mlock: downgrade mmap sem while populating mlocked regions

[linux-2.6/mini2440.git] / mm / mlock.c

/*
 *      linux/mm/mlock.c
 *
 *  (C) Copyright 1995 Linus Torvalds
 *  (C) Copyright 2002 Christoph Hellwig
 */

#include <linux/capability.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/pagemap.h>
#include <linux/mempolicy.h>
#include <linux/syscalls.h>
#include <linux/sched.h>
#include <linux/module.h>
#include <linux/rmap.h>
#include <linux/mmzone.h>
#include <linux/hugetlb.h>

#include "internal.h"

int can_do_mlock(void)
{
        if (capable(CAP_IPC_LOCK))
                return 1;
        if (current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur != 0)
                return 1;
        return 0;
}
EXPORT_SYMBOL(can_do_mlock);

#ifdef CONFIG_UNEVICTABLE_LRU
/*
 * Mlocked pages are marked with PageMlocked() flag for efficient testing
 * in vmscan and, possibly, the fault path; and to support semi-accurate
 * statistics.
 *
 * An mlocked page [PageMlocked(page)] is unevictable.  As such, it will
 * be placed on the LRU "unevictable" list, rather than the [in]active lists.
 * The unevictable list is an LRU sibling list to the [in]active lists.
 * PageUnevictable is set to indicate the unevictable state.
 *
 * When lazy mlocking via vmscan, it is important to ensure that the
 * vma's VM_LOCKED status is not concurrently being modified, otherwise we
 * may have mlocked a page that is being munlocked. So lazy mlock must take
 * the mmap_sem for read, and verify that the vma really is locked
 * (see mm/rmap.c).
 */

/*
 *  LRU accounting for clear_page_mlock()
 */
void __clear_page_mlock(struct page *page)
{
        VM_BUG_ON(!PageLocked(page));

        if (!page->mapping) {   /* truncated ? */
                return;
        }

        if (!isolate_lru_page(page)) {
                putback_lru_page(page);
        } else {
                /*
                 * Page not on the LRU yet.  Flush all pagevecs and retry.
                 */
                lru_add_drain_all();
                if (!isolate_lru_page(page))
                        putback_lru_page(page);
        }
}

/*
 * Mark page as mlocked if not already.
 * If page on LRU, isolate and putback to move to unevictable list.
 */
void mlock_vma_page(struct page *page)
{
        BUG_ON(!PageLocked(page));

        if (!TestSetPageMlocked(page) && !isolate_lru_page(page))
                putback_lru_page(page);
}

/*
 * called from munlock()/munmap() path with page supposedly on the LRU.
 *
 * Note:  unlike mlock_vma_page(), we can't just clear the PageMlocked
 * [in try_to_munlock()] and then attempt to isolate the page.  We must
 * isolate the page to keep others from messing with its unevictable
 * and mlocked state while trying to munlock.  However, we pre-clear the
 * mlocked state anyway as we might lose the isolation race and we might
 * not get another chance to clear PageMlocked.  If we successfully
 * isolate the page and try_to_munlock() detects other VM_LOCKED vmas
 * mapping the page, it will restore the PageMlocked state, unless the page
 * is mapped in a non-linear vma.  So, we go ahead and SetPageMlocked(),
 * perhaps redundantly.
 * If we lose the isolation race, and the page is mapped by other VM_LOCKED
 * vmas, we'll detect this in vmscan--via try_to_munlock() or try_to_unmap()
 * either of which will restore the PageMlocked state by calling
 * mlock_vma_page() above, if it can grab the vma's mmap sem.
 */
static void munlock_vma_page(struct page *page)
{
        BUG_ON(!PageLocked(page));

        if (TestClearPageMlocked(page) && !isolate_lru_page(page)) {
                try_to_munlock(page);
                putback_lru_page(page);
        }
}

/*
 * mlock a range of pages in the vma.
 *
 * This takes care of making the pages present too.
 *
 * vma->vm_mm->mmap_sem must be held for write.
 */
static int __mlock_vma_pages_range(struct vm_area_struct *vma,
                        unsigned long start, unsigned long end)
{
        struct mm_struct *mm = vma->vm_mm;
        unsigned long addr = start;
        struct page *pages[16]; /* 16 gives a reasonable batch */
        int write = !!(vma->vm_flags & VM_WRITE);
        int nr_pages = (end - start) / PAGE_SIZE;
        int ret;

