svcrdma: Preserve CB send buffer across retransmits

svcrdma: Preserve CB send buffer across retransmits

commit 0bad47cada5defba13e98827d22d06f13258dfb3 upstream.

During each NFSv4 callback Call, an RDMA Send completion frees the
page that contains the RPC Call message. If the upper layer
determines that a retransmit is necessary, this is too soon.

One possible symptom: after a GARBAGE_ARGS response an NFSv4.1
callback request, the following BUG fires on the NFS server:

kernel: BUG: Bad page state in process kworker/0:2H  pfn:7d3ce2
kernel: page:ffffea001f4f3880 count:-2 mapcount:0 mapping:          (null) index:0x0
kernel: flags: 0x2fffff80000000()
kernel: raw: 002fffff80000000 0000000000000000 0000000000000000 fffffffeffffffff
kernel: raw: dead000000000100 dead000000000200 0000000000000000 0000000000000000
kernel: page dumped because: nonzero _refcount
kernel: Modules linked in: cts rpcsec_gss_krb5 ocfs2_dlmfs ocfs2_stack_o2cb ocfs2_dlm
ocfs2_nodemanager ocfs2_stackglue rpcrdm a ib_ipoib rdma_ucm ib_ucm ib_uverbs ib_umad
rdma_cm ib_cm iw_cm x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel
kvm irqbypass crct10dif_pc lmul crc32_pclmul ghash_clmulni_intel pcbc iTCO_wdt
iTCO_vendor_support aesni_intel crypto_simd glue_helper cryptd pcspkr lpc_ich i2c_i801
mei_me mf d_core mei raid0 sg wmi ioatdma ipmi_si ipmi_devintf ipmi_msghandler shpchp
acpi_power_meter acpi_pad nfsd nfs_acl lockd auth_rpcgss grace sunrpc ip_tables xfs
libcrc32c mlx4_en mlx4_ib mlx5_ib ib_core sd_mod sr_mod cdrom ast drm_kms_helper
syscopyarea sysfillrect sysimgblt fb_sys_fops ttm ahci crc32c_intel libahci drm
mlx5_core igb libata mlx4_core dca i2c_algo_bit i2c_core nvme
kernel: ptp nvme_core pps_core dm_mirror dm_region_hash dm_log dm_mod dax
kernel: CPU: 0 PID: 11495 Comm: kworker/0:2H Not tainted 4.14.0-rc3-00001-g577ce48 #811
kernel: Hardware name: Supermicro Super Server/X10SRL-F, BIOS 1.0c 09/09/2015
kernel: Workqueue: ib-comp-wq ib_cq_poll_work [ib_core]
kernel: Call Trace:
kernel: dump_stack+0x62/0x80
kernel: bad_page+0xfe/0x11a
kernel: free_pages_check_bad+0x76/0x78
kernel: free_pcppages_bulk+0x364/0x441
kernel: ? ttwu_do_activate.isra.61+0x71/0x78
kernel: free_hot_cold_page+0x1c5/0x202
kernel: __put_page+0x2c/0x36
kernel: svc_rdma_put_context+0xd9/0xe4 [rpcrdma]
kernel: svc_rdma_wc_send+0x50/0x98 [rpcrdma]

This issue exists all the way back to v4.5, but refactoring and code
re-organization prevents this simple patch from applying to kernels
older than v4.12. The fix is the same, however, if someone needs to
backport it.

Reported-by: Ben Coddington <bcodding@redhat.com>
BugLink: https://bugzilla.linux-nfs.org/show_bug.cgi?id=314
Fixes: 5d252f90a800 ('svcrdma: Add class for RDMA backwards ... ')
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>