drivers/spi: move a dereference below a NULL test

[linux-2.6/mini2440.git] / kernel / acct.c

/*
 *  linux/kernel/acct.c
 *
 *  BSD Process Accounting for Linux
 *
 *  Author: Marco van Wieringen <mvw@planets.elm.net>
 *
 *  Some code based on ideas and code from:
 *  Thomas K. Dyas <tdyas@eden.rutgers.edu>
 *
 *  This file implements BSD-style process accounting. Whenever any
 *  process exits, an accounting record of type "struct acct" is
 *  written to the file specified with the acct() system call. It is
 *  up to user-level programs to do useful things with the accounting
 *  log. The kernel just provides the raw accounting information.
 *
 * (C) Copyright 1995 - 1997 Marco van Wieringen - ELM Consultancy B.V.
 *
 *  Plugged two leaks. 1) It didn't return acct_file into the free_filps if
 *  the file happened to be read-only. 2) If the accounting was suspended
 *  due to the lack of space it happily allowed to reopen it and completely
 *  lost the old acct_file. 3/10/98, Al Viro.
 *
 *  Now we silently close acct_file on attempt to reopen. Cleaned sys_acct().
 *  XTerms and EMACS are manifestations of pure evil. 21/10/98, AV.
 *
 *  Fixed a nasty interaction with with sys_umount(). If the accointing
 *  was suspeneded we failed to stop it on umount(). Messy.
 *  Another one: remount to readonly didn't stop accounting.
 *      Question: what should we do if we have CAP_SYS_ADMIN but not
 *  CAP_SYS_PACCT? Current code does the following: umount returns -EBUSY
 *  unless we are messing with the root. In that case we are getting a
 *  real mess with do_remount_sb(). 9/11/98, AV.
 *
 *  Fixed a bunch of races (and pair of leaks). Probably not the best way,
 *  but this one obviously doesn't introduce deadlocks. Later. BTW, found
 *  one race (and leak) in BSD implementation.
 *  OK, that's better. ANOTHER race and leak in BSD variant. There always
 *  is one more bug... 10/11/98, AV.
 *
 *      Oh, fsck... Oopsable SMP race in do_process_acct() - we must hold
 * ->mmap_sem to walk the vma list of current->mm. Nasty, since it leaks
 * a struct file opened for write. Fixed. 2/6/2000, AV.
 */

#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/acct.h>
#include <linux/capability.h>
#include <linux/file.h>
#include <linux/tty.h>
#include <linux/security.h>
#include <linux/vfs.h>
#include <linux/jiffies.h>
#include <linux/times.h>
#include <linux/syscalls.h>
#include <linux/mount.h>
#include <asm/uaccess.h>
#include <asm/div64.h>
#include <linux/blkdev.h> /* sector_div */
#include <linux/pid_namespace.h>

/*
 * These constants control the amount of freespace that suspend and
 * resume the process accounting system, and the time delay between
 * each check.
 * Turned into sysctl-controllable parameters. AV, 12/11/98
 */

int acct_parm[3] = {4, 2, 30};
#define RESUME          (acct_parm[0])  /* >foo% free space - resume */
#define SUSPEND         (acct_parm[1])  /* <foo% free space - suspend */
#define ACCT_TIMEOUT    (acct_parm[2])  /* foo second timeout between checks */

/*
 * External references and all of the globals.
 */
static void do_acct_process(struct bsd_acct_struct *acct,
                struct pid_namespace *ns, struct file *);

/*
 * This structure is used so that all the data protected by lock
 * can be placed in the same cache line as the lock.  This primes
 * the cache line to have the data after getting the lock.
 */
struct bsd_acct_struct {
        volatile int            active;
        volatile int            needcheck;
        struct file             *file;
        struct pid_namespace    *ns;
        struct timer_list       timer;
        struct list_head        list;
};

static DEFINE_SPINLOCK(acct_lock);
static LIST_HEAD(acct_list);

/*
 * Called whenever the timer says to check the free space.
 */
static void acct_timeout(unsigned long x)
{
        struct bsd_acct_struct *acct = (struct bsd_acct_struct *)x;
        acct->needcheck = 1;
}

/*
 * Check the amount of free space and suspend/resume accordingly.
 */
static int check_free_space(struct bsd_acct_struct *acct, struct file *file)
{
        struct kstatfs sbuf;
        int res;
        int act;
        sector_t resume;
        sector_t suspend;

        spin_lock(&acct_lock);
        res = acct->active;
        if (!file || !acct->needcheck)
                goto out;
        spin_unlock(&acct_lock);