        VM_BUG_ON(start & ~PAGE_MASK || end & ~PAGE_MASK);
        VM_BUG_ON(start < vma->vm_start || end > vma->vm_end);
        VM_BUG_ON(!rwsem_is_locked(&vma->vm_mm->mmap_sem));

        lru_add_drain_all();    /* push cached pages to LRU */

        while (nr_pages > 0) {
                int i;

                cond_resched();

                /*
                 * get_user_pages makes pages present if we are
                 * setting mlock. and this extra reference count will
                 * disable migration of this page.  However, page may
                 * still be truncated out from under us.
                 */
                ret = get_user_pages(current, mm, addr,
                                min_t(int, nr_pages, ARRAY_SIZE(pages)),
                                write, 0, pages, NULL);
                /*
                 * This can happen for, e.g., VM_NONLINEAR regions before
                 * a page has been allocated and mapped at a given offset,
                 * or for addresses that map beyond end of a file.
                 * We'll mlock the the pages if/when they get faulted in.
                 */
                if (ret < 0)
                        break;
                if (ret == 0) {
                        /*
                         * We know the vma is there, so the only time
                         * we cannot get a single page should be an
                         * error (ret < 0) case.
                         */
                        WARN_ON(1);
                        break;
                }

                lru_add_drain();        /* push cached pages to LRU */

                for (i = 0; i < ret; i++) {
                        struct page *page = pages[i];

                        lock_page(page);
                        /*
                         * Because we lock page here and migration is blocked
                         * by the elevated reference, we need only check for
                         * page truncation (file-cache only).
                         */
                        if (page->mapping)
                                mlock_vma_page(page);
                        unlock_page(page);
                        put_page(page);         /* ref from get_user_pages() */

                        /*
                         * here we assume that get_user_pages() has given us
                         * a list of virtually contiguous pages.
                         */
                        addr += PAGE_SIZE;      /* for next get_user_pages() */
                        nr_pages--;
                }
        }

        lru_add_drain_all();    /* to update stats */

        return 0;       /* count entire vma as locked_vm */
}

/*
 * private structure for munlock page table walk
 */
struct munlock_page_walk {
        struct vm_area_struct *vma;
        pmd_t                 *pmd; /* for migration_entry_wait() */
};

/*
 * munlock normal pages for present ptes
 */
static int __munlock_pte_handler(pte_t *ptep, unsigned long addr,
                                   unsigned long end, struct mm_walk *walk)
{
        struct munlock_page_walk *mpw = walk->private;
        swp_entry_t entry;
        struct page *page;
        pte_t pte;

retry:
        pte = *ptep;
        /*
         * If it's a swap pte, we might be racing with page migration.
         */
        if (unlikely(!pte_present(pte))) {
                if (!is_swap_pte(pte))
                        goto out;
                entry = pte_to_swp_entry(pte);
                if (is_migration_entry(entry)) {
                        migration_entry_wait(mpw->vma->vm_mm, mpw->pmd, addr);
                        goto retry;
                }
                goto out;
        }

        page = vm_normal_page(mpw->vma, addr, pte);
        if (!page)
                goto out;

        lock_page(page);
        if (!page->mapping) {
                unlock_page(page);
                goto retry;
        }
        munlock_vma_page(page);
        unlock_page(page);

out:
        return 0;
}

/*
 * Save pmd for pte handler for waiting on migration entries
 */
static int __munlock_pmd_handler(pmd_t *pmd, unsigned long addr,
                                 unsigned long end, struct mm_walk *walk)
{
        struct munlock_page_walk *mpw = walk->private;

        mpw->pmd = pmd;
        return 0;
}


/*
 * munlock a range of pages in the vma using standard page table walk.
 *
 * vma->vm_mm->mmap_sem must be held for write.
 */
static void __munlock_vma_pages_range(struct vm_area_struct *vma,
                              unsigned long start, unsigned long end)
{
        struct mm_struct *mm = vma->vm_mm;
        struct munlock_page_walk mpw = {
                .vma = vma,
        };
        struct mm_walk munlock_page_walk = {
                .pmd_entry = __munlock_pmd_handler,
                .pte_entry = __munlock_pte_handler,
                .private = &mpw,
                .mm = mm,
        };

