Import 2.3.12pre9

[davej-history.git] / kernel / fork.c

/*
 *  linux/kernel/fork.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

/*
 *  'fork.c' contains the help-routines for the 'fork' system call
 * (see also system_call.s).
 * Fork is rather simple, once you get the hang of it, but the memory
 * management can be a bitch. See 'mm/mm.c': 'copy_page_tables()'
 */

#include <linux/malloc.h>
#include <linux/init.h>
#include <linux/unistd.h>
#include <linux/smp_lock.h>
#include <linux/module.h>
#include <linux/vmalloc.h>

#include <asm/pgtable.h>
#include <asm/mmu_context.h>
#include <asm/uaccess.h>

/* The idle threads do not count.. */
int nr_threads=0;
int nr_running=0;

int max_threads;
unsigned long total_forks = 0;  /* Handle normal Linux uptimes. */
int last_pid=0;

/* SLAB cache for mm_struct's. */
kmem_cache_t *mm_cachep;

/* SLAB cache for files structs */
kmem_cache_t *files_cachep; 

struct task_struct *pidhash[PIDHASH_SZ];

/* UID task count cache, to prevent walking entire process list every
 * single fork() operation.
 */
#define UIDHASH_SZ      (PIDHASH_SZ >> 2)

static struct user_struct {
        atomic_t count;
        struct user_struct *next, **pprev;
        unsigned int uid;
} *uidhash[UIDHASH_SZ];

spinlock_t uidhash_lock = SPIN_LOCK_UNLOCKED;

kmem_cache_t *uid_cachep;

#define uidhashfn(uid)  (((uid >> 8) ^ uid) & (UIDHASH_SZ - 1))

/*
 * These routines must be called with the uidhash spinlock held!
 */
static inline void uid_hash_insert(struct user_struct *up, unsigned int hashent)
{
        if((up->next = uidhash[hashent]) != NULL)
                uidhash[hashent]->pprev = &up->next;
        up->pprev = &uidhash[hashent];
        uidhash[hashent] = up;
}

static inline void uid_hash_remove(struct user_struct *up)
{
        if(up->next)
                up->next->pprev = up->pprev;
        *up->pprev = up->next;
}

static inline struct user_struct *uid_hash_find(unsigned short uid, unsigned int hashent)
{
        struct user_struct *up, *next;

        next = uidhash[hashent];
        for (;;) {
                up = next;
                if (next) {
                        next = up->next;
                        if (up->uid != uid)
                                continue;
                        atomic_inc(&up->count);
                }
                break;
        }
        return up;
}

/*
 * For SMP, we need to re-test the user struct counter
 * after having aquired the spinlock. This allows us to do
 * the common case (not freeing anything) without having
 * any locking.
 */
#ifdef __SMP__
  #define uid_hash_free(up)     (!atomic_read(&(up)->count))
#else
  #define uid_hash_free(up)     (1)
#endif

void free_uid(struct task_struct *p)
{
        struct user_struct *up = p->user;

        if (up) {
                p->user = NULL;
                if (atomic_dec_and_test(&up->count)) {
                        spin_lock(&uidhash_lock);
                        if (uid_hash_free(up)) {
                                uid_hash_remove(up);
                                kmem_cache_free(uid_cachep, up);
                        }
                        spin_unlock(&uidhash_lock);
                }
        }
}

int alloc_uid(struct task_struct *p)
{
        unsigned int hashent = uidhashfn(p->uid);
        struct user_struct *up;

        spin_lock(&uidhash_lock);
        up = uid_hash_find(p->uid, hashent);
        spin_unlock(&uidhash_lock);

        if (!up) {
                struct user_struct *new;

                new = kmem_cache_alloc(uid_cachep, SLAB_KERNEL);
                if (!new)
                        return -EAGAIN;
                new->uid = p->uid;
                atomic_set(&new->count, 1);

                /*
                 * Before adding this, check whether we raced
                 * on adding the same user already..
                 */
                spin_lock(&uidhash_lock);
                up = uid_hash_find(p->uid, hashent);
                if (up) {
                        kmem_cache_free(uid_cachep, new);
                } else {
                        uid_hash_insert(new, hashent);
                        up = new;
                }
                spin_unlock(&uidhash_lock);

        }
        p->user = up;
        return 0;
}

void __init fork_init(unsigned long memsize)
{
        int i;

        uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
                                       0,
                                       SLAB_HWCACHE_ALIGN, NULL, NULL);
        if(!uid_cachep)
                panic("Cannot create uid taskcount SLAB cache\n");

        for(i = 0; i < UIDHASH_SZ; i++)
                uidhash[i] = 0;

