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Bruce Fields" Cc: Olga Kornievskaia , Dai Ngo ,Tom Talpey , linux-nfs@vger.kernel.org Subject: [PATCH] nfsd: drop st_mutex before calling move_to_close_lru() Date: Fri, 22 Dec 2023 12:41:00 +1100 Message-id: <170320926037.11005.9834662167645370066@noble.neil.brown.name> X-Spam-Level: Authentication-Results: smtp-out1.suse.de; none X-Spam-Level: X-Spam-Score: -1.28 X-Spamd-Result: default: False [-1.28 / 50.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_COUNT_THREE(0.00)[3]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.18)[-0.902]; RCPT_COUNT_SEVEN(0.00)[7]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_TLS_ALL(0.00)[]; BAYES_HAM(-0.00)[10.89%] X-Spam-Flag: NO move_to_close_lru() is currently called with ->st_mutex held. This can lead to a deadlock as move_to_close_lru() waits for sc_count to drop to 2, and some threads holding a reference might be waiting for the mutex. These references will never be dropped so sc_count will never reach 2. There can be no harm in dropping ->st_mutex to before move_to_close_lru() because the only place that takes the mutex is nfsd4_lock_ol_stateid(), and it quickly aborts if sc_type is NFS4_CLOSED_STID, which it will be before move_to_close_lru() is called. See also https://lore.kernel.org/lkml/4dd1fe21e11344e5969bb112e954affb@jd.com/T/ where this problem was raised but not successfully resolved. Signed-off-by: NeilBrown --- fs/nfsd/nfs4state.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c index 40415929e2ae..1fd0c8a59cc4 100644 --- a/fs/nfsd/nfs4state.c +++ b/fs/nfsd/nfs4state.c @@ -7055,7 +7055,7 @@ nfsd4_open_downgrade(struct svc_rqst *rqstp, return status; } -static void nfsd4_close_open_stateid(struct nfs4_ol_stateid *s) +static bool nfsd4_close_open_stateid(struct nfs4_ol_stateid *s) { struct nfs4_client *clp = s->st_stid.sc_client; bool unhashed; @@ -7072,11 +7072,11 @@ static void nfsd4_close_open_stateid(struct nfs4_ol_stateid *s) list_for_each_entry(stp, &reaplist, st_locks) nfs4_free_cpntf_statelist(clp->net, &stp->st_stid); free_ol_stateid_reaplist(&reaplist); + return false; } else { spin_unlock(&clp->cl_lock); free_ol_stateid_reaplist(&reaplist); - if (unhashed) - move_to_close_lru(s, clp->net); + return unhashed; } } @@ -7092,6 +7092,7 @@ nfsd4_close(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate, struct nfs4_ol_stateid *stp; struct net *net = SVC_NET(rqstp); struct nfsd_net *nn = net_generic(net, nfsd_net_id); + bool need_move_to_close_list; dprintk("NFSD: nfsd4_close on file %pd\n", cstate->current_fh.fh_dentry); @@ -7114,8 +7115,10 @@ nfsd4_close(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate, */ nfs4_inc_and_copy_stateid(&close->cl_stateid, &stp->st_stid); - nfsd4_close_open_stateid(stp); + need_move_to_close_list = nfsd4_close_open_stateid(stp); mutex_unlock(&stp->st_mutex); + if (need_move_to_close_list) + move_to_close_lru(stp, net); /* v4.1+ suggests that we send a special stateid in here, since the * clients should just ignore this anyway. Since this is not useful