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Message-ID: <088333133e7cf377e66d86cb437eba068407f611.camel@kernel.org>
Subject: Re: [PATCH] nfsd: don't free files unconditionally in
 __nfsd_file_cache_purge
From:   Jeff Layton <jlayton@kernel.org>
To:     Chuck Lever <chuck.lever@oracle.com>
Cc:     Ruben Vestergaard <rubenv@drcmr.dk>,
        Torkil Svensgaard <torkil@drcmr.dk>,
        Shachar Kagan <skagan@nvidia.com>, linux-nfs@vger.kernel.org,
        linux-kernel@vger.kernel.org
Date:   Fri, 20 Jan 2023 13:36:30 -0500
In-Reply-To: <20230119192021.83578-1-jlayton@kernel.org>
References: <20230119192021.83578-1-jlayton@kernel.org>
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On Thu, 2023-01-19 at 14:20 -0500, Jeff Layton wrote:
> nfsd_file_cache_purge is called when the server is shutting down, in
> which case, tearing things down is generally fine, but it also gets
> called when the exports cache is flushed.
>=20
> Instead of walking the cache and freeing everything unconditionally,
> attempt to unhash each entry and get a reference to it, and then put
> that reference. Only queue it to the dispose list if the refcount goes
> to 0.
>=20
> Fixes: ac3a2585f018 ("nfsd: rework refcounting in filecache")
> Reported-by: Ruben Vestergaard <rubenv@drcmr.dk>
> Reported-by: Torkil Svensgaard <torkil@drcmr.dk>
> Reported-by: Shachar Kagan <skagan@nvidia.com>
> Signed-off-by: Jeffrey Layton <jlayton@kernel.org>
> ---
>  fs/nfsd/filecache.c | 21 ++++++++++++++++++---
>  1 file changed, 18 insertions(+), 3 deletions(-)
>=20
> I was able to reproduce this today by running pynfs against the server
> while running "exportfs -ra" in a loop. This one is a bit different in
> that it happened in the open codepath, but that's probably just because
> delegations are more likely to be long-lived. With this patch, the
> server survives the run:
>=20
> [  337.962027] ------------[ cut here ]------------
> [  337.963823] refcount_t: underflow; use-after-free.
> [  337.965502] WARNING: CPU: 6 PID: 3401 at lib/refcount.c:28 refcount_wa=
rn_saturate+0xba/0x110
> [  337.967999] Modules linked in: nfsd(E) auth_rpcgss(E) nfs_acl(E) lockd=
(E) grace(E) sunrpc(E) nls_iso8859_1(E) nls_cp437(E) vfat(E) fat(E) ext4(E)=
 crc16(E) cirrus(E) kvm_intel(E) 9p(E) mbcache(E) joydev(E) virtio_net(E) d=
rm_shmem_helper(E) net_failover(E) kvm(E) jbd2(E) netfs(E) psmouse(E) evdev=
(E) pcspkr(E) failover(E) irqbypass(E) virtio_balloon(E) drm_kms_helper(E) =
9pnet_virtio(E) button(E) drm(E) configfs(E) zram(E) zsmalloc(E) crct10dif_=
pclmul(E) crc32_pclmul(E) nvme(E) ghash_clmulni_intel(E) virtio_blk(E) sha5=
12_ssse3(E) sha512_generic(E) nvme_core(E) t10_pi(E) virtio_pci(E) virtio(E=
) crc64_rocksoft_generic(E) aesni_intel(E) crypto_simd(E) crc64_rocksoft(E)=
