From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5AC6D369D43; Fri, 12 Jun 2026 18:36:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781289371; cv=none; b=Ur6zhmkctqHM5MULEZsJr5pKertBMU/1R7pwdJ7GnrlBsVvKkK6juWjRBH8e8okM4Iy0Uqul1o8fa1U5mjxheYRxOIUIVsZqIxU0hFKR89d1PFdp7Dy3geG/jgqNMyCWdhKyQa4DaCgUZyDmxgnCugiS9e/UUxFYP75MAqmEuh4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781289371; c=relaxed/simple; bh=FsKCZjNbYaHzjYp5mZSgPaQ3xRkP8w4McKrXM0ieuJ0=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=aMyBJ3L+8HgMjJyNBE32F47UdTgC7SLjIAFJwfza/Mpu0/lmXVxO9chHKTcL51XAwkrBp/rx/z/NqN2kggOtdgnpvGDnUGXNnT+TJSsVOccGZEVvy6F4hHiHlWBEzAp3cAvKt343Z1mG9YzWMAb+dJKZNHTFcL4VZ7+yTysYeC4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=nYfMkxqn; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="nYfMkxqn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 323081F000E9; Fri, 12 Jun 2026 18:36:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781289370; bh=6JRIp+0ZnHXaXJITWv4qytluPS2XYOyFtxmiaDvmY9Y=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=nYfMkxqncfS1V/SVPfxgd6qeCZgbmZXJt+JTxpHFMqVdWzi2WGqDyy/PCsDNsqakc fmPwP2lT/wwuWpKcysUSW60X2Ug+hzm9fdccLUpWL14tYGhl5keiupZbJacHGjp7fd vdsnGn5K1jZE47BqaW2sWYifEcmlnwJDYu1OyrKxpiCgq2dZydLAz5SDQ5rCSgARUS 21hCC/NnTyNpn6mi3BOX/98mmgnZqbabNNuMwgVM56KxNot7Du7QI46UCtrIkd+pKB 0qM6fjj8kT1lsBbofNyLxmnyl5ujvP3xqqVDAQ3M7cCUK2lEqluT4NUSYR+IMdT7Xr w6bh/r68qfqbw== Message-ID: Subject: Re: [PATCH v6 10/20] nfsd: add notification handlers for dir events From: Jeff Layton To: Chuck Lever , NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey , Trond Myklebust , Anna Schumaker , Jonathan Corbet , Shuah Khan Cc: Steven Rostedt , Alexander Aring , Amir Goldstein , Jan Kara , Alexander Viro , Christian Brauner , Calum Mackay , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-nfs@vger.kernel.org Date: Fri, 12 Jun 2026 14:36:06 -0400 In-Reply-To: References: <20260611-dir-deleg-v6-0-4c45080e5f3f@kernel.org> <20260611-dir-deleg-v6-10-4c45080e5f3f@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv 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linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, 2026-06-12 at 13:51 -0400, Chuck Lever wrote: > On Thu, Jun 11, 2026, at 1:50 PM, Jeff Layton wrote: > > Add the necessary parts to accept a fsnotify callback for directory > > change event and create a CB_NOTIFY request for it. When a dir nfsd_fil= e > > is created set a handle_event callback to handle the notification. > >=20 > > Use that to allocate a nfsd_notify_event object and then hand off a > > reference to each delegation's CB_NOTIFY. If anything fails along the > > way, recall any affected delegations. > >=20 > > Signed-off-by: Jeff Layton > > --- >=20 > > diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c > > index ca4dd2f969eb..59378751d596 100644 > > --- a/fs/nfsd/nfs4callback.c > > +++ b/fs/nfsd/nfs4callback.c >=20 > > @@ -904,13 +908,45 @@ static void nfs4_xdr_enc_cb_notify(struct rpc_rqs= t *req, > > encode_cb_sequence4args(xdr, cb, &hdr); > >=20 > > /* > > - * FIXME: get stateid and fh from delegation. Inline the cna_changes > > - * buffer, and zero it. > > + * nfsd4_cb_notify_prepare() sized the payload against a single page, > > + * but did not account for the compound, sequence, stateid, and > > + * filehandle encoded here. If the variable-length encode overflows t= he > > + * backchannel send buffer, roll back to before the operation so that= a > > + * truncated CB_NOTIFY is never placed on the wire. > > */ > > - xdrgen_encode_CB_NOTIFY4args(xdr, &args); > > + start =3D xdr_stream_pos(xdr); > > + > > + p =3D xdr_reserve_space(xdr, 4); > > + if (!p) > > + goto out_err; > > + *p =3D cpu_to_be32(OP_CB_NOTIFY); >=20 > Please use xdr_stream_encode_u32 for this purpose. >=20 Ok >=20 > > + > > + args.cna_stateid.seqid =3D dp->dl_stid.sc_stateid.si_generation; > > + memcpy(&args.cna_stateid.other, &dp->dl_stid.sc_stateid.si_opaque, > > + ARRAY_SIZE(args.cna_stateid.other)); > > + args.cna_fh.len =3D dp->dl_stid.sc_file->fi_fhandle.fh_size; > > + args.cna_fh.data =3D