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nfsd: replace rp_mutex to avoid deadlock in move_to_close_lru()

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move_to_close_lru() waits for sc_count to become zero while holding
rp_mutex.  This can deadlock if another thread holds a reference and is
waiting for rp_mutex.

By the time we get to move_to_close_lru() the openowner is unhashed and
cannot be found any more.  So code waiting for the mutex can safely
retry the lookup if move_to_close_lru() has started.

So change rp_mutex to an atomic_t with three states:

 RP_UNLOCK   - state is still hashed, not locked for reply
 RP_LOCKED   - state is still hashed, is locked for reply
 RP_UNHASHED - state is not hashed, no code can get a lock.

Use wait_var_event() to wait for either a lock, or for the owner to be
unhashed.  In the latter case, retry the lookup.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
This commit is contained in:
NeilBrown 2024-04-08 12:09:17 +10:00 committed by Chuck Lever
parent b3f03739ca
commit eec7620800
2 changed files with 32 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

38
fs/nfsd/nfs4state.c
View File

@ -4650,21 +4650,32 @@ nfsd4_init_leases_net(struct nfsd_net *nn)
atomic_set(&nn->nfsd_courtesy_clients, 0);
}
enum rp_lock {
RP_UNLOCKED,
RP_LOCKED,
RP_UNHASHED,
};
static void init_nfs4_replay(struct nfs4_replay *rp)
{
rp->rp_status = nfserr_serverfault;
rp->rp_buflen = 0;
rp->rp_buf = rp->rp_ibuf;
mutex_init(&rp->rp_mutex);
atomic_set(&rp->rp_locked, RP_UNLOCKED);
}
static void nfsd4_cstate_assign_replay(struct nfsd4_compound_state *cstate,
struct nfs4_stateowner *so)
static int nfsd4_cstate_assign_replay(struct nfsd4_compound_state *cstate,
struct nfs4_stateowner *so)
{
if (!nfsd4_has_session(cstate)) {
mutex_lock(&so->so_replay.rp_mutex);
wait_var_event(&so->so_replay.rp_locked,
atomic_cmpxchg(&so->so_replay.rp_locked,
RP_UNLOCKED, RP_LOCKED) != RP_LOCKED);
if (atomic_read(&so->so_replay.rp_locked) == RP_UNHASHED)
return -EAGAIN;
cstate->replay_owner = nfs4_get_stateowner(so);
}
return 0;
}
void nfsd4_cstate_clear_replay(struct nfsd4_compound_state *cstate)
@ -4673,7 +4684,8 @@ void nfsd4_cstate_clear_replay(struct nfsd4_compound_state *cstate)
if (so != NULL) {
cstate->replay_owner = NULL;
mutex_unlock(&so->so_replay.rp_mutex);
atomic_set(&so->so_replay.rp_locked, RP_UNLOCKED);
wake_up_var(&so->so_replay.rp_locked);
nfs4_put_stateowner(so);
}
}
@ -4969,7 +4981,11 @@ move_to_close_lru(struct nfs4_ol_stateid *s, struct net *net)
* Wait for the refcount to drop to 2. Since it has been unhashed,
* there should be no danger of the refcount going back up again at
* this point.
* Some threads with a reference might be waiting for rp_locked,
* so tell them to stop waiting.
*/
atomic_set(&oo->oo_owner.so_replay.rp_locked, RP_UNHASHED);
wake_up_var(&oo->oo_owner.so_replay.rp_locked);
wait_event(close_wq, refcount_read(&s->st_stid.sc_count) == 2);
release_all_access(s);
@ -5342,11 +5358,15 @@ nfsd4_process_open1(struct nfsd4_compound_state *cstate,
clp = cstate->clp;
strhashval = ownerstr_hashval(&open->op_owner);
retry:
oo = find_or_alloc_open_stateowner(strhashval, open, cstate);
open->op_openowner = oo;
if (!oo)
return nfserr_jukebox;
nfsd4_cstate_assign_replay(cstate, &oo->oo_owner);
if (nfsd4_cstate_assign_replay(cstate, &oo->oo_owner) == -EAGAIN) {
nfs4_put_stateowner(&oo->oo_owner);
goto retry;
}
status = nfsd4_check_seqid(cstate, &oo->oo_owner, open->op_seqid);
if (status)
return status;
@ -7186,12 +7206,16 @@ nfs4_preprocess_seqid_op(struct nfsd4_compound_state *cstate, u32 seqid,
trace_nfsd_preprocess(seqid, stateid);
*stpp = NULL;
retry:
status = nfsd4_lookup_stateid(cstate, stateid,
typemask, statusmask, &s, nn);
if (status)
return status;
stp = openlockstateid(s);
nfsd4_cstate_assign_replay(cstate, stp->st_stateowner);
if (nfsd4_cstate_assign_replay(cstate, stp->st_stateowner) == -EAGAIN) {
nfs4_put_stateowner(stp->st_stateowner);
goto retry;
}
status = nfs4_seqid_op_checks(cstate, stateid, seqid, stp);
if (!status)

2
fs/nfsd/state.h
View File

@ -486,7 +486,7 @@ struct nfs4_replay {
unsigned int rp_buflen;
char *rp_buf;
struct knfsd_fh rp_openfh;
struct mutex rp_mutex;
atomic_t rp_locked;
char rp_ibuf[NFSD4_REPLAY_ISIZE];
};