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Subject[PATCH v2.6.34-rc5 05/12] NFS: Fix RCU issues in the NFSv4 delegation code
Date
From: David Howells <dhowells@redhat.com>

Fix a number of RCU issues in the NFSv4 delegation code.

(1) delegation->cred doesn't need to be RCU protected as it's essentially an
invariant refcounted structure.

By the time we get to nfs_free_delegation(), the delegation is being
released, so no one else should be attempting to use the saved
credentials, and they can be cleared.

However, since the list of delegations could still be under traversal at
this point by such as nfs_client_return_marked_delegations(), the cred
should be released in nfs_do_free_delegation() rather than in
nfs_free_delegation(). Simply using rcu_assign_pointer() to clear it is
insufficient as that doesn't stop the cred from being destroyed, and nor
does calling put_rpccred() after call_rcu(), given that the latter is
asynchronous.

(2) nfs_detach_delegation_locked() and nfs_inode_set_delegation() should use
rcu_derefence_protected() because they can only be called if
nfs_client::cl_lock is held, and that guards against anyone changing
nfsi->delegation under it. Furthermore, the barrier imposed by
rcu_dereference() is superfluous, given that the spin_lock() is also a
barrier.

(3) nfs_detach_delegation_locked() is now passed a pointer to the nfs_client
struct so that it can issue lockdep advice based on clp->cl_lock for (2).

(4) nfs_inode_return_delegation_noreclaim() and nfs_inode_return_delegation()
should use rcu_access_pointer() outside the spinlocked region as they
merely examine the pointer and don't follow it, thus rendering unnecessary
the need to impose a partial ordering over the one item of interest.

These result in an RCU warning like the following:

[ INFO: suspicious rcu_dereference_check() usage. ]
---------------------------------------------------
fs/nfs/delegation.c:332 invoked rcu_dereference_check() without protection!
other info that might help us debug this:

rcu_scheduler_active = 1, debug_locks = 0
2 locks held by mount.nfs4/2281:
#0: (&type->s_umount_key#34){+.+...}, at: [<ffffffff810b25b4>] deactivate_super+0x60/0x80
#1: (iprune_sem){+.+...}, at: [<ffffffff810c332a>] invalidate_inodes+0x39/0x13a
stack backtrace:
Pid: 2281, comm: mount.nfs4 Not tainted 2.6.34-rc1-cachefs #110
Call Trace:
[<ffffffff8105149f>] lockdep_rcu_dereference+0xaa/0xb2
[<ffffffffa00b4591>] nfs_inode_return_delegation_noreclaim+0x5b/0xa0 [nfs]
[<ffffffffa0095d63>] nfs4_clear_inode+0x11/0x1e [nfs]
[<ffffffff810c2d92>] clear_inode+0x9e/0xf8
[<ffffffff810c3028>] dispose_list+0x67/0x10e
[<ffffffff810c340d>] invalidate_inodes+0x11c/0x13a
[<ffffffff810b1dc1>] generic_shutdown_super+0x42/0xf4
[<ffffffff810b1ebe>] kill_anon_super+0x11/0x4f
[<ffffffffa009893c>] nfs4_kill_super+0x3f/0x72 [nfs]
[<ffffffff810b25bc>] deactivate_super+0x68/0x80
[<ffffffff810c6744>] mntput_no_expire+0xbb/0xf8
[<ffffffff810c681b>] release_mounts+0x9a/0xb0
[<ffffffff810c689b>] put_mnt_ns+0x6a/0x79
[<ffffffffa00983a1>] nfs_follow_remote_path+0x5a/0x146 [nfs]
[<ffffffffa0098334>] ? nfs_do_root_mount+0x82/0x95 [nfs]
[<ffffffffa00985a9>] nfs4_try_mount+0x75/0xaf [nfs]
[<ffffffffa0098874>] nfs4_get_sb+0x291/0x31a [nfs]
[<ffffffff810b2059>] vfs_kern_mount+0xb8/0x177
[<ffffffff810b2176>] do_kern_mount+0x48/0xe8
[<ffffffff810c810b>] do_mount+0x782/0x7f9
[<ffffffff810c8205>] sys_mount+0x83/0xbe
[<ffffffff81001eeb>] system_call_fastpath+0x16/0x1b
Also on:

fs/nfs/delegation.c:215 invoked rcu_dereference_check() without protection!
[<ffffffff8105149f>] lockdep_rcu_dereference+0xaa/0xb2
[<ffffffffa00b4223>] nfs_inode_set_delegation+0xfe/0x219 [nfs]
[<ffffffffa00a9c6f>] nfs4_opendata_to_nfs4_state+0x2c2/0x30d [nfs]
[<ffffffffa00aa15d>] nfs4_do_open+0x2a6/0x3a6 [nfs]
...
And:

fs/nfs/delegation.c:40 invoked rcu_dereference_check() without protection!
[<ffffffff8105149f>] lockdep_rcu_dereference+0xaa/0xb2
[<ffffffffa00b3bef>] nfs_free_delegation+0x3d/0x6e [nfs]
[<ffffffffa00b3e71>] nfs_do_return_delegation+0x26/0x30 [nfs]
[<ffffffffa00b406a>] __nfs_inode_return_delegation+0x1ef/0x1fe [nfs]
[<ffffffffa00b448a>] nfs_client_return_marked_delegations+0xc9/0x124 [nfs]
...
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
fs/nfs/delegation.c | 44 +++++++++++++++++++++++---------------------
1 files changed, 23 insertions(+), 21 deletions(-)
diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
index 8d9ec49..ea61d26 100644
--- a/fs/nfs/delegation.c
+++ b/fs/nfs/delegation.c
@@ -24,6 +24,8 @@

static void nfs_do_free_delegation(struct nfs_delegation *delegation)
{
+ if (delegation->cred)
+ put_rpccred(delegation->cred);
kfree(delegation);
}

