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Mon, 8 Apr 2024 02:12:26 +0000 (UTC) Received: from dovecot-director2.suse.de ([10.150.64.162]) by imap1.dmz-prg2.suse.org with ESMTPSA id LfSTIopSE2YHEgAAD6G6ig (envelope-from ); Mon, 08 Apr 2024 02:12:26 +0000 From: NeilBrown To: Chuck Lever , Jeff Layton Cc: linux-nfs@vger.kernel.org, Olga Kornievskaia , Dai Ngo , Tom Talpey Subject: [PATCH 3/4] nfsd: replace rp_mutex to avoid deadlock in move_to_close_lru() Date: Mon, 8 Apr 2024 12:09:17 +1000 Message-ID: <20240408021156.6104-4-neilb@suse.de> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20240408021156.6104-1-neilb@suse.de> References: <20240408021156.6104-1-neilb@suse.de> Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Flag: NO X-Spam-Score: -3.01 X-Rspamd-Action: no action X-Rspamd-Queue-Id: 92CF321851 X-Spam-Level: X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Spamd-Result: default: False [-3.01 / 50.00]; BAYES_HAM(-3.00)[100.00%]; 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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 Signed-off-by: NeilBrown --- fs/nfsd/nfs4state.c | 38 +++++++++++++++++++++++++++++++------- fs/nfsd/state.h | 2 +- 2 files changed, 32 insertions(+), 8 deletions(-) diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c index 2ff8cb50f2e3..5dbd1a73bc28 100644 --- a/fs/nfsd/nfs4state.c +++ b/fs/nfsd/nfs4state.c @@ -4664,21 +4664,32 @@ 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) @@ -4687,7 +4698,8 @@ 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); } } @@ -4983,7 +4995,11 @@ 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); @@ -5356,11 +5372,15 @@ 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; @@ -7200,12 +7220,16 @@ 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) diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h index 7f33b89f3b2c..f42d8d782c84 100644 --- a/fs/nfsd/state.h +++ b/fs/nfsd/state.h @@ -488,7 +488,7 @@ 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]; }; -- 2.44.0