 virtio_pci_legacy_dev(E) i6300esb(E) cryptd(E) serio_raw(E) crc64(E) virti=
o_pci_modern_dev(E) virtio_ring(E) btrfs(E) blake2b_generic(E) xor(E) raid6=
_pq(E) libcrc32c(E) crc32c_generic(E) crc32c_intel(E) autofs4(E)
> [  337.992040] CPU: 6 PID: 3401 Comm: nfsd Tainted: G            E      6=
.2.0-rc3+ #11
> [  337.994701] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1=
.16.1-2.fc37 04/01/2014
> [  337.998046] RIP: 0010:refcount_warn_saturate+0xba/0x110
> [  337.999852] Code: 01 01 e8 83 e5 4f 00 0f 0b c3 cc cc cc cc 80 3d 60 f=
4 05 01 00 75 85 48 c7 c7 30 b5 e1 9d c6 05 50 f4 05 01 01 e8 60 e5 4f 00 <=
0f> 0b c3 cc cc cc cc 80 3d 3b f4 05 01 00 0f 85 5e ff ff ff 48 c7
> [  338.005245] RSP: 0018:ffffa36802e4bd50 EFLAGS: 00010282
> [  338.006621] RAX: 0000000000000000 RBX: 0000000000000008 RCX: 000000000=
0000000
> [  338.008273] RDX: 0000000000000001 RSI: ffffffff9de03ef5 RDI: 00000000f=
fffffff
> [  338.009804] RBP: 0000000000000003 R08: 0000000000000000 R09: ffffa3680=
2e4bc00
> [  338.011719] R10: 0000000000000003 R11: ffffffff9e0bfdc8 R12: ffff9578d=
a461b80
> [  338.013533] R13: 0000000000000001 R14: ffff9578da422280 R15: ffff9578d=
a461b80
> [  338.015238] FS:  0000000000000000(0000) GS:ffff957a37d00000(0000) knlG=
S:0000000000000000
> [  338.017179] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  338.018680] CR2: 00007f324c1e1c08 CR3: 000000020360a004 CR4: 000000000=
0060ee0
> [  338.020377] Call Trace:
> [  338.021190]  <TASK>
> [  338.021956]  release_all_access+0x96/0x120 [nfsd]
> [  338.023192]  ? _raw_spin_unlock+0x15/0x30
> [  338.024192]  nfsd4_close+0x275/0x3d0 [nfsd]
> [  338.025468]  ? fh_verify+0x45e/0x780 [nfsd]
> [  338.027535]  ? __pfx_nfsd4_encode_noop+0x10/0x10 [nfsd]
> [  338.028775]  ? nfsd4_encode_operation+0xae/0x280 [nfsd]
> [  338.030593]  nfsd4_proc_compound+0x3ae/0x6f0 [nfsd]
> [  338.032341]  nfsd_dispatch+0x16a/0x270 [nfsd]
> [  338.034667]  svc_process_common+0x2eb/0x660 [sunrpc]
> [  338.036614]  ? __pfx_nfsd_dispatch+0x10/0x10 [nfsd]
> [  338.038827]  ? __pfx_nfsd+0x10/0x10 [nfsd]
> [  338.040267]  svc_process+0xad/0x100 [sunrpc]
> [  338.041981]  nfsd+0xd5/0x190 [nfsd]
> [  338.043362]  kthread+0xe9/0x110
> [  338.044680]  ? __pfx_kthread+0x10/0x10
> [  338.046376]  ret_from_fork+0x2c/0x50
> [  338.047892]  </TASK>
> [  338.049067] ---[ end trace 0000000000000000 ]---
> [  760.792789] BUG: kernel NULL pointer dereference, address: 00000000000=
00078
> [  760.795933] #PF: supervisor read access in kernel mode
> [  760.797477] #PF: error_code(0x0000) - not-present page
> [  760.799120] PGD 0 P4D 0
> [  760.800140] Oops: 0000 [#1] PREEMPT SMP PTI
> [  760.801383] CPU: 2 PID: 3401 Comm: nfsd Tainted: G        W   E      6=
.2.0-rc3+ #11
