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Subject[PATCH AUTOSEL 4.9 19/33] NFSv4: Fix a potential sleep while atomic in nfs4_do_reclaim()
Date
From: Trond Myklebust <trond.myklebust@hammerspace.com>

[ Upstream commit c77e22834ae9a11891cb613bd9a551be1b94f2bc ]

John Hubbard reports seeing the following stack trace:

nfs4_do_reclaim
rcu_read_lock /* we are now in_atomic() and must not sleep */
nfs4_purge_state_owners
nfs4_free_state_owner
nfs4_destroy_seqid_counter
rpc_destroy_wait_queue
cancel_delayed_work_sync
__cancel_work_timer
__flush_work
start_flush_work
might_sleep:
(kernel/workqueue.c:2975: BUG)

The solution is to separate out the freeing of the state owners
from nfs4_purge_state_owners(), and perform that outside the atomic
context.

Reported-by: John Hubbard <jhubbard@nvidia.com>
Fixes: 0aaaf5c424c7f ("NFS: Cache state owners after files are closed")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/nfs/nfs4_fs.h | 3 ++-
fs/nfs/nfs4client.c | 5 ++++-
fs/nfs/nfs4state.c | 27 ++++++++++++++++++++++-----
3 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/fs/nfs/nfs4_fs.h b/fs/nfs/nfs4_fs.h
index 1452177c822db..c719389381dc4 100644
--- a/fs/nfs/nfs4_fs.h
+++ b/fs/nfs/nfs4_fs.h
@@ -434,7 +434,8 @@ static inline void nfs4_schedule_session_recovery(struct nfs4_session *session,

extern struct nfs4_state_owner *nfs4_get_state_owner(struct nfs_server *, struct rpc_cred *, gfp_t);
extern void nfs4_put_state_owner(struct nfs4_state_owner *);
-extern void nfs4_purge_state_owners(struct nfs_server *);
+extern void nfs4_purge_state_owners(struct nfs_server *, struct list_head *);
+extern void nfs4_free_state_owners(struct list_head *head);
extern struct nfs4_state * nfs4_get_open_state(struct inode *, struct nfs4_state_owner *);
extern void nfs4_put_open_state(struct nfs4_state *);
extern void nfs4_close_state(struct nfs4_state *, fmode_t);
diff --git a/fs/nfs/nfs4client.c b/fs/nfs/nfs4client.c
index 43f42cc30a606..1ec6dd4f3e2e4 100644
--- a/fs/nfs/nfs4client.c
+++ b/fs/nfs/nfs4client.c
@@ -781,9 +781,12 @@ int nfs41_walk_client_list(struct nfs_client *new,

static void nfs4_destroy_server(struct nfs_server *server)
{
+ LIST_HEAD(freeme);
+
nfs_server_return_all_delegations(server);
unset_pnfs_layoutdriver(server);
- nfs4_purge_state_owners(server);
+ nfs4_purge_state_owners(server, &freeme);
+ nfs4_free_state_owners(&freeme);
}

/*
diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
index 6f474b0670323..4e63daeef6339 100644
--- a/fs/nfs/nfs4state.c
+++ b/fs/nfs/nfs4state.c
@@ -611,24 +611,39 @@ void nfs4_put_state_owner(struct nfs4_state_owner *sp)
/**
* nfs4_purge_state_owners - Release all cached state owners
* @server: nfs_server with cached state owners to release
+ * @head: resulting list of state owners
*
* Called at umount time. Remaining state owners will be on
* the LRU with ref count of zero.
+ * Note that the state owners are not freed, but are added
+ * to the list @head, which can later be used as an argument
+ * to nfs4_free_state_owners.
*/
-void nfs4_purge_state_owners(struct nfs_server *server)
+void nfs4_purge_state_owners(struct nfs_server *server, struct list_head *head)
{
struct nfs_client *clp = server->nfs_client;
struct nfs4_state_owner *sp, *tmp;
- LIST_HEAD(doomed);

spin_lock(&clp->cl_lock);
list_for_each_entry_safe(sp, tmp, &server->state_owners_lru, so_lru) {
- list_move(&sp->so_lru, &doomed);
+ list_move(&sp->so_lru, head);
nfs4_remove_state_owner_locked(sp);
}
spin_unlock(&clp->cl_lock);
+}

- list_for_each_entry_safe(sp, tmp, &doomed, so_lru) {
+/**
+ * nfs4_purge_state_owners - Release all cached state owners
+ * @head: resulting list of state owners
+ *
+ * Frees a list of state owners that was generated by
+ * nfs4_purge_state_owners
+ */
+void nfs4_free_state_owners(struct list_head *head)
+{
+ struct nfs4_state_owner *sp, *tmp;
+
+ list_for_each_entry_safe(sp, tmp, head, so_lru) {
list_del(&sp->so_lru);
nfs4_free_state_owner(sp);
}
@@ -1764,12 +1779,13 @@ static int nfs4_do_reclaim(struct nfs_client *clp, const struct nfs4_state_recov
struct nfs4_state_owner *sp;
struct nfs_server *server;
struct rb_node *pos;
+ LIST_HEAD(freeme);
int status = 0;

restart:
rcu_read_lock();
list_for_each_entry_rcu(server, &clp->cl_superblocks, client_link) {
- nfs4_purge_state_owners(server);
+ nfs4_purge_state_owners(server, &freeme);
spin_lock(&clp->cl_lock);
for (pos = rb_first(&server->state_owners);
pos != NULL;
@@ -1798,6 +1814,7 @@ static int nfs4_do_reclaim(struct nfs_client *clp, const struct nfs4_state_recov
spin_unlock(&clp->cl_lock);
}
rcu_read_unlock();
+ nfs4_free_state_owners(&freeme);
return 0;
}

--
2.20.1
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