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fs: fs_struct rwlock to spinlock

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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: Nick Piggin <npiggin@kernel.dk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Nick Piggin
2010-08-18 04:37:33 +10:00
committed by Al Viro
parent 44672e4fbd
commit 2a4419b5b2
5 changed files with 34 additions and 34 deletions
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32
fs/fs_struct.c
View File

@@ -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)