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linux/kernel/acct.c
Al Viro 7b7b1ace2d [PATCH] saner handling of auto_acct_off() and DQUOT_OFF() in umount 
The way we currently deal with quota and process accounting that might
keep vfsmount busy at umount time is inherently broken; we try to turn
them off just in case (not quite correctly, at that) and

  a) pray umount doesn't fail (otherwise they'll stay turned off)
  b) pray nobody doesn anything funny just as we turn quota off

Moreover, LSM provides hooks for doing the same sort of broken logics.

The proper way to deal with that is to introduce the second kind of
reference to vfsmount.  Semantics:

 - when the last normal reference is dropped, all special ones are
   converted to normal ones and if there had been any, cleanup is done.
 - normal reference can be cloned into a special one
 - special reference can be converted to normal one; that's a no-op if
   we'd already passed the point of no return (i.e.  mntput() had
   converted special references to normal and started cleanup).

The way it works: e.g. starting process accounting converts the vfsmount
reference pinned by the opened file into special one and turns it back
to normal when it gets shut down; acct_auto_close() is done when no
normal references are left.  That way it does *not* obstruct umount(2)
and it silently gets turned off when the last normal reference to
vfsmount is gone.  Which is exactly what we want...

The same should be done by LSM module that holds some internal
references to vfsmount and wants to shut them down on umount - it should
make them special and security_sb_umount_close() will be called exactly
when the last normal reference to vfsmount is gone.

quota handling is even simpler - we don't use normal file IO anymore, so
there's no need to hold vfsmounts at all.  DQUOT_OFF() is done from
deactivate_super(), where it really belongs.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-11-07 18:18:09 -08:00

