Commit 2a4419b5 authored by Nick Piggin's avatar Nick Piggin Committed by Al Viro
Browse files

fs: fs_struct rwlock to spinlock 



fs: fs_struct rwlock to spinlock

struct fs_struct.lock is an rwlock with the read-side used to protect root and
pwd members while taking references to them. Taking a reference to a path
typically requires just 2 atomic ops, so the critical section is very small.
Parallel read-side operations would have cacheline contention on the lock, the
dentry, and the vfsmount cachelines, so the rwlock is unlikely to ever give a
real parallelism increase.

Replace it with a spinlock to avoid one or two atomic operations in typical
path lookup fastpath.

Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 44672e4f

drivers/staging/pohmelfs/path_entry.c

+4 −4
Original line number Diff line number Diff line
@@ -44,9 +44,9 @@ int pohmelfs_construct_path_string(struct pohmelfs_inode *pi, void *data, int le 
		return -ENOENT;

	}



	read_lock(&current->fs->lock);

	spin_lock(&current->fs->lock);

	path.mnt = mntget(current->fs->root.mnt);

	read_unlock(&current->fs->lock);

	spin_unlock(&current->fs->lock);



	path.dentry = d;
@@ -91,9 +91,9 @@ int pohmelfs_path_length(struct pohmelfs_inode *pi) 
		return -ENOENT;

	}



	read_lock(&current->fs->lock);

	spin_lock(&current->fs->lock);

	root = dget(current->fs->root.dentry);

	read_unlock(&current->fs->lock);

	spin_unlock(&current->fs->lock);



	spin_lock(&dcache_lock);

fs/exec.c

+2 −2
Original line number Diff line number Diff line
@@ -1117,7 +1117,7 @@ int check_unsafe_exec(struct linux_binprm *bprm) 
	bprm->unsafe = tracehook_unsafe_exec(p);



	n_fs = 1;

	write_lock(&p->fs->lock);

	spin_lock(&p->fs->lock);

	rcu_read_lock();

	for (t = next_thread(p); t != p; t = next_thread(t)) {

		if (t->fs == p->fs)
@@ -1134,7 +1134,7 @@ int check_unsafe_exec(struct linux_binprm *bprm) 
			res = 1;

		}

	}

	write_unlock(&p->fs->lock);

	spin_unlock(&p->fs->lock);



	return res;

}

fs/fs_struct.c

+16 −16
Original line number Diff line number Diff line
@@ -13,11 +13,11 @@ void set_fs_root(struct fs_struct *fs, struct path *path) 
{

	struct path old_root;



	write_lock(&fs->lock);

	spin_lock(&fs->lock);

	old_root = fs->root;

	fs->root = *path;

	path_get(path);

	write_unlock(&fs->lock);

	spin_unlock(&fs->lock);

	if (old_root.dentry)

		path_put(&old_root);

}
@@ -30,11 +30,11 @@ void set_fs_pwd(struct fs_struct *fs, struct path *path) 
{

	struct path old_pwd;



	write_lock(&fs->lock);

	spin_lock(&fs->lock);

	old_pwd = fs->pwd;

	fs->pwd = *path;

	path_get(path);

	write_unlock(&fs->lock);

	spin_unlock(&fs->lock);



	if (old_pwd.dentry)

		path_put(&old_pwd);
@@ -51,7 +51,7 @@ void chroot_fs_refs(struct path *old_root, struct path *new_root) 
		task_lock(p);

		fs = p->fs;

		if (fs) {

			write_lock(&fs->lock);

			spin_lock(&fs->lock);

			if (fs->root.dentry == old_root->dentry

			    && fs->root.mnt == old_root->mnt) {

				path_get(new_root);
@@ -64,7 +64,7 @@ void chroot_fs_refs(struct path *old_root, struct path *new_root) 
				fs->pwd = *new_root;

				count++;

			}

			write_unlock(&fs->lock);

			spin_unlock(&fs->lock);

		}

		task_unlock(p);