        /*
         * The default maximum number of threads is set to a safe
         * value: the thread structures can take up at most half
         * of memory.
         */
        max_threads = memsize / THREAD_SIZE / 2;

        init_task.rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
        init_task.rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
}

/* Protects next_safe and last_pid. */
spinlock_t lastpid_lock = SPIN_LOCK_UNLOCKED;

static int get_pid(unsigned long flags)
{
        static int next_safe = PID_MAX;
        struct task_struct *p;

        if (flags & CLONE_PID)
                return current->pid;

        spin_lock(&lastpid_lock);
        if((++last_pid) & 0xffff8000) {
                last_pid = 300;         /* Skip daemons etc. */
                goto inside;
        }
        if(last_pid >= next_safe) {
inside:
                next_safe = PID_MAX;
                read_lock(&tasklist_lock);
        repeat:
                for_each_task(p) {
                        if(p->pid == last_pid   ||
                           p->pgrp == last_pid  ||
                           p->session == last_pid) {
                                if(++last_pid >= next_safe) {
                                        if(last_pid & 0xffff8000)
                                                last_pid = 300;
                                        next_safe = PID_MAX;
                                }
                                goto repeat;
                        }
                        if(p->pid > last_pid && next_safe > p->pid)
                                next_safe = p->pid;
                        if(p->pgrp > last_pid && next_safe > p->pgrp)
                                next_safe = p->pgrp;
                        if(p->session > last_pid && next_safe > p->session)
                                next_safe = p->session;
                }
                read_unlock(&tasklist_lock);
        }
        spin_unlock(&lastpid_lock);

        return last_pid;
}

static inline int dup_mmap(struct mm_struct * mm)
{
        struct vm_area_struct * mpnt, *tmp, **pprev;
        int retval;

        /* Kill me slowly. UGLY! FIXME! */
        memcpy(&mm->start_code, &current->mm->start_code, 15*sizeof(unsigned long));

        flush_cache_mm(current->mm);
        pprev = &mm->mmap;
        for (mpnt = current->mm->mmap ; mpnt ; mpnt = mpnt->vm_next) {
                struct file *file;

                retval = -ENOMEM;
                tmp = kmem_cache_alloc(vm_area_cachep, SLAB_KERNEL);
                if (!tmp)
                        goto fail_nomem;
                *tmp = *mpnt;
                tmp->vm_flags &= ~VM_LOCKED;
                tmp->vm_mm = mm;
                mm->map_count++;
                tmp->vm_next = NULL;
                file = tmp->vm_file;
                if (file) {
                        get_file(file);
                        if (tmp->vm_flags & VM_DENYWRITE)
                                atomic_dec(&file->f_dentry->d_inode->i_writecount);
      
                        /* insert tmp into the share list, just after mpnt */
                        spin_lock(&file->f_dentry->d_inode->i_shared_lock);
                        if((tmp->vm_next_share = mpnt->vm_next_share) != NULL)
                                mpnt->vm_next_share->vm_pprev_share =
                                        &tmp->vm_next_share;
                        mpnt->vm_next_share = tmp;
                        tmp->vm_pprev_share = &mpnt->vm_next_share;
                        spin_unlock(&file->f_dentry->d_inode->i_shared_lock);
                }

                /* Copy the pages, but defer checking for errors */
                retval = copy_page_range(mm, current->mm, tmp);
                if (!retval && tmp->vm_ops && tmp->vm_ops->open)
                        tmp->vm_ops->open(tmp);

                /*
                 * Link in the new vma even if an error occurred,
                 * so that exit_mmap() can clean up the mess.
                 */
                tmp->vm_next = *pprev;
                *pprev = tmp;

                pprev = &tmp->vm_next;
                if (retval)
                        goto fail_nomem;
        }
        retval = 0;
        if (mm->map_count >= AVL_MIN_MAP_COUNT)
                build_mmap_avl(mm);

fail_nomem:
        flush_tlb_mm(current->mm);
        return retval;
}

/*
 * Allocate and initialize an mm_struct.
 */
struct mm_struct * mm_alloc(void)
{
        struct mm_struct * mm;

        mm = kmem_cache_alloc(mm_cachep, SLAB_KERNEL);
        if (mm) {
                memset(mm, 0, sizeof(*mm));
                atomic_set(&mm->mm_users, 1);
                atomic_set(&mm->mm_count, 1);
                init_MUTEX(&mm->mmap_sem);
                mm->page_table_lock = SPIN_LOCK_UNLOCKED;
                mm->pgd = pgd_alloc();
                if (mm->pgd)
                        return mm;
                kmem_cache_free(mm_cachep, mm);
        }
        return NULL;
}

