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 8B9CB52F286; Tue, 22 Sep 2026 10:18:32 +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=1790072313; cv=none; b=FHzvnAOFczG40DCMzzCn29pej2QE8hKHLOVL2KDy/eLsvkNXQ+gY2pzXc/HISASsBiCGB2re1QbOirQkTteh5rNHhIYPItvV912NI8qhET8GZlDdnUnvf/nDpHE7hH1QnrS7h8y+SVfoc48qSFdalR+Z7G9uQgKTYRd5YdrZ1fs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790072313; c=relaxed/simple; bh=cIW1HGIrp5Cm5u63WVdN7v+5LS1NWXLxArpJmOZne50=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=FQ62GoqLeu8/BqRlD1R/gqbzU3PpHf73OXtXVdVat1KcD04meJIlapK5OxeZvcMn95BuE5nFqDRWw+RxF+S6tokMMfmuTskoAGEBz4kajdVBrhcyF2ltlGzYrlgcO59imR6Wb+imVb2nrn7jSqSnfXVLXp5ddm2vnURmVInYg8o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=n8HgnaPn; 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="n8HgnaPn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 76DFD1F000FF; Tue, 22 Sep 2026 10:18:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790072312; bh=cZKkPK68VyCM3iNaYcjV1nG7EQlHZxNltaoWrb9ogYw=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=n8HgnaPnrL8V1ExtlkbvoME2eaYn/7wXh7Ke5fOaglm0/AnZ74wcHr4KxkXE9sXW/ eNkJnIf7t8ik1HFVPRQkmGsGF6uu7/n9PK62KKBEN6gkmmp6UMjsbt4z7PoMvyxw3A uz2wqMfgwa5r+Ewf2j2Tq6Nam3WIdlkCe9+8q9ERNShoeu9XQiB7r+KmHLU7ZPSbPe s6Jc9PESIj2mRHYLfniBexT3zajYVX9lPlLLPGxbuqPvKgJzAwSU5nKrXYR6/Zyj3U tvbztqemL5FjY+SoxYrRQb/5MYLLmmYsKka8WzKLT0l8FsxAvs3CAanb4JtzGdEO8s 5v8RjkqbFIxjw== Message-ID: <40519389abdabce49e87ce1082d5fa3df6cc064d.camel@kernel.org> Subject: Re: [PATCH 5/8] nfsd: give the open file cache its own mutex From: Jeff Layton To: NeilBrown Cc: Chuck Lever , Olga Kornievskaia , Dai Ngo , Tom Talpey , Shuah Khan , linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Date: Tue, 22 Sep 2026 06:18:29 -0400 In-Reply-To: <179005907144.37859.15558964767750002575@noble.neil.brown.name> References: <20260921-nfsd-per-net-mutex-v1-0-4a7287f6504c@kernel.org> <20260921-nfsd-per-net-mutex-v1-5-4a7287f6504c@kernel.org> <179005907144.37859.15558964767750002575@noble.neil.brown.name> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw 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Evolution 3.60.2 (3.60.2-2.fc44) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2026-09-22 at 16:37 +1000, NeilBrown wrote: > On Tue, 22 Sep 2026, Jeff Layton wrote: > > nfsd_global_mutex still serializes file cache flushes against server > > start/stop in unrelated namespaces. nfsd_file_cache_purge() is reached = from > > expkey_flush() on every "exportfs -f", which makes it the only frequent > > taker of the global lock -- and it has nothing to do with nfsd_users or= the > > NFSv4 global tables it would be waiting on. > >=20 > > Move NFSD_FILE_CACHE_UP and the objects it covers (rhltable, LRU, slabs= , > > shrinker, fsnotify groups) onto a nfsd_file_cache_mutex private to > > filecache.c. nfsd_file_cache_init() and nfsd_file_cache_shutdown() take= it > > themselves rather than asserting the caller holds the global one, so > > nfssvc.c no longer needs to know how the cache locks itself. > >=20 > > nfsd_global_mutex is left holding only nfsd_users, the notifier count a= nd > > user_recovery_dirname, all of which are touched solely on server > > start/stop. > >=20 > > Ordering is nn->nfsd_mutex outside nfsd_global_mutex outside > > nfsd_file_cache_mutex. The cache mutex is reached three ways, all > > consistent with that: from nfsd_startup_generic()/nfsd_shutdown_generic= () > > under the global mutex, from nfsd_shutdown_net() under nn->nfsd_mutex, = and > > bare from expkey_flush() and the filecache stats file. Nothing called w= ith > > the cache mutex held takes either of the others. > >=20 > > Assisted-by: LLM > > Signed-off-by: Jeff Layton > > --- > > fs/nfsd/filecache.c | 39 ++++++++++++++++++++++++++++----------- > > fs/nfsd/nfssvc.c | 9 +++++---- > > 2 files changed, 33 insertions(+), 15 deletions(-) > >=20 > > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c > > index 501772bc8f8d..179362e5394b 100644 > > --- a/fs/nfsd/filecache.c > > +++ b/fs/nfsd/filecache.c > > @@ -67,6 +67,17 @@ > > */ > > static DEFINE_SPINLOCK(nfsd_gc_lock); > > =20 > > +/* > > + * Guards NFSD_FILE_CACHE_UP and the host-wide objects it covers: the > > + * rhltable, the LRU, the slabs, the shrinker and the fsnotify groups. > > + * Held across cache bring-up and teardown, and by readers and walkers > > + * that need the cache to stay up for the duration (->cache_purge, the > > + * stats file). > > + * > > + * Nests inside nfsd_global_mutex and inside nn->nfsd_mutex. > > + */ > > +static DEFINE_MUTEX(nfsd_file_cache_mutex); > > + > > static DEFINE_PER_CPU(unsigned long, nfsd_file_cache_hits); > > static DEFINE_PER_CPU(unsigned long, nfsd_file_acquisitions); > > static DEFINE_PER_CPU(unsigned long, nfsd_file_allocations); > > @@ -869,9 +880,11 @@ nfsd_file_cache_init(void) > > { > > int ret; > > =20 > > - lockdep_assert_held(&nfsd_global_mutex); > > - if (test_and_set_bit(NFSD_FILE_CACHE_UP, &nfsd_file_flags) =3D=3D 1) > > + mutex_lock(&nfsd_file_cache_mutex); >=20 > What would you think of making this >=20 > guard(mutex)(&nfsd_file_cache_mutex); >=20 > so you don't need to make other changes in this function?? >=20 >=20 Sounds good. I'll do that. Thanks! --=20 Jeff Layton