From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 51C1A1917FA for ; Tue, 10 Sep 2024 12:52:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725972726; cv=none; b=q1fThDkcrOw1exriiE64KtZ9Ns0ua0JZQDAXB6OzzOhFd+6c7vELYhIB09DVPd1DgVuAXXpOCdEXXuQBhHyOfDfCsiZ3oKN5jOcWzJRvq/9Y4VLnf6+LkHonQKymzdNzHh7V0/FzgWGFc2MHxp/C4wHNCKmU49PPfzlVQmUXCfI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725972726; c=relaxed/simple; bh=jPKCZgr92hVekWicb7VW8tZKTVP+SkPDo/iNZFbGal8=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=LTA2oBzpa7SMacZKQ9qjt+RS/zXs/AtSt7WH3eIZllMAypd+4d1UW6Xmmm/eEj+SR8+Nh8lxKdtQaTWdIpyxLRKGgaMzD7G4uS7x/Xekprn3yD9wFO8cymtsZqGUwUBJsDWyBk5qIoapuJ0MbmUb2hD1ETTyPCnKwbGQNkI07K0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=rvLSN6hB; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="rvLSN6hB" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4B53EC4CEC6; Tue, 10 Sep 2024 12:52:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1725972725; bh=jPKCZgr92hVekWicb7VW8tZKTVP+SkPDo/iNZFbGal8=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=rvLSN6hBE5CxQLsZUDwaVWZc5bub1zK2Xa0XOytwMelsmunq3Tjxgcj+BA/ngtCLc udzx4ijRlbP4nx0yLrSbyKQs9QapIUni+IXguUAqrtxeyOSJttdJtxMvlUEeHLcXKl vIOBIs8jiYq1y7O5hpMxMpLCde6CVknDM5jDTI0t/uSXHAHW71porppezXuHe6qenA /fceHlzOgmk92FCCC0VfVkvRbPWMFGALhlUyVUAHm42GjNo1AkBEkpV/zUo01DQRRe jwJZL3jU+YGX20ZIqN473e9tZ+e467w4qV4LSmtpUQMPyaBrigxXpUeeuZkfS7n55S DbaFra+GEZprA== Message-ID: <8e02bafe8027b060b38d38ebbd3092d2beb35206.camel@kernel.org> Subject: Re: [PATCH] nfsd: fix delegation_blocked() to block correctly for at least 30 seconds From: Jeff Layton To: Tom Talpey , Olga Kornievskaia , Chuck Lever Cc: NeilBrown , Dai Ngo , linux-nfs@vger.kernel.org Date: Tue, 10 Sep 2024 08:52:04 -0400 In-Reply-To: <727023c4-416d-43ba-a82a-3fbd0a831f49@talpey.com> References: <172585839640.4433.13337900639103448371@noble.neil.brown.name> <727023c4-416d-43ba-a82a-3fbd0a831f49@talpey.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV 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Tue, 2024-09-10 at 08:32 -0400, Tom Talpey wrote: > On 9/9/2024 11:02 AM, Olga Kornievskaia wrote: > > On Mon, Sep 9, 2024 at 10:38=E2=80=AFAM Chuck Lever wrote: > > >=20 > > > On Mon, Sep 09, 2024 at 10:17:42AM -0400, Olga Kornievskaia wrote: > > > > On Mon, Sep 9, 2024 at 8:24=E2=80=AFAM Jeff Layton wrote: > > > > >=20 > > > > > On Mon, 2024-09-09 at 15:06 +1000, NeilBrown wrote: > > > > > > The pair of bloom filtered used by delegation_blocked() was int= ended to > > > > > > block delegations on given filehandles for between 30 and 60 se= conds. A > > > > > > new filehandle would be recorded in the "new" bit set. That wo= uld then > > > > > > be switch to the "old" bit set between 0 and 30 seconds later, = and it > > > > > > would remain as the "old" bit set for 30 seconds. > > > > > >=20 > > > > >=20 > > > > > Since we're on the subject... > > > > >=20 > > > > > 60s seems like an awfully long time to block delegations on an in= ode. > > > > > Recalls generally don't take more than a few seconds when things = are > > > > > functioning properly. > > > > >=20 > > > > > Should we swap the bloom filters more often? > > > >=20 > > > > I was also thinking that perhaps we can do 15-30s perhaps? Another > > > > thought was should this be a configurable value (with some > > > > non-negotiable min and max)? > > >=20 > > > If it needs to be configurable, then we haven't done our jobs as > > > system architects. Temporarily blocking delegation ought to be > > > effective without human intervention IMHO. > > >=20 > > > At least let's get some specific usage scenarios that demonstrate a > > > palpable need for enabling an admin to adjust this behavior (ie, a > > > need that is not simply an implementation bug), then design for > > > those specific cases. > > >=20 > > > Does NFSD have metrics in this area, for example? > > >=20 > > > Generally speaking, though, I'm not opposed to finessing the