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 9A2CB25D527 for ; Mon, 6 Apr 2026 14:38:27 +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=1775486307; cv=none; b=f9scAEG0ygO50rM1ORTN3HEXVb1UiUFKTQ8psH+f7jdo68BXWCr9xZNcT5nTdIaLm6eZ88Y/Ou7Gj2/P9Und9JCz0hA9RDqBgJTgvUoY3pBJ/ytSKDttaXo+nzNdl9YXKnxYh9peldJwiCopH3jaF0Mx+OOjf8dfNtsU4RMMmqU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775486307; c=relaxed/simple; bh=kYdaMf7g+ej9zCGEkJzPFJLqh6fd7nGXXBVqnd3fzsk=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=OaZ/iAsdFNdR/fTk+BNDGeZxftfTJRxF47+7efY8ekNbmQDr5sfksXkzmM2cGwWX7epLUAUEXQSzIazkQf8hfYAxcGs0NrPuWk2eHLCB13hUYQdB3BHnkw3kj0j0cxkUzyBVkDM+CtTCRMt8Csq+80KBmiNuPjDDXT88QoJQ6uk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=YDXxEUEC; 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="YDXxEUEC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7766FC4CEF7; Mon, 6 Apr 2026 14:38:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775486307; bh=kYdaMf7g+ej9zCGEkJzPFJLqh6fd7nGXXBVqnd3fzsk=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=YDXxEUECcMbCmElLtllduYXWqn8rKowmpJO/4/LrcZmn/wTkKevG1UIrzJUWYeLBH WISdcnl3TEABVDqoXzZlaRfZGn6zuFEHiHpS/PpQWOI10MeRVImlhpy54uMiGxXME/ qqeqRO7tmMapgwOnJJoat2OmMD+TaomAyUfGsYGsn5zTnE2YiqgppqQglBcXMR+HNn HRq0DOH72B7ga8OH3/0eSnwUir3GT/5wz92t1JaF8pPHyANf0NdjbvcSh3GvF+JC/n bo25O8iOAwJ+i2nMG/v83qJj0UQ1yDpaNVQoaC97hVW4T3lSnoqCuU7qLKP0ajAWhp Vjz6RQatlnX7Q== Message-ID: Subject: Re: [PATCH v2] nfsd: fix file change detection in CB_GETATTR From: Jeff Layton To: Chuck Lever , Scott Mayhew Cc: Chuck Lever , NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey , linux-nfs@vger.kernel.org Date: Mon, 06 Apr 2026 10:38:24 -0400 In-Reply-To: References: <20260404005405.1565136-1-smayhew@redhat.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV 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> On Fri, Apr 3, 2026, at 8:54 PM, Scott Mayhew wrote: >=20 > > > > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c > > > > index fa657badf5f8..53d8e7e7d60b 100644 > > > > --- a/fs/nfsd/nfs4state.c > > > > +++ b/fs/nfsd/nfs4state.c > > >=20 > > > > @@ -9459,17 +9461,18 @@ static int cb_getattr_update_times(struct= =20 > > > > dentry *dentry, struct nfs4_delegation > > > > * caller must put the reference. > > > > */ > > > > __be32 > > > > -nfsd4_deleg_getattr_conflict(struct svc_rqst *rqstp, struct dentry= =20 > > > > *dentry, > > > > - struct nfs4_delegation **pdp) > > > > +nfsd4_deleg_getattr_conflict(struct svc_rqst *rqstp, struct path *= path, > > > > + struct kstat *stat, struct nfs4_delegation **pdp) > > >=20 > > > Passing the kstat struct in saves some stack just as I suggested, > > > but it is an ugly API. The nfsd4_encode_fattr4() call stack is tall, > > > though -- did you happen to measure how deep it gets after this patch > > > is applied? > > >=20 > >=20 > > I tried using the stack tracer: > >=20 > > # echo 1 >/proc/sys/kernel/stack_tracer_enabled > > # echo vfs_getattr >/sys/kernel/debug/tracing/stack_trace_filter > > # cat /sys/kernel/debug/tracing/stack_trace > > Depth Size Location (18 entries) > > ----- ---- -------- > > 0) 1936 48 vfs_getattr+0x9/0x50 > > 1) 1888 552 nfsd4_encode_fattr4+0x1b2/0x7a0 [nfsd] > > 2) 1336 80 nfsd4_encode_entry4_fattr+0xf8/0x210 [nfsd] > > 3) 1256 96 nfsd4_encode_entry4+0x10b/0x2a0 [nfsd] > > 4) 1160 144 nfsd_buffered_readdir+0x139/0x310 [nfsd] > > 5) 1016 80 nfsd_readdir+0x9f/0x180 [nfsd] > > 6) 936 80 nfsd4_encode_readdir+0xdf/0x1e0 [nfsd] > > 7) 856 80 nfsd4_encode_operation+0xcf/0x3d0 [nfsd] > > 8) 776 80 nfsd4_proc_compound+0x1d6/0x7a0 [nfsd] > > 9) 696 80 nfsd_dispatch+0xd9/0x240 [nfsd] > > 10) 616 80 svc_process_common+0x4cb/0x6b0 [sunrpc] > > 11) 536 40 svc_process+0x150/0x240 [sunrpc] > > 12) 496 72 svc_handle_xprt+0x4b0/0x5f0 [sunrpc] > > 13) 424 56 svc_recv+0x1b2/0x3a0 [sunrpc] > > 14) 368 80 nfsd+0x11c/0x3d0 [nfsd] > > 15) 288 56 kthread+0xe3/0x120 > > 16) 232 40 ret_from_fork+0x1a1/0x270 > > 17) 192 192 ret_from_fork_asm+0x1a/0x30 > >=20 > > But that's capturing a vfs_getattr() call from encoding a readdir reply= , > > rather than the vfs_getattr() call I added to nfsd4_deleg_getattr_confl= ict(). > >=20 > > Here's the stack depth for nfsd4_deleg_getattr_conflict(): > >=20 > > # echo nfsd4_deleg_getattr_conflict=20 > > > /sys/kernel/debug/tracing/stack_trace_filter > > # echo 0 >/sys/kernel/debug/tracing/stack_max_size=20 > > # cat /sys/kernel/debug/tracing/stack_trace > > Depth Size Location (14 entries) > > ----- ---- -------- > > 0) 1472 48 nfsd4_deleg_getattr_conflict+0x9/0x410 [nfsd] > > 1) 1424 552 nfsd4_encode_fattr4+0x191/0x7a0 [nfsd] > > 2) 872 16 nfsd4_encode_getattr+0x2c/0x40 [nfsd] > > 3) 856 80 nfsd4_encode_operation+0xcf/0x3d0 [nfsd] > > 4) 776 80 nfsd4_proc_compound+0x1d6/0x7a0 [nfsd] > > 5) 696 80 nfsd_dispatch+0xd9/0x240 [nfsd] > > 6) 616 80 svc_process_common+0x4cb/0x6b0 [sunrpc] > > 7) 536 40 svc_process+0x150/0x240 [sunrpc] > > 8) 496 72 svc_handle_xprt+0x4b0/0x5f0 [sunrpc] > > 9) 424 56 svc_recv+0x1b2/0x3a0 [sunrpc] > > 10) 368 80 nfsd+0x11c/0x3d0 [nfsd] > > 11) 288 56 kthread+0xe3/0x120 > > 12) 232 40 ret_from_fork+0x1a1/0x270 > > 13) 192 192 ret_from_fork_asm+0x1a/0x30 > >=20 > > Manually inspecting function graphs of vfs_getattr(), it looks like the= deepest > > function (that we can trace) is avc_lookup(), so here's a bpftrace scri= pt that > > prints the stack depth from avc_lookup() via nfsd4_deleg_getattr_confli= ct() > > (I mostly punted to Gemini for this): > >=20 > > # cat peak-usage.bt=20 > > kprobe:nfsd4_deleg_getattr_conflict { > > @in_deleg_conflict[tid] =3D 1; > > } > >=20 > > kprobe:avc_lookup /@in_deleg_conflict[tid]/ { > > $stack_size =3D (uint64)16384;=20 > > $sp =3D reg("sp"); > > $stack_base =3D $sp & ~($stack_size - 1); > > $total_used =3D $stack_base + $stack_size - $sp; > >=20 > > if ($total_used > @max_depth_bytes) { > > @max_depth_bytes =3D $total_used; > > @deepest_stack =3D kstack; > > } > > } > >=20 > > kretprobe:nfsd4_deleg_getattr_conflict { delete(@in_deleg_conflict[tid]= ); } > >=20 > > And finally the result: > >=20 > > # bpftrace peak-usage.bt=20 > > Attached 3 probes > > ^C > >=20 > > @deepest_stack:=20 > > avc_lookup+1 > > avc_has_perm_noaudit+60 > > avc_has_perm+89 > > selinux_inode_getattr+203 > > security_inode_getattr+70 > > vfs_getattr+35 > > nfsd4_deleg_getattr_conflict+958 > > nfsd4_encode_fattr4+401 > > nfsd4_encode_getattr+44 > > nfsd4_encode_operation+207 > > nfsd4_proc_compound+470 > > nfsd_dispatch+217 > > svc_process_common+1227 > > svc_process+336 > > svc_handle_xprt+1200 > > svc_recv+434 > > nfsd+284 > > kthread+227 > > ret_from_fork+417 > > ret_from_fork_asm+26 > >=20 > > @max_depth_bytes: 1792 >=20 > Since the new code only needs the file's size, perhaps you can get > away with >=20 > if (i_size_read(inode) !=3D ncf->ncf_cb_fsize) >=20 > rather than >=20 > err =3D vfs_getattr(path, stat, STATX_SIZE, AT_STATX_SYNC_AS_STAT= ); > if (err) { > status =3D nfserrno(err); > goto out_status; > } > if (stat->size !=3D ncf->ncf_cb_fsize) >=20 > Then there's no longer a need for a struct kstat at all. The client is > holding a delegation, so I would expect the file size to be stable. >=20 I hate relying on the size for this, since it's not a reliable indicator of change, especially on something that has a fixed size (VM image, for instance). In fact, I wonder if this ought to be looking at the mtime too. If the mtime that the client reported is later than the mtime the server has, then we can probably infer that there are buffered writes out there. --=20 Jeff Layton