	} while_each_thread(g, p);
@@ -87,10 +87,10 @@ void exit_fs(struct task_struct *tsk) 
	if (fs) {

		int kill;

		task_lock(tsk);

		write_lock(&fs->lock);

		spin_lock(&fs->lock);

		tsk->fs = NULL;

		kill = !--fs->users;

		write_unlock(&fs->lock);

		spin_unlock(&fs->lock);

		task_unlock(tsk);

		if (kill)

			free_fs_struct(fs);
@@ -104,7 +104,7 @@ struct fs_struct *copy_fs_struct(struct fs_struct *old) 
	if (fs) {

		fs->users = 1;

		fs->in_exec = 0;

		rwlock_init(&fs->lock);

		spin_lock_init(&fs->lock);

		fs->umask = old->umask;

		get_fs_root_and_pwd(old, &fs->root, &fs->pwd);

	}
@@ -121,10 +121,10 @@ int unshare_fs_struct(void) 
		return -ENOMEM;



	task_lock(current);

	write_lock(&fs->lock);

	spin_lock(&fs->lock);

	kill = !--fs->users;

	current->fs = new_fs;

	write_unlock(&fs->lock);

	spin_unlock(&fs->lock);

	task_unlock(current);



	if (kill)
@@ -143,7 +143,7 @@ EXPORT_SYMBOL(current_umask); 
/* to be mentioned only in INIT_TASK */

struct fs_struct init_fs = {

	.users		= 1,

	.lock		= __RW_LOCK_UNLOCKED(init_fs.lock),

	.lock		= __SPIN_LOCK_UNLOCKED(init_fs.lock),

	.umask		= 0022,

};
@@ -156,14 +156,14 @@ void daemonize_fs_struct(void) 


		task_lock(current);



		write_lock(&init_fs.lock);

		spin_lock(&init_fs.lock);

		init_fs.users++;

		write_unlock(&init_fs.lock);

		spin_unlock(&init_fs.lock);



		write_lock(&fs->lock);

		spin_lock(&fs->lock);

		current->fs = &init_fs;

		kill = !--fs->users;

		write_unlock(&fs->lock);

		spin_unlock(&fs->lock);



		task_unlock(current);

		if (kill)

include/linux/fs_struct.h

+7 −7
Original line number Diff line number Diff line
@@ -5,7 +5,7 @@ 


struct fs_struct {

	int users;

	rwlock_t lock;

	spinlock_t lock;

	int umask;

	int in_exec;

	struct path root, pwd;
@@ -23,29 +23,29 @@ extern int unshare_fs_struct(void); 


static inline void get_fs_root(struct fs_struct *fs, struct path *root)

{

	read_lock(&fs->lock);

	spin_lock(&fs->lock);

	*root = fs->root;

	path_get(root);

	read_unlock(&fs->lock);

	spin_unlock(&fs->lock);

}



static inline void get_fs_pwd(struct fs_struct *fs, struct path *pwd)

{

	read_lock(&fs->lock);

	spin_lock(&fs->lock);

	*pwd = fs->pwd;

	path_get(pwd);

	read_unlock(&fs->lock);

	spin_unlock(&fs->lock);

}



static inline void get_fs_root_and_pwd(struct fs_struct *fs, struct path *root,

				       struct path *pwd)

{

	read_lock(&fs->lock);

	spin_lock(&fs->lock);

	*root = fs->root;

	path_get(root);

	*pwd = fs->pwd;

	path_get(pwd);

	read_unlock(&fs->lock);

	spin_unlock(&fs->lock);

}



#endif /* _LINUX_FS_STRUCT_H */

kernel/fork.c

+5 −5
Original line number Diff line number Diff line
@@ -752,13 +752,13 @@ static int copy_fs(unsigned long clone_flags, struct task_struct *tsk) 
	struct fs_struct *fs = current->fs;

	if (clone_flags & CLONE_FS) {

		/* tsk->fs is already what we want */

		write_lock(&fs->lock);

		spin_lock(&fs->lock);

		if (fs->in_exec) {

			write_unlock(&fs->lock);

			spin_unlock(&fs->lock);

			return -EAGAIN;

		}

		fs->users++;

		write_unlock(&fs->lock);

		spin_unlock(&fs->lock);

		return 0;

	}

	tsk->fs = copy_fs_struct(fs);
@@ -1676,13 +1676,13 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags) 


		if (new_fs) {

			fs = current->fs;

			write_lock(&fs->lock);

			spin_lock(&fs->lock);

			current->fs = new_fs;

			if (--fs->users)

				new_fs = NULL;

			else

				new_fs = fs;

			write_unlock(&fs->lock);

			spin_unlock(&fs->lock);

		}



		if (new_mm) {

CRA Git | Maintained and supported by SUSTech CRA and CCSE