        /* May block */
        if (vfs_statfs(file->f_path.dentry, &sbuf))
                return res;
        suspend = sbuf.f_blocks * SUSPEND;
        resume = sbuf.f_blocks * RESUME;

        sector_div(suspend, 100);
        sector_div(resume, 100);

        if (sbuf.f_bavail <= suspend)
                act = -1;
        else if (sbuf.f_bavail >= resume)
                act = 1;
        else
                act = 0;

        /*
         * If some joker switched acct->file under us we'ld better be
         * silent and _not_ touch anything.
         */
        spin_lock(&acct_lock);
        if (file != acct->file) {
                if (act)
                        res = act>0;
                goto out;
        }

        if (acct->active) {
                if (act < 0) {
                        acct->active = 0;
                        printk(KERN_INFO "Process accounting paused\n");
                }
        } else {
                if (act > 0) {
                        acct->active = 1;
                        printk(KERN_INFO "Process accounting resumed\n");
                }
        }

        del_timer(&acct->timer);
        acct->needcheck = 0;
        acct->timer.expires = jiffies + ACCT_TIMEOUT*HZ;
        add_timer(&acct->timer);
        res = acct->active;
out:
        spin_unlock(&acct_lock);
        return res;
}

/*
 * Close the old accounting file (if currently open) and then replace
 * it with file (if non-NULL).
 *
 * NOTE: acct_lock MUST be held on entry and exit.
 */
static void acct_file_reopen(struct bsd_acct_struct *acct, struct file *file,
                struct pid_namespace *ns)
{
        struct file *old_acct = NULL;
        struct pid_namespace *old_ns = NULL;

        if (acct->file) {
                old_acct = acct->file;
                old_ns = acct->ns;
                del_timer(&acct->timer);
                acct->active = 0;
                acct->needcheck = 0;
                acct->file = NULL;
                acct->ns = NULL;
                list_del(&acct->list);
        }
        if (file) {
                acct->file = file;
                acct->ns = ns;
                acct->needcheck = 0;
                acct->active = 1;
                list_add(&acct->list, &acct_list);
                /* It's been deleted if it was used before so this is safe */
                setup_timer(&acct->timer, acct_timeout, (unsigned long)acct);
                acct->timer.expires = jiffies + ACCT_TIMEOUT*HZ;
                add_timer(&acct->timer);
        }
        if (old_acct) {
                mnt_unpin(old_acct->f_path.mnt);
                spin_unlock(&acct_lock);
                do_acct_process(acct, old_ns, old_acct);
                filp_close(old_acct, NULL);
                spin_lock(&acct_lock);
        }
}

static int acct_on(char *name)
{
        struct file *file;
        int error;
        struct pid_namespace *ns;
        struct bsd_acct_struct *acct = NULL;

        /* Difference from BSD - they don't do O_APPEND */
        file = filp_open(name, O_WRONLY|O_APPEND|O_LARGEFILE, 0);
        if (IS_ERR(file))
                return PTR_ERR(file);

        if (!S_ISREG(file->f_path.dentry->d_inode->i_mode)) {
                filp_close(file, NULL);
                return -EACCES;
        }

        if (!file->f_op->write) {
                filp_close(file, NULL);
                return -EIO;
        }

        ns = task_active_pid_ns(current);
        if (ns->bacct == NULL) {
                acct = kzalloc(sizeof(struct bsd_acct_struct), GFP_KERNEL);
                if (acct == NULL) {
                        filp_close(file, NULL);
                        return -ENOMEM;
                }
        }

        error = security_acct(file);
        if (error) {
                kfree(acct);
                filp_close(file, NULL);
                return error;
        }

        spin_lock(&acct_lock);
        if (ns->bacct == NULL) {
                ns->bacct = acct;
                acct = NULL;
        }

        mnt_pin(file->f_path.mnt);
        acct_file_reopen(ns->bacct, file, ns);
        spin_unlock(&acct_lock);

        mntput(file->f_path.mnt); /* it's pinned, now give up active reference */
        kfree(acct);

        return 0;
}

/**
 * sys_acct - enable/disable process accounting
 * @name: file name for accounting records or NULL to shutdown accounting
 *
 * Returns 0 for success or negative errno values for failure.
 *
 * sys_acct() is the only system call needed to implement process
 * accounting. It takes the name of the file where accounting records
 * should be written. If the filename is NULL, accounting will be
 * shutdown.
 */
asmlinkage long sys_acct(const char __user *name)
{
        int error;