@@ -36,13 +38,7 @@ static void nfs_free_delegation_callback(struct rcu_head *head)

static void nfs_free_delegation(struct nfs_delegation *delegation)
{
- struct rpc_cred *cred;
-
- cred = rcu_dereference(delegation->cred);
- rcu_assign_pointer(delegation->cred, NULL);
call_rcu(&delegation->rcu, nfs_free_delegation_callback);
- if (cred)
- put_rpccred(cred);
}

void nfs_mark_delegation_referenced(struct nfs_delegation *delegation)
@@ -180,9 +176,13 @@ static struct inode *nfs_delegation_grab_inode(struct nfs_delegation *delegation
return inode;
}

-static struct nfs_delegation *nfs_detach_delegation_locked(struct nfs_inode *nfsi, const nfs4_stateid *stateid)
+static struct nfs_delegation *nfs_detach_delegation_locked(struct nfs_inode *nfsi,
+ const nfs4_stateid *stateid,
+ struct nfs_client *clp)
{
- struct nfs_delegation *delegation = rcu_dereference(nfsi->delegation);
+ struct nfs_delegation *delegation =
+ rcu_dereference_protected(nfsi->delegation,
+ lockdep_is_held(&clp->cl_lock));

if (delegation == NULL)
goto nomatch;
@@ -209,7 +209,7 @@ int nfs_inode_set_delegation(struct inode *inode, struct rpc_cred *cred, struct
{
struct nfs_client *clp = NFS_SERVER(inode)->nfs_client;
struct nfs_inode *nfsi = NFS_I(inode);
- struct nfs_delegation *delegation;
+ struct nfs_delegation *delegation, *old_delegation;
struct nfs_delegation *freeme = NULL;
int status = 0;

@@ -227,10 +227,12 @@ int nfs_inode_set_delegation(struct inode *inode, struct rpc_cred *cred, struct
spin_lock_init(&delegation->lock);

spin_lock(&clp->cl_lock);
- if (rcu_dereference(nfsi->delegation) != NULL) {
- if (memcmp(&delegation->stateid, &nfsi->delegation->stateid,
- sizeof(delegation->stateid)) == 0 &&
- delegation->type == nfsi->delegation->type) {
+ old_delegation = rcu_dereference_protected(nfsi->delegation,
+ lockdep_is_held(&clp->cl_lock));
+ if (old_delegation != NULL) {
+ if (memcmp(&delegation->stateid, &old_delegation->stateid,
+ sizeof(old_delegation->stateid)) == 0 &&
+ delegation->type == old_delegation->type) {
goto out;
}
/*
@@ -240,12 +242,12 @@ int nfs_inode_set_delegation(struct inode *inode, struct rpc_cred *cred, struct
dfprintk(FILE, "%s: server %s handed out "
"a duplicate delegation!\n",
__func__, clp->cl_hostname);
- if (delegation->type <= nfsi->delegation->type) {
+ if (delegation->type <= old_delegation->type) {
freeme = delegation;
delegation = NULL;
goto out;
}
- freeme = nfs_detach_delegation_locked(nfsi, NULL);
+ freeme = nfs_detach_delegation_locked(nfsi, NULL, clp);
}
list_add_rcu(&delegation->super_list, &clp->cl_delegations);
nfsi->delegation_state = delegation->type;
@@ -315,7 +317,7 @@ restart:
if (inode == NULL)
continue;
spin_lock(&clp->cl_lock);
- delegation = nfs_detach_delegation_locked(NFS_I(inode), NULL);
+ delegation = nfs_detach_delegation_locked(NFS_I(inode), NULL, clp);
spin_unlock(&clp->cl_lock);
rcu_read_unlock();
if (delegation != NULL) {
@@ -344,9 +346,9 @@ void nfs_inode_return_delegation_noreclaim(struct inode *inode)
struct nfs_inode *nfsi = NFS_I(inode);
struct nfs_delegation *delegation;

- if (rcu_dereference(nfsi->delegation) != NULL) {
+ if (rcu_access_pointer(nfsi->delegation) != NULL) {
spin_lock(&clp->cl_lock);
- delegation = nfs_detach_delegation_locked(nfsi, NULL);
+ delegation = nfs_detach_delegation_locked(nfsi, NULL, clp);
spin_unlock(&clp->cl_lock);
if (delegation != NULL)
nfs_do_return_delegation(inode, delegation, 0);
@@ -360,9 +362,9 @@ int nfs_inode_return_delegation(struct inode *inode)
struct nfs_delegation *delegation;
int err = 0;

- if (rcu_dereference(nfsi->delegation) != NULL) {
+ if (rcu_access_pointer(nfsi->delegation) != NULL) {
spin_lock(&clp->cl_lock);
- delegation = nfs_detach_delegation_locked(nfsi, NULL);
+ delegation = nfs_detach_delegation_locked(nfsi, NULL, clp);
spin_unlock(&clp->cl_lock);
if (delegation != NULL) {
nfs_msync_inode(inode);
@@ -540,7 +542,7 @@ restart:
if (inode == NULL)
continue;
spin_lock(&clp->cl_lock);
- delegation = nfs_detach_delegation_locked(NFS_I(inode), NULL);
+ delegation = nfs_detach_delegation_locked(NFS_I(inode), NULL, clp);
spin_unlock(&clp->cl_lock);
rcu_read_unlock();
if (delegation != NULL)
--
1.7.0


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