On Sat, 2017-10-14 at 09:29 -0400, Chuck Lever wrote:
> > On Oct 14, 2017, at 6:38 AM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> >
> > On Sun, 2017-10-08 at 19:13 -0400, Chuck Lever wrote:
> > > 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@xxxxxxxxxx>
> > > Fixes: 5d252f90a800 ('svcrdma: Add class for RDMA backwards ... ')
> > > Cc: stable@xxxxxxxxxxxxxxx # v4.12
> > > Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> > > ---
> > > net/sunrpc/xprtrdma/svc_rdma_backchannel.c | 6 +++++-
> > > 1 file changed, 5 insertions(+), 1 deletion(-)
> > >
> > > Hi Ben, Jeff-
> > >
> > > I was able to reproduce the problem here with a rigged Linux client.
> > > This is my proposed fix. Fix also tested with a prototype Solaris
> > > client similar to the one that exposed the problem.
> > >
> > >
> > > diff --git a/net/sunrpc/xprtrdma/svc_rdma_backchannel.c b/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
> > > index ec37ad8..1854db2 100644
> > > --- a/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
> > > +++ b/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
> > > @@ -132,6 +132,10 @@ static int svc_rdma_bc_sendto(struct svcxprt_rdma *rdma,
> > > if (ret)
> > > goto out_err;
> > >
> > > + /* Bump page refcnt so Send completion doesn't release
> > > + * the rq_buffer before all retransmits are complete.
> > > + */
> > > + get_page(virt_to_page(rqst->rq_buffer));
> >
> > Looks fairly reasonable, but is this enough? Could rq_buffer be larger
> > than a page?
>
> Not in the current implementation. See xprt_rdma_bc_allocate.
>
> Thanks for the review!
>
No problem.
>
> > > ret = svc_rdma_post_send_wr(rdma, ctxt, 1, 0);
> > > if (ret)
> > > goto out_unmap;
> > > @@ -164,7 +168,6 @@ static int svc_rdma_bc_sendto(struct svcxprt_rdma *rdma,
> > > return -EINVAL;
> > > }
> > >
> > > - /* svc_rdma_sendto releases this page */
> > > page = alloc_page(RPCRDMA_DEF_GFP);
> > > if (!page)
> > > return -ENOMEM;
> > > @@ -183,6 +186,7 @@ static int svc_rdma_bc_sendto(struct svcxprt_rdma *rdma,
> > > {
> > > struct rpc_rqst *rqst = task->tk_rqstp;
> > >
> > > + put_page(virt_to_page(rqst->rq_buffer));
> > > kfree(rqst->rq_rbuffer);
> > > }
> > >
> > >
> >
> > --
> > Jeff Layton <jlayton@xxxxxxxxxx>
> > --
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>
> --
> Chuck Lever
>
>
>
Might be worth making sure the thing isn't larger than a page with a
WARN_ON, or at least a comment in there in case that ever changes.
Otherwise, I think this is fine:
Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
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