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New locking/refcounting for fs_struct

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* all changes of current->fs are done under task_lock and write_lock of
  old fs->lock
* refcount is not atomic anymore (same protection)
* its decrements are done when removing reference from current; at the
  same time we decide whether to free it.
* put_fs_struct() is gone
* new field - ->in_exec.  Set by check_unsafe_exec() if we are trying to do
  execve() and only subthreads share fs_struct.  Cleared when finishing exec
  (success and failure alike).  Makes CLONE_FS fail with -EAGAIN if set.
* check_unsafe_exec() may fail with -EAGAIN if another execve() from subthread
  is in progress.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro
2009-03-30 07:20:30 -04:00
parent 3e93cd6718
commit 498052bba5
7 changed files with 121 additions and 44 deletions
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69
fs/fs_struct.c
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@@ -72,25 +72,27 @@ void chroot_fs_refs(struct path *old_root, struct path *new_root)
path_put(old_root);
}
void put_fs_struct(struct fs_struct *fs)
void free_fs_struct(struct fs_struct *fs)
{
/* No need to hold fs->lock if we are killing it */
if (atomic_dec_and_test(&fs->count)) {
path_put(&fs->root);
path_put(&fs->pwd);
kmem_cache_free(fs_cachep, fs);
}
path_put(&fs->root);
path_put(&fs->pwd);
kmem_cache_free(fs_cachep, fs);
}
void exit_fs(struct task_struct *tsk)
{
struct fs_struct * fs = tsk->fs;
struct fs_struct *fs = tsk->fs;
if (fs) {
int kill;
task_lock(tsk);
write_lock(&fs->lock);
tsk->fs = NULL;
kill = !--fs->users;
write_unlock(&fs->lock);
task_unlock(tsk);
put_fs_struct(fs);
if (kill)
free_fs_struct(fs);
}
}
@@ -99,7 +101,8 @@ struct fs_struct *copy_fs_struct(struct fs_struct *old)
struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL);
/* We don't need to lock fs - think why ;-) */
if (fs) {
atomic_set(&fs->count, 1);
fs->users = 1;
fs->in_exec = 0;
rwlock_init(&fs->lock);
fs->umask = old->umask;
read_lock(&old->lock);
@@ -114,28 +117,54 @@ struct fs_struct *copy_fs_struct(struct fs_struct *old)
int unshare_fs_struct(void)
{
struct fs_struct *fsp = copy_fs_struct(current->fs);
if (!fsp)
struct fs_struct *fs = current->fs;
struct fs_struct *new_fs = copy_fs_struct(fs);
int kill;
if (!new_fs)
return -ENOMEM;
exit_fs(current);
current->fs = fsp;
task_lock(current);
write_lock(&fs->lock);
kill = !--fs->users;
current->fs = new_fs;
write_unlock(&fs->lock);
task_unlock(current);
if (kill)
free_fs_struct(fs);
return 0;
}
EXPORT_SYMBOL_GPL(unshare_fs_struct);
/* to be mentioned only in INIT_TASK */
struct fs_struct init_fs = {
.count = ATOMIC_INIT(1),
.users = 1,
.lock = __RW_LOCK_UNLOCKED(init_fs.lock),
.umask = 0022,
};
void daemonize_fs_struct(void)
{
struct fs_struct *fs;
struct fs_struct *fs = current->fs;
exit_fs(current); /* current->fs->count--; */
fs = &init_fs;
current->fs = fs;
atomic_inc(&fs->count);
if (fs) {
int kill;
task_lock(current);
write_lock(&init_fs.lock);
init_fs.users++;
write_unlock(&init_fs.lock);
write_lock(&fs->lock);
current->fs = &init_fs;
kill = !--fs->users;
write_unlock(&fs->lock);
task_unlock(current);
if (kill)
free_fs_struct(fs);
}
}