![Hugh Dickins](/assets/img/avatar_default.png)
A process spent 30 minutes exiting, just munlocking the pages of a large anonymous area that had been alternately mprotected into page-sized vmas: for every single page there's an anon_vma walk through all the other little vmas to find the right one. A general fix to that would be a lot more complicated (use prio_tree on anon_vma?), but there's one very simple thing we can do to speed up the common case: if a page to be munlocked is mapped only once, then it is our vma that it is mapped into, and there's no need whatever to walk through all the others. Okay, there is a very remote race in munlock_vma_pages_range(), if between its follow_page() and lock_page(), another process were to munlock the same page, then page reclaim remove it from our vma, then another process mlock it again. We would find it with page_mapcount 1, yet it's still mlocked in another process. But never mind, that's much less likely than the down_read_trylock() failure which munlocking already tolerates (in try_to_unmap_one()): in due course page reclaim will discover and move the page to unevictable instead. [akpm@linux-foundation.org: add comment] Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Michel Lespinasse <walken@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
626 lines
16 KiB
C
626 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 = SWAP_AGAIN;
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/*
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* Optimization: if the page was mapped just once,
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* that's our mapping and we don't need to check all the
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* other vmas.
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*/
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if (page_mapcount(page) > 1)
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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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/**
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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 | FOLL_MLOCK;
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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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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->mm))) {
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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, vm_flags_t 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->mm))
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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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vm_flags_t 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) {
|
|
vm_flags_t 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;
|
|
|
|
if (flags & MCL_CURRENT)
|
|
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);
|
|
}
|