[Devel] [PATCH RHEL7 COMMIT] ms/NFSv4: Fix up RCU annotations for struct nfs_netns_client

[Vasily Averin]

The commit is pushed to "branch-rh7-3.10.0-1160.53.1.vz7.185.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1160.53.1.vz7.185.2
------>
commit 6e2dcbfe6bce56183b3303f914d8ce251839d640
Author: Trond Myklebust <trond.myklebust at hammerspace.com>
Date:   Tue Jan 25 12:38:47 2022 +0300

    ms/NFSv4: Fix up RCU annotations for struct nfs_netns_client
    
    The identifier is read as an RCU protected string. Its value may
    be changed during the lifetime of the network namespace by writing
    a new string into the sysfs pseudofile (at which point, we free the
    old string only after a call to synchronize_rcu()).
    
    Signed-off-by: Trond Myklebust <trond.myklebust at hammerspace.com>
    Signed-off-by: Anna Schumaker <Anna.Schumaker at Netapp.com>
    
    (cherry-picked from ms commit 094eca37193c516106ef8ed7f60ed058ed9fc458)
    https://jira.sw.ru/browse/PSBM-137154
    Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
---
 fs/nfs/sysfs.c | 11 ++++++++---
 fs/nfs/sysfs.h |  2 +-
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/fs/nfs/sysfs.c b/fs/nfs/sysfs.c
index c489496..8cb7075 100644
--- a/fs/nfs/sysfs.c
+++ b/fs/nfs/sysfs.c
@@ -79,7 +79,12 @@ static ssize_t nfs_netns_identifier_show(struct kobject *kobj,
 	struct nfs_netns_client *c = container_of(kobj,
 			struct nfs_netns_client,
 			kobject);
-	return scnprintf(buf, PAGE_SIZE, "%s\n", c->identifier);
+	ssize_t ret;
+
+	rcu_read_lock();
+	ret = scnprintf(buf, PAGE_SIZE, "%s\n", rcu_dereference(c->identifier));
+	rcu_read_unlock();
+	return ret;
 }
 
 /* Strip trailing '\n' */
@@ -107,7 +112,7 @@ static ssize_t nfs_netns_identifier_store(struct kobject *kobj,
 	p = kmemdup_nul(buf, len, GFP_KERNEL);
 	if (!p)
 		return -ENOMEM;
-	old = xchg(&c->identifier, p);
+	old = rcu_dereference_protected(xchg(&c->identifier, (char __rcu *)p), 1);
 	if (old) {
 		synchronize_rcu();
 		kfree(old);
@@ -121,7 +126,7 @@ static void nfs_netns_client_release(struct kobject *kobj)
 			struct nfs_netns_client,
 			kobject);
 
-	kfree(c->identifier);
+	kfree(rcu_dereference_raw(c->identifier));
 	kfree(c);
 }
 
diff --git a/fs/nfs/sysfs.h b/fs/nfs/sysfs.h
index f1b2741..b1408e6 100644
--- a/fs/nfs/sysfs.h
+++ b/fs/nfs/sysfs.h
@@ -11,7 +11,7 @@
 struct nfs_netns_client {
 	struct kobject kobject;
 	struct net *net;
-	const char *identifier;
+	const char __rcu *identifier;
 };
 
 extern struct kobject *nfs_client_kobj;