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nfs_localio: protect race between nfs_uuid_put() and nfs_close_local_fh()

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nfs_uuid_put() and nfs_close_local_fh() can race if a "struct
nfs_file_localio" is released at the same time that nfsd calls
nfs_localio_invalidate_clients().

It is important that neither of these functions completes after the
other has started looking at a given nfs_file_localio and before it
finishes.

If nfs_uuid_put() exits while nfs_close_local_fh() is closing ro_file
and rw_file it could return to __nfd_file_cache_purge() while some files
are still referenced so the purge may not succeed.

If nfs_close_local_fh() exits while nfsd_uuid_put() is still closing the
files then the "struct nfs_file_localio" could be freed while
nfsd_uuid_put() is still looking at it.  This side is currently handled
by copying the pointers out of ro_file and rw_file before deleting from
the list in nfsd_uuid.  We need to preserve this while ensuring that
nfsd_uuid_put() does wait for nfs_close_local_fh().

This patch use nfl->uuid and nfl->list to provide the required
interlock.

nfs_uuid_put() removes the nfs_file_localio from the list, then drops
locks and puts the two files, then reclaims the spinlock and sets
->nfs_uuid to NULL.

nfs_close_local_fh() operates in the reverse order, setting ->nfs_uuid
to NULL, then closing the files, then unlinking from the list.

If nfs_uuid_put() finds that ->nfs_uuid is already NULL, it waits for
the nfs_file_localio to be removed from the list.  If
nfs_close_local_fh() find that it has already been unlinked it waits for
->nfs_uuid to become NULL.  This ensure that one of the two tries to
close the files, but they each waits for the other.

As nfs_uuid_put() is making the list empty, change from a
list_for_each_safe loop to a while that always takes the first entry.
This makes the intent more clear.
Also don't move the list to a temporary local list as this would defeat
the guarantees required for the interlock.

Fixes: 86e0041225 ("nfs: cache all open LOCALIO nfsd_file(s) in client")
Signed-off-by: NeilBrown <neil@brown.name>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
This commit is contained in:
NeilBrown 2025-05-09 10:46:42 +10:00 • committed by Anna Schumaker
parent 74fc55ab2a
commit 21fb440346
1 changed files with 56 additions and 25 deletions
Download patch file Download diff file Expand all files Collapse all files

77
fs/nfs_common/nfslocalio.c
View file

@ -151,8 +151,7 @@ EXPORT_SYMBOL_GPL(nfs_localio_enable_client);
*/
static bool nfs_uuid_put(nfs_uuid_t *nfs_uuid)
{
LIST_HEAD(local_files);
struct nfs_file_localio *nfl, *tmp;
struct nfs_file_localio *nfl;
spin_lock(&nfs_uuid->lock);
if (unlikely(!rcu_access_pointer(nfs_uuid->net))) {
@ -166,36 +165,48 @@ static bool nfs_uuid_put(nfs_uuid_t *nfs_uuid)
nfs_uuid->dom = NULL;
}
list_splice_init(&nfs_uuid->files, &local_files);
spin_unlock(&nfs_uuid->lock);
/* Walk list of files and ensure their last references dropped */
list_for_each_entry_safe(nfl, tmp, &local_files, list) {
while ((nfl = list_first_entry_or_null(&nfs_uuid->files,
struct nfs_file_localio,
list)) != NULL) {
struct nfsd_file *ro_nf;
struct nfsd_file *rw_nf;
/* If nfs_uuid is already NULL, nfs_close_local_fh is
* closing and we must wait, else we unlink and close.
*/
if (rcu_access_pointer(nfl->nfs_uuid) == NULL) {
/* nfs_close_local_fh() is doing the
* close and we must wait. until it unlinks
*/
wait_var_event_spinlock(nfl,
list_first_entry_or_null(
&nfs_uuid->files,
struct nfs_file_localio,
list) != nfl,
&nfs_uuid->lock);
continue;
}
ro_nf = unrcu_pointer(xchg(&nfl->ro_file, NULL));
rw_nf = unrcu_pointer(xchg(&nfl->rw_file, NULL));
spin_lock(&nfs_uuid->lock);
/* Remove nfl from nfs_uuid->files list */
list_del_init(&nfl->list);
spin_unlock(&nfs_uuid->lock);
/* Now we can allow racing nfs_close_local_fh() to
* skip the locking.
*/
RCU_INIT_POINTER(nfl->nfs_uuid, NULL);
if (ro_nf)
nfs_to_nfsd_file_put_local(ro_nf);
if (rw_nf)
nfs_to_nfsd_file_put_local(rw_nf);
cond_resched();
}
spin_lock(&nfs_uuid->lock);
BUG_ON(!list_empty(&nfs_uuid->files));
/* Now we can allow racing nfs_close_local_fh() to
* skip the locking.
*/
RCU_INIT_POINTER(nfl->nfs_uuid, NULL);
wake_up_var_locked(&nfl->nfs_uuid, &nfs_uuid->lock);
}
/* Remove client from nn->local_clients */
if (nfs_uuid->list_lock) {
@ -304,23 +315,43 @@ void nfs_close_local_fh(struct nfs_file_localio *nfl)
return;
}
ro_nf = unrcu_pointer(xchg(&nfl->ro_file, NULL));
rw_nf = unrcu_pointer(xchg(&nfl->rw_file, NULL));
spin_lock(&nfs_uuid->lock);
/* Remove nfl from nfs_uuid->files list */
list_del_init(&nfl->list);
if (!rcu_access_pointer(nfl->nfs_uuid)) {
/* nfs_uuid_put has finished here */
spin_unlock(&nfs_uuid->lock);
rcu_read_unlock();
/* Now we can allow racing nfs_close_local_fh() to
* skip the locking.
return;
}
if (list_empty(&nfs_uuid->files)) {
/* nfs_uuid_put() has started closing files, wait for it
* to finished
*/
spin_unlock(&nfs_uuid->lock);
rcu_read_unlock();
wait_var_event(&nfl->nfs_uuid,
rcu_access_pointer(nfl->nfs_uuid) == NULL);
return;
}
/* tell nfs_uuid_put() to wait for us */
RCU_INIT_POINTER(nfl->nfs_uuid, NULL);
spin_unlock(&nfs_uuid->lock);
rcu_read_unlock();
ro_nf = unrcu_pointer(xchg(&nfl->ro_file, NULL));
rw_nf = unrcu_pointer(xchg(&nfl->rw_file, NULL));
if (ro_nf)
nfs_to_nfsd_file_put_local(ro_nf);
if (rw_nf)
nfs_to_nfsd_file_put_local(rw_nf);
/* Remove nfl from nfs_uuid->files list and signal nfs_uuid_put()
* that we are done. The moment we drop the spinlock the
* nfs_uuid could be freed.
*/
spin_lock(&nfs_uuid->lock);
list_del_init(&nfl->list);
wake_up_var_locked(&nfl->nfs_uuid, &nfs_uuid->lock);
spin_unlock(&nfs_uuid->lock);
}
EXPORT_SYMBOL_GPL(nfs_close_local_fh);