From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793705886; b=yB01VcKRxIRRG+uDuOhCbmTmxe2x0xOVFSFSPVgkTBgpuWhqqRkJLOTsF7hDMuhQLs9O 6WnDPvWrwcNUb/70MfhKzQiT0tMIWh77iX//nET5dh6J2/QO3zhYA03ISny2eLzIN8OXx jktSM2uwTWbYoJnBIQ45tTBf6CLlr2rkX5d3k3V6UhIeIqYoXnX+D28Xg0WX+PzpGBmdJ rVBHjEDJqq1n6S5VnHtGiu7ApL43IcO1SmQnM3S1g2OrtMNjE0WESVA0maYtUVIVWbH1m uB/TKJiiacK0iwAwqxN36K5LVUNr/qkvRlTt8MMoSgY6VZ5K7Kmm1lPCf5xa4WIMpcQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793705886; h=Received:DKIM-Signature:Message-ID:Subject:From:To:Cc:Date: In-Reply-To:References:Autocrypt:Content-Type: Content-Transfer-Encoding:User-Agent:MIME-Version; bh=jV8hJnCNXZ3oV7ew7jsIZgzVSy3GGv0vDpJ2ca3lNHg=; b=dp+GnIhibvybFFYEp6GvZzuogYJpA4dc299cpwI3kbCIVtFyYBpzG0eWxwAiuEOdNc1l lY1JUROv1CMSLwLIuu130/n2lHDSagflCnwI+hxCbfao0KC9xaZFt9onpTz9413+MuTtZ K/3KblllefzMLmcKDHPQv2KkzY/N0ki28phqzwrNT3lI0re40ZMqMvZdeyFRExM4xDMdi qHb73w2zfWJqkaUVgO53cAQnefC9S9fxH6l7yoFL8yvWB9ykf3ZHGNjiGXgVBC2Bvm0Vn pnfvBtSeQJT5R9mhdYlADWSKNttLiemwf9iCtV0iwJ3/CVNoPi9t+fSGUSW8beh1Ljg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Qou8YGec; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AD5A9606A33B; Tue, 3 Nov 2026 11:38:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Qou8YGec Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0C19E1F00919; Tue, 3 Nov 2026 11:38:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793705885; bh=jV8hJnCNXZ3oV7ew7jsIZgzVSy3GGv0vDpJ2ca3lNHg=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=Qou8YGecM5FCM0oNyM8ogjT5lIJ8FRRRDULeERoUyXtMXAgApaPOIHD4veytEbMpj 2DtkM6c6QQGhn2NoNmPtaynqyjykH4RZICs+yzlycDzXwMClioxEMJgCyaF74BAmT1 6H/ExjAgai0DjlnVqILFWp6oGFNTTTWk4+vQrA7JVWUi+BUbUxzIxuqS7oPBOj6FFs tj3x17D7SoqhxN3L1GVaQS2X7MncZ5OTZP3TsLw/LVdRQmf0aB5x7K82/eQQ2e4+iV qqODP/GfXgOY90M5aWQYyk369O0ERbrOKKRtmPqVHNfQWKG+9uKGKSM6aYTrqOBYM0 Do20RI1ktnDYg== Message-ID: Subject: Re: [PATCH v2] sunrpc: fix lost wakeups when stopping service threads From: Jeff Layton To: Kal Cutter Conley , Trond Myklebust , Anna Schumaker , Chuck Lever , NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman Cc: linux-nfs@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Date: Tue, 03 Nov 2026 06:38:02 -0500 In-Reply-To: <20261102225358.414367-1-kalcutterc@nvidia.com> References: <20261030130629.103716-1-kalcutterc@nvidia.com> <20261102225358.414367-1-kalcutterc@nvidia.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn VluJH0/RcxEeFbnSaswVChNSGa7mXJrTR22lRL6ZPjdMgS2Km90haWPRc8Wolcz07Y2se0xpGVLEQ 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CHqumUHRry+RF0lH00clzX/W8OrQJZtoBPXv9ahka/Vp7kEulcBJr1cH5Wz/WprhsIM7U9pse1f1g Yy9YbXtWctUz8uvDR7shsQxAhX3qO7DilMtuGo1v97I/Kx4gXQ52syh/w6EBny71CZrOgD6kJwPVV AaM1LRC28muq91WCFhs/nzHozpbzcheyGtMUI2Ao4K6mnY+3zIuXPygZMFr9KXE6fF7HzKxKuZMJO aEZCiDOq0anx6FmOzs5E6Jqdpo/mtI8beK+BE7Va6ni7YrQlnT0i3vaTVMTiCThbqsB20VrbMjlhp f8lfK1XVNbRq/R7GZ9zHESlsa35ha60yd/j3pu5hT2xyy8krV8vGhHvnJ1XRMJBAB/UYb6FyC7S+m QZIQXVeAA+smfTT0tDrisj1U5x6ZB9b3nBg65kc= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.2 (3.60.2-3.fc44) X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 