        VM_BUG_ON(start & ~PAGE_MASK || end & ~PAGE_MASK);
        VM_BUG_ON(!rwsem_is_locked(&vma->vm_mm->mmap_sem));
        VM_BUG_ON(start < vma->vm_start);
        VM_BUG_ON(end > vma->vm_end);

        lru_add_drain_all();    /* push cached pages to LRU */
        walk_page_range(start, end, &munlock_page_walk);
        lru_add_drain_all();    /* to update stats */
}

#else /* CONFIG_UNEVICTABLE_LRU */

/*
 * Just make pages present if VM_LOCKED.  No-op if unlocking.
 */
static int __mlock_vma_pages_range(struct vm_area_struct *vma,
                        unsigned long start, unsigned long end)
{
        if (vma->vm_flags & VM_LOCKED)
                make_pages_present(start, end);
        return 0;
}

/*
 * munlock a range of pages in the vma -- no-op.
 */
static void __munlock_vma_pages_range(struct vm_area_struct *vma,
                              unsigned long start, unsigned long end)
{
}
#endif /* CONFIG_UNEVICTABLE_LRU */

/*
 * mlock all pages in this vma range.  For mmap()/mremap()/...
 */
int mlock_vma_pages_range(struct vm_area_struct *vma,
                        unsigned long start, unsigned long end)
{
        struct mm_struct *mm = vma->vm_mm;
        int nr_pages = (end - start) / PAGE_SIZE;
        BUG_ON(!(vma->vm_flags & VM_LOCKED));

        /*
         * filter unlockable vmas
         */
        if (vma->vm_flags & (VM_IO | VM_PFNMAP))
                goto no_mlock;

        if (!((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
                        is_vm_hugetlb_page(vma) ||
                        vma == get_gate_vma(current))) {
                downgrade_write(&mm->mmap_sem);
                nr_pages = __mlock_vma_pages_range(vma, start, end);

                up_read(&mm->mmap_sem);
                /* vma can change or disappear */
                down_write(&mm->mmap_sem);
                vma = find_vma(mm, start);
                /* non-NULL vma must contain @start, but need to check @end */
                if (!vma ||  end > vma->vm_end)
                        return -EAGAIN;
                return nr_pages;
        }

        /*
         * User mapped kernel pages or huge pages:
         * make these pages present to populate the ptes, but
         * fall thru' to reset VM_LOCKED--no need to unlock, and
         * return nr_pages so these don't get counted against task's
         * locked limit.  huge pages are already counted against
         * locked vm limit.
         */
        make_pages_present(start, end);

no_mlock:
        vma->vm_flags &= ~VM_LOCKED;    /* and don't come back! */
        return nr_pages;                /* pages NOT mlocked */
}


/*
 * munlock all pages in vma.   For munmap() and exit().
 */
void munlock_vma_pages_all(struct vm_area_struct *vma)
{
        vma->vm_flags &= ~VM_LOCKED;
        __munlock_vma_pages_range(vma, vma->vm_start, vma->vm_end);
}

/*
 * mlock_fixup  - handle mlock[all]/munlock[all] requests.
 *
 * Filters out "special" vmas -- VM_LOCKED never gets set for these, and
 * munlock is a no-op.  However, for some special vmas, we go ahead and
 * populate the ptes via make_pages_present().
 *
 * For vmas that pass the filters, merge/split as appropriate.
 */
static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
        unsigned long start, unsigned long end, unsigned int newflags)
{
        struct mm_struct *mm = vma->vm_mm;
        pgoff_t pgoff;
        int nr_pages;
        int ret = 0;
        int lock = newflags & VM_LOCKED;

        if (newflags == vma->vm_flags ||
                        (vma->vm_flags & (VM_IO | VM_PFNMAP)))
                goto out;       /* don't set VM_LOCKED,  don't count */

        if ((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
                        is_vm_hugetlb_page(vma) ||
                        vma == get_gate_vma(current)) {
                if (lock)
                        make_pages_present(start, end);
                goto out;       /* don't set VM_LOCKED,  don't count */
        }

        pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
        *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
                          vma->vm_file, pgoff, vma_policy(vma));
        if (*prev) {
                vma = *prev;
                goto success;
        }

        if (start != vma->vm_start) {
                ret = split_vma(mm, vma, start, 1);
                if (ret)
                        goto out;
        }

        if (end != vma->vm_end) {
                ret = split_vma(mm, vma, end, 0);
                if (ret)
                        goto out;
        }

success:
        /*
         * Keep track of amount of locked VM.
         */
        nr_pages = (end - start) >> PAGE_SHIFT;
        if (!lock)
                nr_pages = -nr_pages;
        mm->locked_vm += nr_pages;