dp->dl_stid.sc_file->fi_fhandle.fh_raw; > > + args.cna_changes.count =3D ncn->ncn_nf_cnt; > > + args.cna_changes.element =3D ncn->ncn_nf; > > + if (!xdrgen_encode_CB_NOTIFY4args(xdr, &args)) > > + goto out_err; > >=20 > > hdr.nops++; > > encode_cb_nops(&hdr); > > + return; > > + > > +out_err: > > + /* > > + * Drop the CB_NOTIFY op and emit a valid CB_SEQUENCE-only compound s= o > > + * the client still advances its slot. Flag the failure so the done > > + * handler recalls the delegation and the missed notification is not > > + * silently lost. The flag is written here in the transmit path and r= ead > > + * in the done handler; the two are serialized phases of the same > > + * rpc_task, so no additional barrier is needed. > > + */ > > + ncn->ncn_encode_err =3D true; >=20 > This flag is zeroed only once, at allocation time in alloc_init_dir_deleg= (). > It is never cleared in nfsd4_cb_notify_prepare(). >=20 > Since nfsd4_cb_notify_release() can requeue the callback (via > nfsd4_run_cb_notify) when events arrive while a callback is in flight, > ->prepare may encode cleanly and return true, but nfsd4_cb_notify_done() > still observes the stale ncn_encode_err =3D=3D true and calls > nfsd_break_one_deleg() -- discarding a good notification and recalling > the delegation unnecessarily. >=20 Ok, so we need to reset this in ->prepare. >=20 > > + xdr_truncate_encode(xdr, start); > > + encode_cb_nops(&hdr); > > } > >=20 > > static int nfs4_xdr_dec_cb_notify(struct rpc_rqst *rqstp, >=20 > > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c > > index 0a15d7f3b543..513cbc1a583f 100644 > > --- a/fs/nfsd/nfs4state.c > > +++ b/fs/nfsd/nfs4state.c >=20 > > @@ -3471,19 +3472,146 @@ nfsd4_cb_getattr_release(struct nfsd4_callback= *cb) > > nfs4_put_stid(&dp->dl_stid); > > } > >=20 > > +static void nfsd_break_one_deleg(struct nfs4_delegation *dp) > > +{ > > + bool queued; > > + > > + if (test_and_set_bit(NFSD4_CALLBACK_RUNNING, &dp->dl_recall.cb_flags)= ) > > + return; > > + > > + /* > > + * We're assuming the state code never drops its reference > > + * without first removing the lease. Since we're in this lease > > + * callback (and since the lease code is serialized by the > > + * flc_lock) we know the server hasn't removed the lease yet, and > > + * we know it's safe to take a reference. > > + */ > > + refcount_inc(&dp->dl_stid.sc_count); > > + queued =3D nfsd4_run_cb(&dp->dl_recall); > > + WARN_ON_ONCE(!queued); > > + if (!queued) { > > + refcount_dec(&dp->dl_stid.sc_count); > > + clear_bit(NFSD4_CALLBACK_RUNNING, &dp->dl_recall.cb_flags); > > + } > > +} >=20 > nfsd_break_one_deleg() does an unconditional > refcount_inc(&dp->dl_stid.sc_count), and its comment justifies this > with "the lease code is serialized by the flc_lock." That invariant > holds when called from nfsd_break_deleg_cb() under flc_lock, but > nfsd4_cb_notify_prepare() runs on a workqueue WITHOUT flc_lock. Its > out_recall: path calls nfsd_break_one_deleg(dp) > directly. The delegation can be concurrently destroyed with sc_count > already at zero, making this an inc-from-zero. >=20 > The dispatch path nfsd4_run_cb_notify already does this correctly with > refcount_inc_not_zero. The out_recall path needs the same guard (skip > the recall / bail if the refcount is already zero). >=20 > I notice that the last unapplied patch ("nfsd: add > support to CB_NOTIFY for dir attribute changes") rewrites the guard > "if (count > NOTIFY4_EVENT_QUEUE_SIZE)" into "if (count > limit)" with > limit =3D NOTIFY4_EVENT_QUEUE_SIZE - 1 when NOTIFY4_CHANGE_DIR_ATTRS is > requested. That turns the previously-dead overflow branch into a live, > routine path to out_recall, which adds another normal-operation route > into this unlocked recall. >=20 This wart has been there a long time, and we just papered over it with the lock. I think we need to do a refcount_inc_not_zero() in nfsd_break_one_deleg() and just return without queuing the callback if it's already at 0. That means that the recall is racing with the lease teardown, so I think the right thing to do is to not send the recall in that case. --=20 Jeff Layton