/*
 * Called when the last reference to the mm
 * is dropped: either by a lazy thread or by
 * mmput. Free the page directory and the mm.
 */
inline void __mmdrop(struct mm_struct *mm)
{
        if (mm == &init_mm) BUG();
        pgd_free(mm->pgd);
        kmem_cache_free(mm_cachep, mm);
}

/*
 * Decrement the use count and release all resources for an mm.
 */
void mmput(struct mm_struct *mm)
{
        if (atomic_dec_and_test(&mm->mm_users)) {
                exit_mmap(mm);
                mmdrop(mm);
        }
}

/* Please note the differences between mmput and mm_release.
 * mmput is called whenever we stop holding onto a mm_struct,
 * error success whatever.
 *
 * mm_release is called after a mm_struct has been removed
 * from the current process.
 *
 * This difference is important for error handling, when we
 * only half set up a mm_struct for a new process and need to restore
 * the old one.  Because we mmput the new mm_struct before
 * restoring the old one. . .
 * Eric Biederman 10 January 1998
 */
void mm_release(void)
{
        struct task_struct *tsk = current;
        forget_segments();
        /* notify parent sleeping on vfork() */
        if (tsk->flags & PF_VFORK) {
                tsk->flags &= ~PF_VFORK;
                up(tsk->p_opptr->vfork_sem);
        }
}

static inline int copy_mm(unsigned long clone_flags, struct task_struct * tsk)
{
        struct mm_struct * mm;
        int retval;

        tsk->min_flt = tsk->maj_flt = 0;
        tsk->cmin_flt = tsk->cmaj_flt = 0;
        tsk->nswap = tsk->cnswap = 0;

        tsk->mm = NULL;
        tsk->active_mm = NULL;

        /*
         * Are we cloning a kernel thread?
         *
         * We need to steal a active VM for that..
         */
        mm = current->mm;
        if (!mm)
                return 0;

        if (clone_flags & CLONE_VM) {
                atomic_inc(&mm->mm_users);
                goto good_mm;
        }

        retval = -ENOMEM;
        mm = mm_alloc();
        if (!mm)
                goto fail_nomem;

        tsk->mm = mm;
        tsk->active_mm = mm;

        /*
         * child gets a private LDT (if there was an LDT in the parent)
         */
        copy_segments(tsk, mm);

        down(&current->mm->mmap_sem);
        retval = dup_mmap(mm);
        up(&current->mm->mmap_sem);
        if (retval)
                goto free_pt;

good_mm:
        tsk->mm = mm;
        tsk->active_mm = mm;
        init_new_context(tsk,mm);
        return 0;

free_pt:
        mmput(mm);
fail_nomem:
        return retval;
}

static inline int copy_fs(unsigned long clone_flags, struct task_struct * tsk)
{
        if (clone_flags & CLONE_FS) {
                atomic_inc(&current->fs->count);
                return 0;
        }
        tsk->fs = kmalloc(sizeof(*tsk->fs), GFP_KERNEL);
        if (!tsk->fs)
                return -1;
        atomic_set(&tsk->fs->count, 1);
        tsk->fs->umask = current->fs->umask;
        tsk->fs->root = dget(current->fs->root);
        tsk->fs->pwd = dget(current->fs->pwd);
        return 0;
}

static int count_open_files(struct files_struct *files, int size)
{
        int i;
        
        /* Find the last open fd */
        for (i = size/(8*sizeof(long)); i > 0; ) {
                if (files->open_fds->fds_bits[--i])
                        break;
        }
        i = (i+1) * 8 * sizeof(long);
        return i;
}

static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
{
        struct files_struct *oldf, *newf;
        struct file **old_fds, **new_fds;
        int open_files, nfds, size, i, error = 0;

        /*
         * A background process may not have any files ...
         */
        oldf = current->files;
        if (!oldf)
                goto out;

        if (clone_flags & CLONE_FILES) {
                atomic_inc(&oldf->count);
                goto out;
        }

        tsk->files = NULL;
        error = -ENOMEM;
        newf = kmem_cache_alloc(files_cachep, SLAB_KERNEL);
        if (!newf) 
                goto out;

        atomic_set(&newf->count, 1);

        newf->file_lock     = RW_LOCK_UNLOCKED;
        newf->next_fd       = 0;
        newf->max_fds       = NR_OPEN_DEFAULT;
        newf->max_fdset     = __FD_SETSIZE;
        newf->close_on_exec = &newf->close_on_exec_init;
        newf->open_fds      = &newf->open_fds_init;
        newf->fd            = &newf->fd_array[0];

