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 6308D40F755; Mon, 24 Aug 2026 12:00:07 +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=1787572808; cv=none; b=XEtC3RZ6ZZ6g+tuu5vkCNtQjx5L5290YIU9SqepaQuBfa4y860ljt/gu8I9KNjrf21e9i/zCH38fBgOYbWE5edrMt0EUFDR1ON7sl9l+5V8kULV2Wi2GI90nfKnJrHgKN4fiLVevImKTWcxqQ38WrQbBqKr7OxWxW/hpVYTUNQU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787572808; c=relaxed/simple; bh=XO409K0StwpLQ51ttUnysXq9fibcVbJfjW6VngM7GzU=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=NmTlvfJY41+MkzOnnTp3WcfGWPNVjL/cbbgXhf5Uhz1zJU7IFHw+EnKIiUTX7JWlk/NgaBP3zNmyTMTHX7YqzdEjQ6/PaPDYTc+kJCkf6rEk+utm5P9Bemn5Q2jaRY18TYdFhx+ZHEVxPEG6hGKSds0tLicAKG0Ptsbr/cmIXco= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VgLKseqW; 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="VgLKseqW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1B5B31F000E9; Mon, 24 Aug 2026 12:00:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787572807; bh=XO409K0StwpLQ51ttUnysXq9fibcVbJfjW6VngM7GzU=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=VgLKseqWQpqDndGPbJJhdF6YhVpH5QytuXmaGdh/SRH+MRo2X3PIBMOCBhOuc4/37 HnpiQuULhmzGxLyNNruSXMuKxR5yBc8ooVzMwQStM6EcOWjIswJsI2J0sLhVGMFcfp 0vF+ypPMcHJJ9TMTAkvm3mgrwqgY6ZB51FbWhdsL4rS0srugTuJGT1fq2P4wqnAQA5 OAhsu992GxvZYcWJicn/y35giqb4Rufr1BMfnD1YjLnMxW3SgzcZpslAOX5ULCHD1F e3tfhbzzxttWyDM50BrIAk+eu6MrZW3ee6GQkqPntWqG4VzZSPrzgjwRdCwg3bhVSK HKRWqiiLNPIhA== Message-ID: <15f03f6f3c8a3b0f1d68fcf376fb082e1b4dbc5d.camel@kernel.org> Subject: Re: [PATCH] nfsd: prevent hung task in nfsd_nl_listener_set_doit() From: Jeff Layton To: Slawomir Stepien Cc: syzbot , syzkaller-bugs@googlegroups.com, Chuck Lever , linux-nfs@vger.kernel.org, Lorenzo Bianconi , Dai.Ngo@oracle.com, linux-kernel@vger.kernel.org, neil@brown.name, okorniev@redhat.com, syzbot@lists.linux.dev, tom@talpey.com Date: Mon, 24 Aug 2026 08:00:04 -0400 In-Reply-To: References: <4601ffd5-c662-4ab1-ab2f-50a67a0a990e@mail.kernel.org> <699bacb503758fbe2ebf01f3e8aca95e3eee4128.camel@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv 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linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Sun, 2026-08-23 at 22:27 +0200, Slawomir Stepien wrote: > On sie 20, 2026 07:37, Jeff Layton wrote: > > On Thu, 2026-08-20 at 06:55 +0000, syzbot wrote: > > > From: Slawomir Stepien > > >=20 > > > In nfsd_nl_listener_set_doit(), the kernel iterates over all > > > NFSD_A_SERVER_SOCK_ADDR attributes provided in a netlink message to > > > configure NFS server listeners. There is currently no limit on the nu= mber > > > of attributes a user can send. > > >=20 > > > For each attribute, svc_xprt_create_from_sa() is called, which may > > > synchronously invoke request_module() to load the corresponding trans= port > > > module. If a user provides a large number of invalid transport names, > > > request_module() is called sequentially for each, taking a massive am= ount > > > of time. Since this entire process occurs while holding the global > > > nfsd_mutex, it blocks other tasks attempting to acquire the mutex and > > > triggers a hung task timeout: > > >=20 > >=20 > > My LLM latched onto the same explanation, but the request module > > upcalls are actually quite quick and have some other gates on them that > > make this problem hard to hit in practice. >=20 > Oh, OK. Thanks for clearing that up! >=20 > > The real problem is rpcbind registration, which can be quite slow. The > > fix for that is to make the registration asynchronous, and to not > > trigger errors on rpcbind registration failure. That's a bigger > > project, but let us know if you're interested! >=20 > I think I'm not that good to do it correctly and in some reasonable time.= I might take a 2nd look at > this and understand the root cause (also, based on your comments in your = series) but I think in the > end it might be too hard for me. >=20 Fair enough. It's a non-trivial project, and after some discussion with Chuck, I'm leaning toward moving most of the rpcbind registration into userland. That'll mean having to rev the netlink protocol, etc. Right now, I don't have a timeline for working on this, so we're probably just going to have to suffer with more syzbot reports until that can come to fruition. --=20 Jeff Layton