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From:   Scott Mayhew <smayhew@redhat.com>
To:     trond.myklebust@hammerspace.com, anna@kernel.org
Cc:     linux-nfs@vger.kernel.org
Subject: [PATCH 0/1] Fix potential oops in nfs_inode_remove_request()
Date:   Tue, 25 Jul 2023 11:08:06 -0400
Message-ID: <20230725150807.8770-1-smayhew@redhat.com>
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IBM reported a panic in nfs_inode_remove_request() while running LTP
(based on the the NFS mounts and the processes in the vmcore I'm pretty
sure it was in the nfslock3t_01 test):

BUG: Kernel NULL pointer dereference on read at 0x00000000
Faulting instruction address: 0xc008000005015600
Oops: Kernel access of bad area, sig: 11 [#1]
LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries
Modules linked in: loop dummy can_bcm can vcan can_dev veth vsock_loopback vmw_vsock_virtio_transport_common vsock tun tcp_dctcp nft_limit xt_limit xt_multiport xt_LOG nf_log_syslog n_hdlc sch_netem tcp_bbr overlay exfat vfat fat squashfs brd uinput snd_hrtimer snd_seq snd_timer snd_seq_device snd soundcore sctp_diag sctp xt_sctp act_tunnel_key nft_tunnel tunnel6 ip6_udp_tunnel xfrm4_tunnel udp_tunnel tunnel4 ip_tunnel xt_dccp xfrm_ipcomp nft_xfrm ext4 mbcache jbd2 nft_counter nft_compat nf_tables nfnetlink rpcsec_gss_krb5 nfsv4 dns_resolver rpadlpar_io rpaphp xsk_diag rpcrdma rdma_cm iw_cm ib_cm nfsv3 ib_core nfs bonding fscache netfs tls rfkill binfmt_misc pseries_rng nfsd auth_rpcgss nfs_acl lockd grace sunrpc drm drm_panel_orientation_quirks xfs libcrc32c dm_service_time sd_mod t10_pi sg ibmvfc ibmvnic scsi_transport_fc vmx_crypto pseries_wdt dm_multipath dm_mirror dm_region_hash dm_log dm_mod fuse [last unloaded: ltp_fw_load]
CPU: 0 PID: 3878459 Comm: kworker/u128:7 Tainted: G           OE     -------  ---  5.14.0-316.el9.ppc64le #1
Workqueue: nfsiod rpc_async_release [sunrpc]
NIP:  c008000005015600 LR: c008000005015598 CTR: c000000000f6d9d0
REGS: c0000001aecd3840 TRAP: 0300   Tainted: G           OE     -------  ---   (5.14.0-316.el9.ppc64le)
MSR:  800000000280b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE>  CR: 24002820  XER: 00000001
CFAR: c0080000050155bc DAR: 0000000000000000 DSISR: 40000000 IRQMASK: 0 
GPR00: c008000005015598 c0000001aecd3ae0 c008000005069000 0000000000000000 
GPR04: 0000000000000001 0000000000000000 0000000000000000 0000000000000005 
GPR08: 0000000000000001 0000000000000000 0000000000000002 c008000005033420 
GPR12: c000000000f6d9d0 c000000002eb0000 c0000000001876a8 c000000150c7e200 
GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 
GPR20: 0000000000000000 c000000002c1d238 0000000000000000 c000000002650e40 
GPR24: c00000008a941b74 0000000000000000 c0000006774cafd0 c0000006774cafe0 
GPR28: c008000001ee26f0 c00c000001d49580 c0000006774cae00 c00000016fb2a600 
NIP [c008000005015600] nfs_inode_remove_request+0x1c8/0x240 [nfs]
LR [c008000005015598] nfs_inode_remove_request+0x160/0x240 [nfs]
Call Trace:
[c0000001aecd3ae0] [c008000005015464] nfs_inode_remove_request+0x2c/0x240 [nfs] (unreliable)
[c0000001aecd3b30] [c008000005015d50] nfs_commit_release_pages+0x298/0x410 [nfs]
[c0000001aecd3c00] [c008000005013250] nfs_commit_release+0x38/0x80 [nfs]
[c0000001aecd3c30] [c008000001e53410] rpc_free_task+0x58/0xc0 [sunrpc]
[c0000001aecd3c60] [c008000001e534b8] rpc_async_release+0x40/0x70 [sunrpc]
[c0000001aecd3c90] [c00000000017a0b8] process_one_work+0x298/0x580
[c0000001aecd3d30] [c00000000017aa48] worker_thread+0xa8/0x620
[c0000001aecd3dc0] [c0000000001877c4] kthread+0x124/0x130
[c0000001aecd3e10] [c00000000000cd64] ret_from_kernel_thread+0x5c/0x64
Instruction dump:
e8410018 4800002c 60000000 60000000 e9230008 3949ffff 71290001 7c63509e 
e9230000 75290008 4082ffc8 e8630018 <e9230000> 3929ff38 7d4048a8 314affff 
---[ end trace 2902c6562da6500b ]---

In the vmcore, I can see that the folio->mapping was NULL:

crash> nfs_page.wb_folio c00000016fb2a600
    wb_folio = 0xc00c000001d49580
crash> folio.mapping 0xc00c000001d49580
      mapping = 0x0,

Note that I have *not* been able to reproduce the panic myself, but it
looks to me like once nfs_inode_remove_request() calls
folio_clear_private(), another process can come in and clobber the
folio->mapping, for example:

nfs_file_write
  nfs_clear_invalid_mapping
    nfs_invalidate_mapping
      invalidate_inode_pages2
        invalidate_inode_pages2_range
          invalidate_complete_folio2
            __filemap_remove_folio

or:

drop_pagecache_sb
  invalidate_mapping_pages
    invalidate_mapping_pagevec
      mapping_evict_folio
        remove_mapping
          __remove_mapping
            __filemap_remove_folio

So the nfs_inode should probably be initialized in the beginning of
nfs_inode_remove_request(), which is what it used to do before commit 
0c493b5cf16e.

Scott Mayhew (1):
  NFS: Fix potential oops in nfs_inode_remove_request()

 fs/nfs/write.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

-- 
2.41.0