diff options
| author | NeilBrown <neil@brown.name> | 2025-05-09 10:46:42 +1000 |
|---|---|---|
| committer | Anna Schumaker <anna.schumaker@oracle.com> | 2025-05-28 17:17:14 -0400 |
| commit | 21fb44034695185f1dcbcb37354c842cabfe83c1 (patch) | |
| tree | 212c834ace451db185c58c64bb5a631d3171d8c0 /fs | |
| parent | 74fc55ab2a6a0c71628fcf3b9783aae7119b5199 (diff) | |
| download | linux-21fb44034695185f1dcbcb37354c842cabfe83c1.tar.gz | |
nfs_localio: protect race between nfs_uuid_put() and nfs_close_local_fh()
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: 86e00412254a ("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>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/nfs_common/nfslocalio.c | 81 |
1 files changed, 56 insertions, 25 deletions
diff --git a/fs/nfs_common/nfslocalio.c b/fs/nfs_common/nfslocalio.c index 49c59f0c78c629..1dd5a8cca064d8 100644 --- a/fs/nfs_common/nfslocalio.c +++ b/fs/nfs_common/nfslocalio.c @@ -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))) { @@ -166,37 +165,49 @@ 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); + /* 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); } - spin_lock(&nfs_uuid->lock); - BUG_ON(!list_empty(&nfs_uuid->files)); - /* Remove client from nn->local_clients */ if (nfs_uuid->list_lock) { spin_lock(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(); + 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(); - /* Now we can allow racing nfs_close_local_fh() to - * skip the locking. - */ - RCU_INIT_POINTER(nfl->nfs_uuid, NULL); + 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); |