fs: dcache scale subdirs
Protect d_subdirs and d_child with d_lock, except in filesystems that aren't
using dcache_lock for these anyway (eg. using i_mutex).
Note: if we change the locking rule in future so that ->d_child protection is
provided only with ->d_parent->d_lock, it may allow us to reduce some locking.
But it would be an exception to an otherwise regular locking scheme, so we'd
have to see some good results. Probably not worthwhile.
Signed-off-by: Nick Piggin <npiggin@kernel.dk>
diff --git a/fs/libfs.c b/fs/libfs.c
index 433e713..cc47949 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -81,7 +81,8 @@
loff_t dcache_dir_lseek(struct file *file, loff_t offset, int origin)
{
- mutex_lock(&file->f_path.dentry->d_inode->i_mutex);
+ struct dentry *dentry = file->f_path.dentry;
+ mutex_lock(&dentry->d_inode->i_mutex);
switch (origin) {
case 1:
offset += file->f_pos;
@@ -89,7 +90,7 @@
if (offset >= 0)
break;
default:
- mutex_unlock(&file->f_path.dentry->d_inode->i_mutex);
+ mutex_unlock(&dentry->d_inode->i_mutex);
return -EINVAL;
}
if (offset != file->f_pos) {
@@ -100,22 +101,25 @@
loff_t n = file->f_pos - 2;
spin_lock(&dcache_lock);
+ spin_lock(&dentry->d_lock);
+ /* d_lock not required for cursor */
list_del(&cursor->d_u.d_child);
- p = file->f_path.dentry->d_subdirs.next;
- while (n && p != &file->f_path.dentry->d_subdirs) {
+ p = dentry->d_subdirs.next;
+ while (n && p != &dentry->d_subdirs) {
struct dentry *next;
next = list_entry(p, struct dentry, d_u.d_child);
- spin_lock(&next->d_lock);
+ spin_lock_nested(&next->d_lock, DENTRY_D_LOCK_NESTED);
if (simple_positive(next))
n--;
spin_unlock(&next->d_lock);
p = p->next;
}
list_add_tail(&cursor->d_u.d_child, p);
+ spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
}
}
- mutex_unlock(&file->f_path.dentry->d_inode->i_mutex);
+ mutex_unlock(&dentry->d_inode->i_mutex);
return offset;
}
@@ -156,6 +160,7 @@
/* fallthrough */
default:
spin_lock(&dcache_lock);
+ spin_lock(&dentry->d_lock);
if (filp->f_pos == 2)
list_move(q, &dentry->d_subdirs);
@@ -169,6 +174,7 @@
}
spin_unlock(&next->d_lock);
+ spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
if (filldir(dirent, next->d_name.name,
next->d_name.len, filp->f_pos,
@@ -176,11 +182,15 @@
dt_type(next->d_inode)) < 0)
return 0;
spin_lock(&dcache_lock);
+ spin_lock(&dentry->d_lock);
+ spin_lock_nested(&next->d_lock, DENTRY_D_LOCK_NESTED);
/* next is still alive */
list_move(q, p);
+ spin_unlock(&next->d_lock);
p = q;
filp->f_pos++;
}
+ spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
}
return 0;
@@ -276,6 +286,7 @@
int ret = 0;
spin_lock(&dcache_lock);
+ spin_lock(&dentry->d_lock);
list_for_each_entry(child, &dentry->d_subdirs, d_u.d_child) {
spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
if (simple_positive(child)) {
@@ -286,6 +297,7 @@
}
ret = 1;
out:
+ spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
return ret;
}