|
get_uid(user);
|
|
user->locked_shm += locked;
|
|
allowed = 1;
|
|
out:
|
|
spin_unlock(&shmlock_user_lock);
|
|
return allowed;
|
|
}
|
|
|
|
void user_shm_unlock(size_t size, struct user_struct *user)
|
|
{
|
|
spin_lock(&shmlock_user_lock);
|
|
user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
|
|
spin_unlock(&shmlock_user_lock);
|
|
free_uid(user);
|
|
}
|