        if (!capable(CAP_SYS_PACCT))
                return -EPERM;

        if (name) {
                char *tmp = getname(name);
                if (IS_ERR(tmp))
                        return (PTR_ERR(tmp));
                error = acct_on(tmp);
                putname(tmp);
        } else {
                struct bsd_acct_struct *acct;

                acct = task_active_pid_ns(current)->bacct;
                if (acct == NULL)
                        return 0;

                error = security_acct(NULL);
                if (!error) {
                        spin_lock(&acct_lock);
                        acct_file_reopen(acct, NULL, NULL);
                        spin_unlock(&acct_lock);
                }
        }
        return error;
}

/**
 * acct_auto_close - turn off a filesystem's accounting if it is on
 * @m: vfsmount being shut down
 *
 * If the accounting is turned on for a file in the subtree pointed to
 * to by m, turn accounting off.  Done when m is about to die.
 */
void acct_auto_close_mnt(struct vfsmount *m)
{
        struct bsd_acct_struct *acct;

        spin_lock(&acct_lock);
restart:
        list_for_each_entry(acct, &acct_list, list)
                if (acct->file && acct->file->f_path.mnt == m) {
                        acct_file_reopen(acct, NULL, NULL);
                        goto restart;
                }
        spin_unlock(&acct_lock);
}

/**
 * acct_auto_close - turn off a filesystem's accounting if it is on
 * @sb: super block for the filesystem
 *
 * If the accounting is turned on for a file in the filesystem pointed
 * to by sb, turn accounting off.
 */
void acct_auto_close(struct super_block *sb)
{
        struct bsd_acct_struct *acct;

        spin_lock(&acct_lock);
restart:
        list_for_each_entry(acct, &acct_list, list)
                if (acct->file && acct->file->f_path.mnt->mnt_sb == sb) {
                        acct_file_reopen(acct, NULL, NULL);
                        goto restart;
                }
        spin_unlock(&acct_lock);
}

void acct_exit_ns(struct pid_namespace *ns)
{
        struct bsd_acct_struct *acct;

        spin_lock(&acct_lock);
        acct = ns->bacct;
        if (acct != NULL) {
                if (acct->file != NULL)
                        acct_file_reopen(acct, NULL, NULL);

                kfree(acct);
        }
        spin_unlock(&acct_lock);
}

/*
 *  encode an unsigned long into a comp_t
 *
 *  This routine has been adopted from the encode_comp_t() function in
 *  the kern_acct.c file of the FreeBSD operating system. The encoding
 *  is a 13-bit fraction with a 3-bit (base 8) exponent.
 */

#define MANTSIZE        13                      /* 13 bit mantissa. */
#define EXPSIZE         3                       /* Base 8 (3 bit) exponent. */
#define MAXFRACT        ((1 << MANTSIZE) - 1)   /* Maximum fractional value. */

static comp_t encode_comp_t(unsigned long value)
{
        int exp, rnd;

        exp = rnd = 0;
        while (value > MAXFRACT) {
                rnd = value & (1 << (EXPSIZE - 1));     /* Round up? */
                value >>= EXPSIZE;      /* Base 8 exponent == 3 bit shift. */
                exp++;
        }

        /*
         * If we need to round up, do it (and handle overflow correctly).
         */
        if (rnd && (++value > MAXFRACT)) {
                value >>= EXPSIZE;
                exp++;
        }

        /*
         * Clean it up and polish it off.
         */
        exp <<= MANTSIZE;               /* Shift the exponent into place */
        exp += value;                   /* and add on the mantissa. */
        return exp;
}

#if ACCT_VERSION==1 || ACCT_VERSION==2
/*
 * encode an u64 into a comp2_t (24 bits)
 *
 * Format: 5 bit base 2 exponent, 20 bits mantissa.
 * The leading bit of the mantissa is not stored, but implied for
 * non-zero exponents.
 * Largest encodable value is 50 bits.
 */

#define MANTSIZE2       20                      /* 20 bit mantissa. */
#define EXPSIZE2        5                       /* 5 bit base 2 exponent. */
#define MAXFRACT2       ((1ul << MANTSIZE2) - 1) /* Maximum fractional value. */
#define MAXEXP2         ((1 <<EXPSIZE2) - 1)    /* Maximum exponent. */

static comp2_t encode_comp2_t(u64 value)
{
        int exp, rnd;

        exp = (value > (MAXFRACT2>>1));
        rnd = 0;
        while (value > MAXFRACT2) {
                rnd = value & 1;
                value >>= 1;
                exp++;
        }

