NFS: Fix dentry revalidation on NFSv4 lookup [Linux 4.19.64]

This Linux kernel change "NFS: Fix dentry revalidation on NFSv4 lookup" is included in the Linux 4.19.64 release. This change is authored by Trond Myklebust <trond.myklebust [at] hammerspace.com> on Thu Sep 27 17:12:33 2018 -0400. The commit for this change in Linux stable tree is 01eea1c (patch) which is from upstream commit be189f7. The same Linux upstream change may have been applied to various maintained Linux releases and you can find all Linux releases containing changes from upstream be189f7.

NFS: Fix dentry revalidation on NFSv4 lookup

commit be189f7e7f03de35887e5a85ddcf39b91b5d7fc1 upstream.

We need to ensure that inode and dentry revalidation occurs correctly
on reopen of a file that is already open. Currently, we can end up
not revalidating either in the case of NFSv4.0, due to the 'cached open'
path.
Let's fix that by ensuring that we only do cached open for the special
cases of open recovery and delegation return.

Reported-by: Stan Hu <stanhu@gmail.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Qian Lu <luqia@amazon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

There are 15 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 fs/nfs/nfs4proc.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 1de855e..904e08b 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -1355,12 +1355,20 @@ static bool nfs4_mode_match_open_stateid(struct nfs4_state *state,
    return false;
 }

-static int can_open_cached(struct nfs4_state *state, fmode_t mode, int open_mode)
+static int can_open_cached(struct nfs4_state *state, fmode_t mode,
+       int open_mode, enum open_claim_type4 claim)
 {
    int ret = 0;

    if (open_mode & (O_EXCL|O_TRUNC))
        goto out;
+   switch (claim) {
+   case NFS4_OPEN_CLAIM_NULL:
+   case NFS4_OPEN_CLAIM_FH:
+       goto out;
+   default:
+       break;
+   }
    switch (mode & (FMODE_READ|FMODE_WRITE)) {
        case FMODE_READ:
            ret |= test_bit(NFS_O_RDONLY_STATE, &state->flags) != 0
@@ -1753,7 +1761,7 @@ static struct nfs4_state *nfs4_try_open_cached(struct nfs4_opendata *opendata)

    for (;;) {
        spin_lock(&state->owner->so_lock);
-       if (can_open_cached(state, fmode, open_mode)) {
+       if (can_open_cached(state, fmode, open_mode, claim)) {
            update_open_stateflags(state, fmode);
            spin_unlock(&state->owner->so_lock);
            goto out_return_state;
@@ -2282,7 +2290,8 @@ static void nfs4_open_prepare(struct rpc_task *task, void *calldata)
    if (data->state != NULL) {
        struct nfs_delegation *delegation;

-       if (can_open_cached(data->state, data->o_arg.fmode, data->o_arg.open_flags))
+       if (can_open_cached(data->state, data->o_arg.fmode,
+                   data->o_arg.open_flags, claim))
            goto out_no_action;
        rcu_read_lock();
        delegation = rcu_dereference(NFS_I(data->state->inode)->delegation);

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