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/*
* 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/config.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/acct.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 */
/*
* 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(long, 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 acct_glbs {
spinlock_t lock;
volatile int active;
volatile int needcheck;
struct file *file;
struct timer_list timer;
};
static struct acct_glbs acct_globals __cacheline_aligned = {SPIN_LOCK_UNLOCKED};
/*
* Called whenever the timer says to check the free space.
*/
static void acct_timeout(unsigned long unused)
{
acct_globals.needcheck = 1;
}
/*
* Check the amount of free space and suspend/resume accordingly.
*/
static int check_free_space(struct file *file)
{
struct kstatfs sbuf;
int res;
int act;
sector_t resume;
sector_t suspend;
spin_lock(&acct_globals.lock);
res = acct_globals.active;
if (!file || !acct_globals.needcheck)
goto out;
spin_unlock(&acct_globals.lock);
/* May block */
if (vfs_statfs(file->f_dentry->d_inode->i_sb, &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_globals.file under us we'ld better be
* silent and _not_ touch anything.
*/
spin_lock(&acct_globals.lock);
if (file != acct_globals.file) {
if (act)
res = act>0;
goto out;
}
if (acct_globals.active) {
if (act < 0) {
acct_globals.active = 0;
printk(KERN_INFO "Process accounting paused\n");
}
} else {
if (act > 0) {
acct_globals.active = 1;
printk(KERN_INFO "Process accounting resumed\n");
}
}
del_timer(&acct_globals.timer);
acct_globals.needcheck = 0;
acct_globals.timer.expires = jiffies + ACCT_TIMEOUT*HZ;
add_timer(&acct_globals.timer);
res = acct_globals.active;
out:
spin_unlock(&acct_globals.lock);
return res;
}
/*
* Close the old accounting file (if currently open) and then replace
* it with file (if non-NULL).
*
* NOTE: acct_globals.lock MUST be held on entry and exit.
*/
static void acct_file_reopen(struct file *file)
{
struct file *old_acct = NULL;
if (acct_globals.file) {
old_acct = acct_globals.file;
del_timer(&acct_globals.timer);
acct_globals.active = 0;
acct_globals.needcheck = 0;
acct_globals.file = NULL;
}
if (file) {
acct_globals.file = file;
acct_globals.needcheck = 0;
acct_globals.active = 1;
/* It's been deleted if it was used before so this is safe */
init_timer(&acct_globals.timer);
acct_globals.timer.function = acct_timeout;
acct_globals.timer.expires = jiffies + ACCT_TIMEOUT*HZ;
add_timer(&acct_globals.timer);
}
if (old_acct) {
mnt_unpin(old_acct->f_vfsmnt);
spin_unlock(&acct_globals.lock);
do_acct_process(0, old_acct);
filp_close(old_acct, NULL);
spin_lock(&acct_globals.lock);
}
}
static int acct_on(char *name)
{
struct file *file;
int error;
/* 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_dentry->d_inode->i_mode)) {
filp_close(file, NULL);
return -EACCES;
}
if (!file->f_op->write) {
filp_close(file, NULL);
return -EIO;
}
error = security_acct(file);
if (error) {
filp_close(file, NULL);
return error;
}
spin_lock(&acct_globals.lock);
mnt_pin(file->f_vfsmnt);
acct_file_reopen(file);
spin_unlock(&acct_globals.lock);
mntput(file->f_vfsmnt); /* it's pinned, now give up active reference */
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 {
error = security_acct(NULL);
if (!error) {
spin_lock(&acct_globals.lock);
acct_file_reopen(NULL);
spin_unlock(&acct_globals.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)
{
spin_lock(&acct_globals.lock);
if (acct_globals.file && acct_globals.file->f_vfsmnt == m)
acct_file_reopen(NULL);
spin_unlock(&acct_globals.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)
{
spin_lock(&acct_globals.lock);
if (acct_globals.file &&
acct_globals.file->f_vfsmnt->mnt_sb == sb) {
acct_file_reopen(NULL);
}
spin_unlock(&acct_globals.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().
*/
/*
* do_acct_process does all actual work. Caller holds the reference to file.
*/
static void do_acct_process(long exitcode, struct file *file)
{
acct_t ac;
mm_segment_t fs;
unsigned long vsize;
unsigned long flim;
u64 elapsed;
u64 run_time;
struct timespec uptime;
/*
* First check to see if there is enough free_space to continue
* the process accounting system.
*/
if (!check_free_space(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->start_time.tv_sec*NSEC_PER_SEC
+ current->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 = xtime.tv_sec - elapsed;
ac.ac_utime = encode_comp_t(jiffies_to_AHZ(
current->signal->utime +
current->group_leader->utime));
ac.ac_stime = encode_comp_t(jiffies_to_AHZ(
current->signal->stime +
current->group_leader->stime));
/* we really need to bite the bullet and change layout */
ac.ac_uid = current->uid;
ac.ac_gid = current->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 = current->uid;
ac.ac_gid16 = current->gid;
#endif
#if ACCT_VERSION==3
ac.ac_pid = current->tgid;
ac.ac_ppid = current->parent->tgid;
#endif
read_lock(&tasklist_lock); /* pin current->signal */
ac.ac_tty = current->signal->tty ?
old_encode_dev(tty_devnum(current->signal->tty)) : 0;
read_unlock(&tasklist_lock);
ac.ac_flag = 0;
if (current->flags & PF_FORKNOEXEC)
ac.ac_flag |= AFORK;
if (current->flags & PF_SUPERPRIV)
ac.ac_flag |= ASU;
if (current->flags & PF_DUMPCORE)
ac.ac_flag |= ACORE;
if (current->flags & PF_SIGNALED)
ac.ac_flag |= AXSIG;
vsize = 0;
if (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);
}
vsize = vsize / 1024;
ac.ac_mem = encode_comp_t(vsize);
ac.ac_io = encode_comp_t(0 /* current->io_usage */); /* %% */
ac.ac_rw = encode_comp_t(ac.ac_io / 1024);
ac.ac_minflt = encode_comp_t(current->signal->min_flt +
current->group_leader->min_flt);
ac.ac_majflt = encode_comp_t(current->signal->maj_flt +
current->group_leader->maj_flt);
ac.ac_swaps = encode_comp_t(0);
ac.ac_exitcode = exitcode;
/*
* 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_process - now just a wrapper around do_acct_process
* @exitcode: task exit code
*
* handles process accounting for an exiting task
*/
void acct_process(long exitcode)
{
struct file *file = NULL;
/*
* accelerate the common fastpath:
*/
if (!acct_globals.file)
return;
spin_lock(&acct_globals.lock);
file = acct_globals.file;
if (unlikely(!file)) {
spin_unlock(&acct_globals.lock);
return;
}
get_file(file);
spin_unlock(&acct_globals.lock);
do_acct_process(exitcode, file);
fput(file);
}
/**
* acct_update_integrals - update mm integral fields in task_struct
* @tsk: task_struct for accounting
*/
void acct_update_integrals(struct task_struct *tsk)
{
if (likely(tsk->mm)) {
long delta = tsk->stime - tsk->acct_stimexpd;
if (delta == 0)
return;
tsk->acct_stimexpd = tsk->stime;
tsk->acct_rss_mem1 += delta * get_mm_rss(tsk->mm);
tsk->acct_vm_mem1 += delta * tsk->mm->total_vm;
}
}
/**
* acct_clear_integrals - clear the mm integral fields in task_struct
* @tsk: task_struct whose accounting fields are cleared
*/
void acct_clear_integrals(struct task_struct *tsk)
{
if (tsk) {
tsk->acct_stimexpd = 0;
tsk->acct_rss_mem1 = 0;
tsk->acct_vm_mem1 = 0;
}
}
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