        /*
         * If we need to round up, do it (and handle overflow correctly).
         */
        if (rnd && (++value > MAXFRACT2)) {
                value >>= 1;
                exp++;
        }

        if (exp > MAXEXP2) {
                /* Overflow. Return largest representable number instead. */
                return (1ul << (MANTSIZE2+EXPSIZE2-1)) - 1;
        } else {
                return (value & (MAXFRACT2>>1)) | (exp << (MANTSIZE2-1));
        }
}
#endif

#if ACCT_VERSION==3
/*
 * encode an u64 into a 32 bit IEEE float
 */
static u32 encode_float(u64 value)
{
        unsigned exp = 190;
        unsigned u;

        if (value==0) return 0;
        while ((s64)value > 0){
                value <<= 1;
                exp--;
        }
        u = (u32)(value >> 40) & 0x7fffffu;
        return u | (exp << 23);
}
#endif

/*
 *  Write an accounting entry for an exiting process
 *
 *  The acct_process() call is the workhorse of the process
 *  accounting system. The struct acct is built here and then written
 *  into the accounting file. This function should only be called from
 *  do_exit() or when switching to a different output file.
 */

/*
 *  do_acct_process does all actual work. Caller holds the reference to file.
 */
static void do_acct_process(struct bsd_acct_struct *acct,
                struct pid_namespace *ns, struct file *file)
{
        struct pacct_struct *pacct = &current->signal->pacct;
        acct_t ac;
        mm_segment_t fs;
        unsigned long flim;
        u64 elapsed;
        u64 run_time;
        struct timespec uptime;
        struct tty_struct *tty;

        /*
         * First check to see if there is enough free_space to continue
         * the process accounting system.
         */
        if (!check_free_space(acct, file))
                return;

        /*
         * Fill the accounting struct with the needed info as recorded
         * by the different kernel functions.
         */
        memset((caddr_t)&ac, 0, sizeof(acct_t));

        ac.ac_version = ACCT_VERSION | ACCT_BYTEORDER;
        strlcpy(ac.ac_comm, current->comm, sizeof(ac.ac_comm));

        /* calculate run_time in nsec*/
        do_posix_clock_monotonic_gettime(&uptime);
        run_time = (u64)uptime.tv_sec*NSEC_PER_SEC + uptime.tv_nsec;
        run_time -= (u64)current->group_leader->start_time.tv_sec * NSEC_PER_SEC
                       + current->group_leader->start_time.tv_nsec;
        /* convert nsec -> AHZ */
        elapsed = nsec_to_AHZ(run_time);
#if ACCT_VERSION==3
        ac.ac_etime = encode_float(elapsed);
#else
        ac.ac_etime = encode_comp_t(elapsed < (unsigned long) -1l ?
                               (unsigned long) elapsed : (unsigned long) -1l);
#endif
#if ACCT_VERSION==1 || ACCT_VERSION==2
        {
                /* new enlarged etime field */
                comp2_t etime = encode_comp2_t(elapsed);
                ac.ac_etime_hi = etime >> 16;
                ac.ac_etime_lo = (u16) etime;
        }
#endif
        do_div(elapsed, AHZ);
        ac.ac_btime = get_seconds() - elapsed;
        /* we really need to bite the bullet and change layout */
        current_uid_gid(&ac.ac_uid, &ac.ac_gid);
#if ACCT_VERSION==2
        ac.ac_ahz = AHZ;
#endif
#if ACCT_VERSION==1 || ACCT_VERSION==2
        /* backward-compatible 16 bit fields */
        ac.ac_uid16 = ac.ac_uid;
        ac.ac_gid16 = ac.ac_gid;
#endif
#if ACCT_VERSION==3
        ac.ac_pid = task_tgid_nr_ns(current, ns);
        rcu_read_lock();
        ac.ac_ppid = task_tgid_nr_ns(rcu_dereference(current->real_parent), ns);
        rcu_read_unlock();
#endif