        /*
         * vm_flags is protected by the mmap_sem held in write mode.
         * It's okay if try_to_unmap_one unmaps a page just after we
         * set VM_LOCKED, __mlock_vma_pages_range will bring it back.
         */
        vma->vm_flags = newflags;

        if (lock) {
                /*
                 * mmap_sem is currently held for write.  Downgrade the write
                 * lock to a read lock so that other faults, mmap scans, ...
                 * while we fault in all pages.
                 */
                downgrade_write(&mm->mmap_sem);

                ret = __mlock_vma_pages_range(vma, start, end);
                if (ret > 0) {
                        mm->locked_vm -= ret;
                        ret = 0;
                }
                /*
                 * Need to reacquire mmap sem in write mode, as our callers
                 * expect this.  We have no support for atomically upgrading
                 * a sem to write, so we need to check for ranges while sem
                 * is unlocked.
                 */
                up_read(&mm->mmap_sem);
                /* vma can change or disappear */
                down_write(&mm->mmap_sem);
                *prev = find_vma(mm, start);
                /* non-NULL *prev must contain @start, but need to check @end */
                if (!(*prev) || end > (*prev)->vm_end)
                        ret = -EAGAIN;
        } else {
                /*
                 * TODO:  for unlocking, pages will already be resident, so
                 * we don't need to wait for allocations/reclaim/pagein, ...
                 * However, unlocking a very large region can still take a
                 * while.  Should we downgrade the semaphore for both lock
                 * AND unlock ?
                 */
                __munlock_vma_pages_range(vma, start, end);
        }

out:
        *prev = vma;
        return ret;
}

static int do_mlock(unsigned long start, size_t len, int on)
{
        unsigned long nstart, end, tmp;
        struct vm_area_struct * vma, * prev;
        int error;

        len = PAGE_ALIGN(len);
        end = start + len;
        if (end < start)
                return -EINVAL;
        if (end == start)
                return 0;
        vma = find_vma_prev(current->mm, start, &prev);
        if (!vma || vma->vm_start > start)
                return -ENOMEM;

        if (start > vma->vm_start)
                prev = vma;

        for (nstart = start ; ; ) {
                unsigned int newflags;

                /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */

                newflags = vma->vm_flags | VM_LOCKED;
                if (!on)
                        newflags &= ~VM_LOCKED;

                tmp = vma->vm_end;
                if (tmp > end)
                        tmp = end;
                error = mlock_fixup(vma, &prev, nstart, tmp, newflags);
                if (error)
                        break;
                nstart = tmp;
                if (nstart < prev->vm_end)
                        nstart = prev->vm_end;
                if (nstart >= end)
                        break;

                vma = prev->vm_next;
                if (!vma || vma->vm_start != nstart) {
                        error = -ENOMEM;
                        break;
                }
        }
        return error;
}

asmlinkage long sys_mlock(unsigned long start, size_t len)
{
        unsigned long locked;
        unsigned long lock_limit;
        int error = -ENOMEM;

        if (!can_do_mlock())
                return -EPERM;

        down_write(&current->mm->mmap_sem);
        len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
        start &= PAGE_MASK;

        locked = len >> PAGE_SHIFT;
        locked += current->mm->locked_vm;

        lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
        lock_limit >>= PAGE_SHIFT;

        /* check against resource limits */
        if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
                error = do_mlock(start, len, 1);
        up_write(&current->mm->mmap_sem);
        return error;
}

asmlinkage long sys_munlock(unsigned long start, size_t len)
{
        int ret;

        down_write(&current->mm->mmap_sem);
        len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
        start &= PAGE_MASK;
        ret = do_mlock(start, len, 0);
        up_write(&current->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;
}

asmlinkage long sys_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;

        down_write(&current->mm->mmap_sem);

        lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
        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(&current->mm->mmap_sem);
out:
        return ret;
}

asmlinkage long sys_munlockall(void)
{
        int ret;

        down_write(&current->mm->mmap_sem);
        ret = do_mlockall(0);
        up_write(&current->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 = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
        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);
}