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Subject[PATCH 1/2] fs: convert simple_xattrs to RCU list
Date
Use the RCU list mechanism instead of a simple lock to access/modify
simple_xattrs. The performance benefit is probably negligible, but it
will help avoid lock nesting concerns for an upcoming patch.

Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
---
fs/xattr.c | 36 ++++++++++++++++++++++--------------
include/linux/xattr.h | 1 +
2 files changed, 23 insertions(+), 14 deletions(-)

diff --git a/fs/xattr.c b/fs/xattr.c
index a1f4998bc6be..fad2344f1168 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -22,6 +22,8 @@
#include <linux/audit.h>
#include <linux/vmalloc.h>
#include <linux/posix_acl_xattr.h>
+#include <linux/rculist.h>
+#include <linux/rcupdate.h>

#include <linux/uaccess.h>

@@ -1030,8 +1032,8 @@ int simple_xattr_get(struct simple_xattrs *xattrs, const char *name,
struct simple_xattr *xattr;
int ret = -ENODATA;

- spin_lock(&xattrs->lock);
- list_for_each_entry(xattr, &xattrs->head, list) {
+ rcu_read_lock();
+ list_for_each_entry_rcu(xattr, &xattrs->head, list) {
if (strcmp(name, xattr->name))
continue;

@@ -1044,10 +1046,18 @@ int simple_xattr_get(struct simple_xattrs *xattrs, const char *name,
}
break;
}
- spin_unlock(&xattrs->lock);
+ rcu_read_unlock();
return ret;
}

+static void simple_xattr_free_rcu(struct rcu_head *rcu)
+{
+ struct simple_xattr *xattr = container_of(rcu, struct simple_xattr, rcu);
+
+ kfree(xattr->name);
+ kvfree(xattr);
+}
+
/**
* simple_xattr_set - xattr SET operation for in-memory/pseudo filesystems
* @xattrs: target simple_xattr list
@@ -1094,11 +1104,11 @@ int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
xattr = new_xattr;
err = -EEXIST;
} else if (new_xattr) {
- list_replace(&xattr->list, &new_xattr->list);
+ list_replace_rcu(&xattr->list, &new_xattr->list);
if (removed_size)
*removed_size = xattr->size;
} else {
- list_del(&xattr->list);
+ list_del_rcu(&xattr->list);
if (removed_size)
*removed_size = xattr->size;
}
@@ -1109,15 +1119,13 @@ int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
xattr = new_xattr;
err = -ENODATA;
} else {
- list_add(&new_xattr->list, &xattrs->head);
+ list_add_rcu(&new_xattr->list, &xattrs->head);
xattr = NULL;
}
out:
spin_unlock(&xattrs->lock);
- if (xattr) {
- kfree(xattr->name);
- kvfree(xattr);
- }
+ if (xattr)
+ call_rcu(&xattr->rcu, simple_xattr_free_rcu);
return err;

}
@@ -1169,8 +1177,8 @@ ssize_t simple_xattr_list(struct inode *inode, struct simple_xattrs *xattrs,
}
#endif

- spin_lock(&xattrs->lock);
- list_for_each_entry(xattr, &xattrs->head, list) {
+ rcu_read_lock();
+ list_for_each_entry_rcu(xattr, &xattrs->head, list) {
/* skip "trusted." attributes for unprivileged callers */
if (!trusted && xattr_is_trusted(xattr->name))
continue;
@@ -1179,7 +1187,7 @@ ssize_t simple_xattr_list(struct inode *inode, struct simple_xattrs *xattrs,
if (err)
break;
}
- spin_unlock(&xattrs->lock);
+ rcu_read_unlock();

return err ? err : size - remaining_size;
}
@@ -1191,6 +1199,6 @@ void simple_xattr_list_add(struct simple_xattrs *xattrs,
struct simple_xattr *new_xattr)
{
spin_lock(&xattrs->lock);
- list_add(&new_xattr->list, &xattrs->head);
+ list_add_rcu(&new_xattr->list, &xattrs->head);
spin_unlock(&xattrs->lock);
}
diff --git a/include/linux/xattr.h b/include/linux/xattr.h
index 979a9d3e5bfb..3236c469aaac 100644
--- a/include/linux/xattr.h
+++ b/include/linux/xattr.h
@@ -86,6 +86,7 @@ struct simple_xattrs {

struct simple_xattr {
struct list_head list;
+ struct rcu_head rcu;
char *name;
size_t size;
char value[];
--
2.37.2
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