        spin_lock_irq(&current->sighand->siglock);
        tty = current->signal->tty;     /* Safe as we hold the siglock */
        ac.ac_tty = tty ? old_encode_dev(tty_devnum(tty)) : 0;
        ac.ac_utime = encode_comp_t(jiffies_to_AHZ(cputime_to_jiffies(pacct->ac_utime)));
        ac.ac_stime = encode_comp_t(jiffies_to_AHZ(cputime_to_jiffies(pacct->ac_stime)));
        ac.ac_flag = pacct->ac_flag;
        ac.ac_mem = encode_comp_t(pacct->ac_mem);
        ac.ac_minflt = encode_comp_t(pacct->ac_minflt);
        ac.ac_majflt = encode_comp_t(pacct->ac_majflt);
        ac.ac_exitcode = pacct->ac_exitcode;
        spin_unlock_irq(&current->sighand->siglock);
        ac.ac_io = encode_comp_t(0 /* current->io_usage */);    /* %% */
        ac.ac_rw = encode_comp_t(ac.ac_io / 1024);
        ac.ac_swaps = encode_comp_t(0);

        /*
         * Kernel segment override to datasegment and write it
         * to the accounting file.
         */
        fs = get_fs();
        set_fs(KERNEL_DS);
        /*
         * Accounting records are not subject to resource limits.
         */
        flim = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
        current->signal->rlim[RLIMIT_FSIZE].rlim_cur = RLIM_INFINITY;
        file->f_op->write(file, (char *)&ac,
                               sizeof(acct_t), &file->f_pos);
        current->signal->rlim[RLIMIT_FSIZE].rlim_cur = flim;
        set_fs(fs);
}

/**
 * acct_init_pacct - initialize a new pacct_struct
 * @pacct: per-process accounting info struct to initialize
 */
void acct_init_pacct(struct pacct_struct *pacct)
{
        memset(pacct, 0, sizeof(struct pacct_struct));
        pacct->ac_utime = pacct->ac_stime = cputime_zero;
}

/**
 * acct_collect - collect accounting information into pacct_struct
 * @exitcode: task exit code
 * @group_dead: not 0, if this thread is the last one in the process.
 */
void acct_collect(long exitcode, int group_dead)
{
        struct pacct_struct *pacct = &current->signal->pacct;
        unsigned long vsize = 0;

        if (group_dead && current->mm) {
                struct vm_area_struct *vma;
                down_read(&current->mm->mmap_sem);
                vma = current->mm->mmap;
                while (vma) {
                        vsize += vma->vm_end - vma->vm_start;
                        vma = vma->vm_next;
                }
                up_read(&current->mm->mmap_sem);
        }

        spin_lock_irq(&current->sighand->siglock);
        if (group_dead)
                pacct->ac_mem = vsize / 1024;
        if (thread_group_leader(current)) {
                pacct->ac_exitcode = exitcode;
                if (current->flags & PF_FORKNOEXEC)
                        pacct->ac_flag |= AFORK;
        }
        if (current->flags & PF_SUPERPRIV)
                pacct->ac_flag |= ASU;
        if (current->flags & PF_DUMPCORE)
                pacct->ac_flag |= ACORE;
        if (current->flags & PF_SIGNALED)
                pacct->ac_flag |= AXSIG;
        pacct->ac_utime = cputime_add(pacct->ac_utime, current->utime);
        pacct->ac_stime = cputime_add(pacct->ac_stime, current->stime);
        pacct->ac_minflt += current->min_flt;
        pacct->ac_majflt += current->maj_flt;
        spin_unlock_irq(&current->sighand->siglock);
}

static void acct_process_in_ns(struct pid_namespace *ns)
{
        struct file *file = NULL;
        struct bsd_acct_struct *acct;

        acct = ns->bacct;
        /*
         * accelerate the common fastpath:
         */
        if (!acct || !acct->file)
                return;

        spin_lock(&acct_lock);
        file = acct->file;
        if (unlikely(!file)) {
                spin_unlock(&acct_lock);
                return;
        }
        get_file(file);
        spin_unlock(&acct_lock);

        do_acct_process(acct, ns, file);
        fput(file);
}

/**
 * acct_process - now just a wrapper around acct_process_in_ns,
 * which in turn is a wrapper around do_acct_process.
 *
 * handles process accounting for an exiting task
 */
void acct_process(void)
{
        struct pid_namespace *ns;

        /*
         * This loop is safe lockless, since current is still
         * alive and holds its namespace, which in turn holds
         * its parent.
         */
        for (ns = task_active_pid_ns(current); ns != NULL; ns = ns->parent)
                acct_process_in_ns(ns);
}