New locking/refcounting for fs_struct
* 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>
diff --git a/fs/fs_struct.c b/fs/fs_struct.c
index 36e0a12..41cff72 100644
--- a/fs/fs_struct.c
+++ b/fs/fs_struct.c
@@ -72,25 +72,27 @@
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 *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 @@
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);
+ }
}