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authorNick Piggin <npiggin@kernel.dk>2010-08-18 04:37:33 +1000
committerAl Viro <viro@zeniv.linux.org.uk>2010-08-18 08:35:46 -0400
commit2a4419b5b2a77f3f4537c14f7ad7df95770655dd (patch)
treead66519a92b995920ecada788e4a08e265747545 /fs
parent44672e4fbd40e2dda8bbce7d0f71d24dbfc7e00e (diff)
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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: Nick Piggin <npiggin@kernel.dk> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs')
-rw-r--r--fs/exec.c4
-rw-r--r--fs/fs_struct.c32
2 files changed, 18 insertions, 18 deletions
diff --git a/fs/exec.c b/fs/exec.c
index 7761837e450..5adab2c93ec 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -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;
}
diff --git a/fs/fs_struct.c b/fs/fs_struct.c
index 1ee40eb9a2c..ed45a9cf5f3 100644
--- a/fs/fs_struct.c
+++ b/fs/fs_struct.c
@@ -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)