root/mm/mlock.c

DEFINITIONS

1. can_do_mlock
2. mlock_fixup
3. do_mlock
4. sys_mlock
5. sys_munlock
6. do_mlockall
7. sys_mlockall
8. sys_munlockall
9. user_shm_lock
10. user_shm_unlock

/*
 *      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/mempolicy.h>
#include <linux/syscalls.h>
#include <linux/sched.h>
#include <linux/module.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);

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 pages;
        int ret = 0;

        if (newflags == vma->vm_flags) {
                *prev = vma;
                goto out;
        }

        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;
        }

        *prev = vma;

        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:
        /*
         * 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, make_pages_present below will bring it back.
         */
        vma->vm_flags = newflags;

        /*
         * Keep track of amount of locked VM.
         */
        pages = (end - start) >> PAGE_SHIFT;
        if (newflags & VM_LOCKED) {
                pages = -pages;
                if (!(newflags & VM_IO))
                        ret = make_pages_present(start, end);
        }

        mm->locked_vm -= pages;
out:
        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);
}