        /* We don't yet have the oldf readlock, but even if the old
           fdset gets grown now, we'll only copy up to "size" fds */
        size = oldf->max_fdset;
        if (size > __FD_SETSIZE) {
                newf->max_fdset = 0;
                write_lock(&newf->file_lock);
                error = expand_fdset(newf, size);
                write_unlock(&newf->file_lock);
                if (error)
                        goto out_release;
        }
        read_lock(&oldf->file_lock);

        open_files = count_open_files(oldf, size);

        /*
         * Check whether we need to allocate a larger fd array.
         * Note: we're not a clone task, so the open count won't
         * change.
         */
        nfds = NR_OPEN_DEFAULT;
        if (open_files > nfds) {
                read_unlock(&oldf->file_lock);
                newf->max_fds = 0;
                write_lock(&newf->file_lock);
                error = expand_fd_array(newf, open_files);
                write_unlock(&newf->file_lock);
                if (error) 
                        goto out_release;
                nfds = newf->max_fds;
                read_lock(&oldf->file_lock);
        }

        old_fds = oldf->fd;
        new_fds = newf->fd;

        memcpy(newf->open_fds->fds_bits, oldf->open_fds->fds_bits, open_files/8);
        memcpy(newf->close_on_exec->fds_bits, oldf->close_on_exec->fds_bits, open_files/8);

        for (i = open_files; i != 0; i--) {
                struct file *f = *old_fds++;
                if (f)
                        get_file(f);
                *new_fds++ = f;
        }
        read_unlock(&oldf->file_lock);

        /* compute the remainder to be cleared */
        size = (newf->max_fds - open_files) * sizeof(struct file *);

        /* This is long word aligned thus could use a optimized version */ 
        memset(new_fds, 0, size); 

        if (newf->max_fdset > open_files) {
                int left = (newf->max_fdset-open_files)/8;
                int start = open_files / (8 * sizeof(unsigned long));
                
                memset(&newf->open_fds->fds_bits[start], 0, left);
                memset(&newf->close_on_exec->fds_bits[start], 0, left);
        }

        tsk->files = newf;
        error = 0;
out:
        return error;

out_release:
        free_fdset (newf->close_on_exec, newf->max_fdset);
        free_fdset (newf->open_fds, newf->max_fdset);
        kmem_cache_free(files_cachep, newf);
        goto out;
}

static inline int copy_sighand(unsigned long clone_flags, struct task_struct * tsk)
{
        if (clone_flags & CLONE_SIGHAND) {
                atomic_inc(&current->sig->count);
                return 0;
        }
        tsk->sig = kmalloc(sizeof(*tsk->sig), GFP_KERNEL);
        if (!tsk->sig)
                return -1;
        spin_lock_init(&tsk->sig->siglock);
        atomic_set(&tsk->sig->count, 1);
        memcpy(tsk->sig->action, current->sig->action, sizeof(tsk->sig->action));
        return 0;
}

static inline void copy_flags(unsigned long clone_flags, struct task_struct *p)
{
        unsigned long new_flags = p->flags;

        new_flags &= ~(PF_SUPERPRIV | PF_USEDFPU | PF_VFORK);
        new_flags |= PF_FORKNOEXEC;
        if (!(clone_flags & CLONE_PTRACE))
                new_flags &= ~(PF_PTRACED|PF_TRACESYS);
        if (clone_flags & CLONE_VFORK)
                new_flags |= PF_VFORK;
        p->flags = new_flags;
}

/*
 *  Ok, this is the main fork-routine. It copies the system process
 * information (task[nr]) and sets up the necessary registers. It
 * also copies the data segment in its entirety.
 */
int do_fork(unsigned long clone_flags, unsigned long usp, struct pt_regs *regs)
{
        int retval = -ENOMEM;
        struct task_struct *p;
        DECLARE_MUTEX_LOCKED(sem);

        current->vfork_sem = &sem;

        p = alloc_task_struct();
        if (!p)
                goto fork_out;

        *p = *current;

        lock_kernel();

        retval = -EAGAIN;
        if (p->user) {
                if (atomic_read(&p->user->count) >= p->rlim[RLIMIT_NPROC].rlim_cur)
                        goto bad_fork_free;
                atomic_inc(&p->user->count);
        }