> [  760.803120] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1=
.16.1-2.fc37 04/01/2014
> [  760.805018] RIP: 0010:filp_close+0x23/0x70
> [  760.806099] Code: 90 90 90 90 90 90 90 0f 1f 44 00 00 41 54 55 53 48 8=
b 47 38 48 85 c0 0f 84 41 e1 6d 00 48 8b 47 28 48 89 fb 48 89 f5 45 31 e4 <=
48> 8b 40 78 48 85 c0 74 08 e8 6f 70 72 00 41 89 c4 f6 43 45 40 75
> [  760.809737] RSP: 0018:ffffa36802e4bc78 EFLAGS: 00010246
> [  760.811084] RAX: 0000000000000000 RBX: ffff9578c7d4d600 RCX: 000000000=
0000000
> [  760.812540] RDX: 000000000000098d RSI: 0000000000000000 RDI: ffff9578c=
7d4d600
> [  760.814433] RBP: 0000000000000000 R08: 0000011335048e60 R09: ffff9578f=
82f1540
> [  760.816089] R10: ffffa36802e4bcd0 R11: ffffa36802e4bcd8 R12: 000000000=
0000000
> [  760.817529] R13: 0000000000000001 R14: dead000000000100 R15: ffff9578f=
82f1558
> [  760.818982] FS:  0000000000000000(0000) GS:ffff957a37c80000(0000) knlG=
S:0000000000000000
> [  760.820544] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  760.821734] CR2: 0000000000000078 CR3: 00000001565ce002 CR4: 000000000=
0060ee0
> [  760.823141] Call Trace:
> [  760.823808]  <TASK>
> [  760.824419]  nfsd_file_free+0xe9/0x210 [nfsd]
> [  760.825610]  release_all_access+0x96/0x120 [nfsd]
> [  760.826680]  nfs4_free_ol_stateid+0x22/0x60 [nfsd]
> [  760.827747]  free_ol_stateid_reaplist+0x61/0x90 [nfsd]
> [  760.828858]  release_openowner+0x258/0x2a0 [nfsd]
> [  760.829792]  __destroy_client+0x183/0x290 [nfsd]
> [  760.830694]  nfsd4_setclientid_confirm+0x1a3/0x4f0 [nfsd]
> [  760.831763]  nfsd4_proc_compound+0x3ae/0x6f0 [nfsd]
> [  760.832717]  nfsd_dispatch+0x16a/0x270 [nfsd]
> [  760.833576]  svc_process_common+0x2eb/0x660 [sunrpc]
> [  760.834587]  ? __pfx_nfsd_dispatch+0x10/0x10 [nfsd]
> [  760.835576]  ? __pfx_nfsd+0x10/0x10 [nfsd]
> [  760.836462]  svc_process+0xad/0x100 [sunrpc]
> [  760.837317]  nfsd+0xd5/0x190 [nfsd]
> [  760.838133]  kthread+0xe9/0x110
> [  760.838862]  ? __pfx_kthread+0x10/0x10
> [  760.839755]  ret_from_fork+0x2c/0x50
> [  760.840534]  </TASK>
> [  760.841167] Modules linked in: nfsd(E) auth_rpcgss(E) nfs_acl(E) lockd=
(E) grace(E) sunrpc(E) nls_iso8859_1(E) nls_cp437(E) vfat(E) fat(E) ext4(E)=
 crc16(E) cirrus(E) kvm_intel(E) 9p(E) mbcache(E) joydev(E) virtio_net(E) d=
rm_shmem_helper(E) net_failover(E) kvm(E) jbd2(E) netfs(E) psmouse(E) evdev=
(E) pcspkr(E) failover(E) irqbypass(E) virtio_balloon(E) drm_kms_helper(E) =
9pnet_virtio(E) button(E) drm(E) configfs(E) zram(E) zsmalloc(E) crct10dif_=
pclmul(E) crc32_pclmul(E) nvme(E) ghash_clmulni_intel(E) virtio_blk(E) sha5=
12_ssse3(E) sha512_generic(E) nvme_core(E) t10_pi(E) virtio_pci(E) virtio(E=
) crc64_rocksoft_generic(E) aesni_intel(E) crypto_simd(E) crc64_rocksoft(E)=
