From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=91.218.175.53 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793362487; b=a/hRb3BYfL73QrSe1ipjXscIOFzR55TEa9DzeG40wpFavfbmRz0shUrB89qdSs8RLWCG RhMuGDoDXSDMoM2lT8+aQuWFfyVo3BijZH/RgIVqDz4cFv3m/Oq26pbYVZP8sCxShE9rn 5q+QODOGeOne31kfqT66Rku+5ZhiQA2k0X32BeGI8xGMMimxvobcPLu1RfoRNQLt9flFd Yrw4hAO5nan+0FS1njMJUat84NSPNQu5wIX4EHM/GajMoGBaAR24LNkCvR3vkwG6hQuX4 fW78ES1bR7G+NoJFUDCPc1ifI7LTWaKaDDbNe15nqPCmZxIIaRAd/lob3sFfIGYXOgQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793362487; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:MIME-Version:Date:Content-Type: Content-Transfer-Encoding:From:Message-ID:TLS-Required:Subject:To:Cc: In-Reply-To:References; bh=h2ip5SvFQXMjskOPscXy3MGP8bE0cs7x1URhQqE3CrM=; b=s9D6+Zq6M+y77oyVDhiOxlSzHERsr5O3aZOyxXnuV5ZZyKinGJjZzcSBvemYXIgcVw3T liGlSm2sgkQLmgtPMC34ITulCpeqhVDYI0z5gqVWn1tUmtMXa7hj+ANzBC5mNCPlbrM+V BswmpwmcTi6TYkAynvAxtoKrnkCot0nrkvUUlfAEp+laThJnIOc5z4KQY9REtFhZcOHd/ dWvadaEZDtN7drBGGd6BIpxScJGS3Vm9oxk0JtaP8C7ufd/eIhvszcNSAulmQmzGAhSCb 2XgEl1wIgVDrV9Vzgi6vug/6E5OvtM6ehaHqLLbkoq2PTM03pdgrortEdY1ABSqPZZw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=q98j0faV; arc=none smtp.remote-ip=91.218.175.53 Received: from mta0.migadu.com (out-53.mta0.migadu.com [91.218.175.53]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5DACA606A338 for ; Fri, 30 Oct 2026 12:14:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 5DACA606A338 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=q98j0faV X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=HCRBN2Dk48Rcr6GaXJ+oqaIPUyAM1rumz9TPvTLc5b8=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793362484; v=1; x=1793967284; b=q98j0faVFE3L4eZwCTVkdjEkvxFeGPMpErXgdQ/V4ut1+C47ljzXQwzS8NjA4boc9aFAH6JI MQPIYDCAmts/RzJwaLm+DbhxU+cSRSc4nGYfEbWl1fqAhBK0RgoIxbDBOvG9nK5GuB6VrzJEfoG p5HzlaW67kKbQv9P1HGFCxfQ= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id e7652bde6c35a393; Fri, 30 Oct 2026 12:14:44 +0000 X-Mizu-Trace-ID: e7652bde6c35a393 X-Migadu-Flow: FLOW_OUT 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 Date: Fri, 30 Oct 2026 12:14:43 +0000 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable From: "Zqiang" Message-ID: <746fe313c43392e69e99e4f9e9301abda3800a28@linux.dev> TLS-Required: No Subject: Re: [PATCH v2] rcutorture: Avoid create fwd_prog_tasks for tasks-rude and srcu-atomic To: paulmck@kernel.org Cc: frederic@kernel.org, neeraj.upadhyay@kernel.org, joelagnelf@nvidia.com, urezki@gmail.com, boqun@kernel.org, rcu@vger.kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <5cb8b0cb-c7ea-4f2c-a9f9-3ccbab1bddc3@paulmck-laptop> References: <20261023093716.25717-1-qiang.zhang@linux.dev> <5cb8b0cb-c7ea-4f2c-a9f9-3ccbab1bddc3@paulmck-laptop> >=20 >=20On Fri, Oct 23, 2026 at 05:37:16PM +0800, Zqiang wrote: >=20 >=20>=20 >=20> When running the tasks-rude and srcu-atomic tests, the fwd_prog_tas= ks > > kthread is created because the default value of fwd_progress is 1. > > however, the two RCU flavors not support ->call(): > >=20=20 >=20> 1. tasks-rude: commit b428a9de9bba ("rcutorture: Stop testing RCU = Tasks > > Rude asynchronous APIs") removed .call and .cb_barrier from tasks-ru= de, > > but left the .cbflood_max =3D 50000. > >=20=20 >=20> 2. srcu-atomic: srcu_torture_init_forbidden_apis() sets ->call to = NULL > > for SRCU_READ_FLAVOR_ATOMIC runs, but leaves ->cbflood_max untouched= . > >=20=20 >=20> In both cases, the non-zero ->cbflood_max fools the check above in= to > > creating the fwd_prog_tasks kthreads, even though those kthreads can= not > > possibly carry out any forward-progress test: > >=20=20 >=20> 1. The rcu_torture_fwd_prog_cr() returns immediately due to cur_op= s->call > > is NULL: > >=20=20 >=20> [ 68.022674] rcu_torture_fwd_prog_cr: No ->call(), so no forward-p= rogress test 0 > > [ 129.462046] rcu_torture_fwd_prog_cr: No ->call(), so no forward-pr= ogress test 0 > > [ 190.902123] rcu_torture_fwd_prog_cr: No ->call(), so no forward-pr= ogress test 0 > > [ 252.343809] rcu_torture_fwd_prog_cr: No ->call(), so no forward-pr= ogress test 0 > >=20=20 >=20> 2. The rcu_torture_fwd_prog_nr() is never even invoked, because it= s caller > > requires cur_ops->stall_dur, and neither tasks-rude nor srcu-atomic > > provide ->stall_dur (only rcu_ops does). > >=20=20 >=20> Therefore, creating fwd_prog_tasks kthreads is pointless, this com= mit adds > > ->call and ->cb_barrier to the forward-progress check, rejecting fla= vors > > that lack the cbflood_max set and a positive ->stall_dur. > >=20=20 >=20> simple verification output: > >=20=20 >=20> [ 3.062959][ T1] srcu-torture: rcu_torture_fwd_prog_init: Disabled= , unsupported by RCU flavor under test > > [ 2.922323][ T1] tasks-rude-torture: rcu_torture_fwd_prog_init: Disa= bled, unsupported by RCU flavor under test > >=20=20 >=20> Suggested-by: Joel Fernandes =20 >=20> Signed-off-by: Zqiang > >=20 >=20Reviewed-by: Paul E. McKenney >=20 >=20It would nevertheless be good to run tests demonstrating that > forward-progress testing happens and does not happen on the same > rcu_torture_ops structures as before. Just in case I lost my > way through that boolean expression. ;-) Ok, I see. thanks Paul ;-) . >=20 >=20>=20 >=20> --- > > kernel/rcu/rcutorture.c | 5 ++--- > > 1 file changed, 2 insertions(+), 3 deletions(-) > >=20=20 >=20> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c > > index 968343be4e0d..92ff197f4789 100644 > > --- a/kernel/rcu/rcutorture.c > > +++ b/kernel/rcu/rcutorture.c > > @@ -4007,9 +4007,8 @@ static int __init rcu_torture_fwd_prog_init(vo= id) > > } else if (fwd_progress < 0) { > > fwd_progress =3D nr_cpu_ids; > > } > > - if ((!cur_ops->sync && !cur_ops->call) || > > - (!cur_ops->cbflood_max && (!cur_ops->stall_dur || cur_ops->stall_d= ur() <=3D 0)) || > > - cur_ops =3D=3D &rcu_busted_ops) { > > + if (!cur_ops->sync || ((!cur_ops->call || !cur_ops->cb_barrier || = !cur_ops->cbflood_max) && > > + (!cur_ops->stall_dur || cur_ops->stall_dur() <=3D 0))) { > > VERBOSE_TOROUT_STRING("rcu_torture_fwd_prog_init: Disabled, unsuppor= ted by RCU flavor under test"); > > fwd_progress =3D 0; > > return 0; > > --=20 >=20> 2.17.1 > > >