        /*
         * Counter atomicity is protected by
         * the kernel lock
         */
        if (nr_threads >= max_threads)
                goto bad_fork_cleanup_count;

        if (p->exec_domain && p->exec_domain->module)
                __MOD_INC_USE_COUNT(p->exec_domain->module);
        if (p->binfmt && p->binfmt->module)
                __MOD_INC_USE_COUNT(p->binfmt->module);

        p->did_exec = 0;
        p->swappable = 0;
        p->state = TASK_UNINTERRUPTIBLE;

        copy_flags(clone_flags, p);
        p->pid = get_pid(clone_flags);

        /*
         * This is a "shadow run" state. The process
         * is marked runnable, but isn't actually on
         * any run queue yet.. (that happens at the
         * very end).
         */
        p->state = TASK_RUNNING;
        p->run_list.next = NULL;
        p->run_list.prev = NULL;

        p->p_pptr = p->p_opptr = current;
        p->p_cptr = NULL;
        init_waitqueue_head(&p->wait_chldexit);
        p->vfork_sem = NULL;

        p->sigpending = 0;
        sigemptyset(&p->signal);
        p->sigqueue = NULL;
        p->sigqueue_tail = &p->sigqueue;

        p->it_real_value = p->it_virt_value = p->it_prof_value = 0;
        p->it_real_incr = p->it_virt_incr = p->it_prof_incr = 0;
        init_timer(&p->real_timer);
        p->real_timer.data = (unsigned long) p;

        p->leader = 0;          /* session leadership doesn't inherit */
        p->tty_old_pgrp = 0;
        p->times.tms_utime = p->times.tms_stime = 0;
        p->times.tms_cutime = p->times.tms_cstime = 0;
#ifdef __SMP__
        {
                int i;
                p->has_cpu = 0;
                p->processor = current->processor;
                /* ?? should we just memset this ?? */
                for(i = 0; i < smp_num_cpus; i++)
                        p->per_cpu_utime[i] = p->per_cpu_stime[i] = 0;
                spin_lock_init(&p->sigmask_lock);
        }
#endif
        p->lock_depth = -1;             /* -1 = no lock */
        p->start_time = jiffies;

        retval = -ENOMEM;
        /* copy all the process information */
        if (copy_files(clone_flags, p))
                goto bad_fork_cleanup;
        if (copy_fs(clone_flags, p))
                goto bad_fork_cleanup_files;
        if (copy_sighand(clone_flags, p))
                goto bad_fork_cleanup_fs;
        if (copy_mm(clone_flags, p))
                goto bad_fork_cleanup_sighand;
        retval = copy_thread(0, clone_flags, usp, p, regs);
        if (retval)
                goto bad_fork_cleanup_sighand;
        p->semundo = NULL;

        /* ok, now we should be set up.. */
        p->swappable = 1;
        p->exit_signal = clone_flags & CSIGNAL;
        p->pdeath_signal = 0;

        /*
         * "share" dynamic priority between parent and child, thus the
         * total amount of dynamic priorities in the system doesnt change,
         * more scheduling fairness. This is only important in the first
         * timeslice, on the long run the scheduling behaviour is unchanged.
         */
        current->counter >>= 1;
        p->counter = current->counter;

        /*
         * Ok, add it to the run-queues and make it
         * visible to the rest of the system.
         *
         * Let it rip!
         */
        retval = p->pid;
        write_lock_irq(&tasklist_lock);
        SET_LINKS(p);
        hash_pid(p);
        write_unlock_irq(&tasklist_lock);

        nr_threads++;
        wake_up_process(p);             /* do this last */
        ++total_forks;

bad_fork:
        unlock_kernel();
fork_out:
        if ((clone_flags & CLONE_VFORK) && (retval > 0)) 
                down(&sem);
        return retval;

bad_fork_cleanup_sighand:
        exit_sighand(p);
bad_fork_cleanup_fs:
        exit_fs(p); /* blocking */
bad_fork_cleanup_files:
        exit_files(p); /* blocking */
bad_fork_cleanup:
        if (p->exec_domain && p->exec_domain->module)
                __MOD_DEC_USE_COUNT(p->exec_domain->module);
        if (p->binfmt && p->binfmt->module)
                __MOD_DEC_USE_COUNT(p->binfmt->module);

        nr_threads--;
bad_fork_cleanup_count:
        if (p->user)
                free_uid(p);
bad_fork_free:
        free_task_struct(p);
        goto bad_fork;
}

void __init filescache_init(void)
{
        files_cachep = kmem_cache_create("files_cache", 
                                         sizeof(struct files_struct),
                                         0, 
                                         SLAB_HWCACHE_ALIGN,
                                         NULL, NULL);
        if (!files_cachep) 
                panic("Cannot create files cache"); 
}