behavior > > > of the Bloom filter. I'd like to apply the patch below for v6.12, > >=20 > > 100% agreed that we need this patch to go in now. The configuration > > was just a thought for after which I should have stated explicitly. I > > guess I'm not a big fan of hard coded numbers in the code and naively > > thinking that it's always better to have a config over a hardcoded > > value. >=20 > No constant is ever correct in networking, especially timeouts. So yes, > it should be adjustable. But even then, choosing a number here is > fundamentally difficult. >=20 > Delegations can block for perfectly valid long periods, right? Say it > takes a long time to flush a write delegation, or if the network is > partitioned to the (other) client being recalled. 30 seconds to data > corruption is quite the guillotine. >=20 I don't think this is danger of data corruption here. The bloom filter is there to keep the server from handing out a new delegation too quickly after having to recall one. Allowing no delegations for 30-60s seems a bit too cautious, IMO.=20 Ideally it seems like we'd want this to be some function of the delay between the server issuing the CB_RECALL, and the client doing the DELEGRETURN. That value is obviously highly variable, but it would be an interesting statistic to collect, and might help inform what the bloom filter delay should be. > > > preserving the Cc: stable, but handle the behavioral finessing via > > > a subsequent patch targeting v6.13 so that can be appropriately > > > reviewed and tested. Ja? > > >=20 > > > BTW, nice catch! > > >=20 > > >=20 > > > > > > Unfortunately the code intended to clear the old bit set once i= t reached > > > > > > 30 seconds old, preparing it to be the next new bit set, instea= d cleared > > > > > > the *new* bit set before switching it to be the old bit set. T= his means > > > > > > that the "old" bit set is always empty and delegations are bloc= ked > > > > > > between 0 and 30 seconds. > > > > > >=20 > > > > > > This patch updates bd->new before clearing the set with that in= dex, > > > > > > instead of afterwards. > > > > > >=20 > > > > > > Reported-by: Olga Kornievskaia > > > > > > Cc: stable@vger.kernel.org > > > > > > Fixes: 6282cd565553 ("NFSD: Don't hand out delegations for 30 s= econds after recalling them.") > > > > > > Signed-off-by: NeilBrown > > > > > > --- > > > > > > fs/nfsd/nfs4state.c | 5 +++-- > > > > > > 1 file changed, 3 insertions(+), 2 deletions(-) > > > > > >=20 > > > > > > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c > > > > > > index 4313addbe756..6f18c1a7af2e 100644 > > > > > > --- a/fs/nfsd/nfs4state.c > > > > > > +++ b/fs/nfsd/nfs4state.c > > > > > > @@ -1078,7 +1078,8 @@ static void nfs4_free_deleg(struct nfs4_s= tid *stid) > > > > > > * When a delegation is recalled, the filehandle is stored in= the "new" > > > > > > * filter. > > > > > > * Every 30 seconds we swap the filters and clear the "new" o= ne, > > > > > > - * unless both are empty of course. > > > > > > + * unless both are empty of course. This results in delegatio= ns for a > > > > > > + * given filehandle being blocked for between 30 and 60 second= s. > > > > > > * > > > > > > * Each filter is 256 bits. We hash the filehandle to 32bit = and use the > > > > > > * low 3 bytes as hash-table indices. > > > > > > @@ -1107,9 +1108,9 @@ static int delegation_blocked(struct knfs= d_fh *fh) > > > > > > if (ktime_get_seconds() - bd->swap_time > 30) { > > > > > > bd->entries -=3D bd->old_entries; > > > > > > bd->old_entries =3D bd->entries; > > > > > > + bd->new =3D 1-bd->new; > > > > > > memset(bd->set[bd->new], 0, > > > > > > sizeof(bd->set[0])); > > > > > > - bd->new =3D 1-bd->new; > > > > > > bd->swap_time =3D ktime_get_seconds(); > > > > > > } > > > > > > spin_unlock(&blocked_delegations_lock); > > > > >=20 > > > > > -- > > > > > Jeff Layton > > > > >=20 > > > >=20 > > >=20 > > > -- > > > Chuck Lever > > >=20 > >=20 > >=20 >=20 --=20 Jeff Layton