 virtio_pci_legacy_dev(E) i6300esb(E) cryptd(E) serio_raw(E) crc64(E) virti=
o_pci_modern_dev(E) virtio_ring(E) btrfs(E) blake2b_generic(E) xor(E) raid6=
_pq(E) libcrc32c(E) crc32c_generic(E) crc32c_intel(E) autofs4(E)
> [  760.853527] CR2: 0000000000000078
> [  760.854340] ---[ end trace 0000000000000000 ]---
> [  760.855261] RIP: 0010:filp_close+0x23/0x70
> [  760.856185] Code: 90 90 90 90 90 90 90 0f 1f 44 00 00 41 54 55 53 48 8=
b 47 38 48 85 c0 0f 84 41 e1 6d 00 48 8b 47 28 48 89 fb 48 89 f5 45 31 e4 <=
48> 8b 40 78 48 85 c0 74 08 e8 6f 70 72 00 41 89 c4 f6 43 45 40 75
> [  760.859350] RSP: 0018:ffffa36802e4bc78 EFLAGS: 00010246
> [  760.860356] RAX: 0000000000000000 RBX: ffff9578c7d4d600 RCX: 000000000=
0000000
> [  760.861628] RDX: 000000000000098d RSI: 0000000000000000 RDI: ffff9578c=
7d4d600
> [  760.862898] RBP: 0000000000000000 R08: 0000011335048e60 R09: ffff9578f=
82f1540
> [  760.864172] R10: ffffa36802e4bcd0 R11: ffffa36802e4bcd8 R12: 000000000=
0000000
> [  760.865438] R13: 0000000000000001 R14: dead000000000100 R15: ffff9578f=
82f1558
> [  760.866692] FS:  0000000000000000(0000) GS:ffff957a37c80000(0000) knlG=
S:0000000000000000
> [  760.868053] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  760.869102] CR2: 0000000000000078 CR3: 00000001565ce002 CR4: 000000000=
0060ee0
>=20
> diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
> index 66449c41b19c..b9100707d347 100644
> --- a/fs/nfsd/filecache.c
> +++ b/fs/nfsd/filecache.c
> @@ -908,9 +908,24 @@ __nfsd_file_cache_purge(struct net *net)
>  		nf =3D rhashtable_walk_next(&iter);
>  		while (!IS_ERR_OR_NULL(nf)) {
>  			if (!net || nf->nf_net =3D=3D net) {
> -				nfsd_file_unhash(nf);
> -				nfsd_file_lru_remove(nf);
> -				list_add(&nf->nf_lru, &dispose);
> +				/* Ignore it if it's no longer hashed */
> +				if (!nfsd_file_unhash(nf))
> +					continue;
> +
> +				/*
> +				 * Try to claim the LRU ref (if any). If it's
> +				 * not on the LRU, then try to take a ref. If that
> +				 * fails, then we'll ignore it.
> +				 */
> +				if (!nfsd_file_lru_remove(nf))
> +					nf =3D nfsd_file_get(nf);
> +

Now that I've looked over this again today, I think this patch is not
quite right. We don't want to try to dequeue it from the lru until we
hold a reference, or we could corrupt the list_head for private users.

I think we want to do the same thing we do when we get a notifier pop in
this case. I'm working on a v2 now and will send it once I've tested it.

Cheers,

> +				/*
> +				 * Now try to put the ref we hold. If that works
> +				 * and it goes to zero, queue it to be freed.
> +				 */
> +				if (nf && refcount_dec_and_test(&nf->nf_ref))
> +					list_add(&nf->nf_lru, &dispose);
>  			}
>  			nf =3D rhashtable_walk_next(&iter);
>  		}

--=20
Jeff Layton <jlayton@kernel.org>