On Mon, 2026-11-02 at 23:53 +0100, Kal Cutter Conley wrote: > Stopping NFS can leave rpc.nfsd 0 in an uninterruptible wait with > this stack: >=20 > svc_stop_kthreads [sunrpc] > svc_set_num_threads [sunrpc] > nfsd_svc [nfsd] > write_threads [nfsd] > nfsctl_transaction_write [nfsd] >=20 > SP_NEED_VICTIM and SP_VICTIM_REMAINS remain set while all remaining > nfsd threads sleep in svc_recv() and none has RQ_VICTIM set. >=20 > The stop request is published with unordered set_bit() operations. > svc_pool_wake_idle_thread() checks the idle list and task state before > calling wake_up_process(). If it sees an empty list or TASK_RUNNING, > it skips the wakeup and its memory barrier. The requester can therefore > miss a sleeping worker while that worker misses the stop request. >=20 > Use smp_mb__after_atomic() after the flag updates in > svc_stop_kthreads() and svc_wake_up() to order work publication before > both lockless checks, even when no wakeup occurs. Pair with > set_current_state() and llist_add() in svc_thread_wait_for_work(), so > the worker observes the pending work or the requester observes the > idle worker and wakes it. >=20 > Fixes: 60749cbe3d8a ("sunrpc: change sp_nrthreads from atomic_t to unsign= ed int.") > Signed-off-by: Kal Cutter Conley > --- > Changes in v2: > - Move the barrier into svc_stop_kthreads() and svc_wake_up(), using > smp_mb__after_atomic(). This avoids adding a redundant barrier on the > transport enqueue path. >=20 > v1: https://lore.kernel.org/r/20261030130629.103716-1-kalcutterc@nvidia.c= om >=20 > net/sunrpc/svc.c | 7 +++++++ > net/sunrpc/svc_xprt.c | 5 +++++ > 2 files changed, 12 insertions(+) >=20 > diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c > index af8d87c1de83..76232774646c 100644 > --- a/net/sunrpc/svc.c > +++ b/net/sunrpc/svc.c > @@ -29,6 +29,8 @@ > #include > #include > =20 > +#include > + As Neil said, this is probably not needed. > #include > =20 > #include "fail.h" > @@ -784,6 +786,11 @@ svc_stop_kthreads(struct svc_serv *serv, struct svc_= pool *pool, int nrservs) > do { > set_bit(SP_VICTIM_REMAINS, &pool->sp_flags); > set_bit(SP_NEED_VICTIM, &pool->sp_flags); > + /* > + * Order flag updates before the idle list and task state checks. > + * Pairs with the barriers in svc_thread_wait_for_work(). > + */ > + smp_mb__after_atomic(); > svc_pool_wake_idle_thread(pool); > wait_on_bit(&pool->sp_flags, SP_VICTIM_REMAINS, TASK_IDLE); > nrservs++; > diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c > index 076c624fe675..868e3da57b6c 100644 > --- a/net/sunrpc/svc_xprt.c > +++ b/net/sunrpc/svc_xprt.c > @@ -632,6 +632,11 @@ void svc_wake_up(struct svc_serv *serv) > struct svc_pool *pool =3D &serv->sv_pools[0]; > =20 > set_bit(SP_TASK_PENDING, &pool->sp_flags); > + /* > + * Order flag updates before the idle list and task state checks. > + * Pairs with the barriers in svc_thread_wait_for_work(). > + */ > + smp_mb__after_atomic(); > svc_pool_wake_idle_thread(pool); > } > EXPORT_SYMBOL_GPL(svc_wake_up); >=20 > base-commit: 2d3259f652bb0f1d137ccabecac6763da05064ec Reviewed-by: Jeff Layton