----- Original Message -----
> From: "CAI Qian" <caiqian@xxxxxxxxxx>
> To: "Al Viro" <viro@xxxxxxxxxxxxxxxxxx>
> Cc: "Linus Torvalds" <torvalds@xxxxxxxxxxxxxxxxxxxx>, "Dave Chinner"
> <david@xxxxxxxxxxxxx>, "linux-xfs"
> <linux-xfs@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx, "Jens Axboe" <axboe@xxxxxxxxx>,
> "Nick Piggin" <npiggin@xxxxxxxxx>,
> linux-fsdevel@xxxxxxxxxxxxxxx
> Sent: Friday, September 30, 2016 9:32:53 AM
> Subject: Re: [RFC][CFT] splice_read reworked
>
>
>
> ----- Original Message -----
> > From: "Al Viro" <viro@xxxxxxxxxxxxxxxxxx>
> > To: "Linus Torvalds" <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > Cc: "Dave Chinner" <david@xxxxxxxxxxxxx>, "CAI Qian" <caiqian@xxxxxxxxxx>,
> > "linux-xfs" <linux-xfs@xxxxxxxxxxxxxxx>,
> > xfs@xxxxxxxxxxx, "Jens Axboe" <axboe@xxxxxxxxx>, "Nick Piggin"
> > <npiggin@xxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx
> > Sent: Friday, September 23, 2016 3:00:32 PM
> > Subject: [RFC][CFT] splice_read reworked
> >
> > The series is supposed to solve the locking order problems for
> > ->splice_read() and get rid of code duplication between the read-side
> > methods.
> > pipe_lock is lifted out of ->splice_read() instances, along with
> > waiting for empty space in pipe, etc. - we do that stuff in callers.
> > A new variant of iov_iter is introduced - it's backed by a pipe,
> > copy_to_iter() results in allocating pages and copying into those,
> > copy_page_to_iter() just sticks a reference to that page into pipe.
> > Running out of space in pipe yields a short read, as a fault in
> > iovec-backed
> > iov_iter would have. Enough primitives are implemented for normal
> > ->read_iter() instances to work.
> > generic_file_splice_read() switched to feeding such iov_iter to
> > ->read_iter() instance. That turns out to be enough to kill almost all
> > ->splice_read() instances; the only ones _not_ using
> > generic_file_splice_read()
> > or default_file_splice_read() (== no zero-copy fallback) are
> > fuse_dev_splice_read(), 3 instances in kernel/{relay.c,trace/trace.c} and
> > sock_splice_read(). It's almost certainly possible to convert fuse one
> > and the same might be possible to do to socket one. relay and tracing
> > stuff is just plain weird; might or might not be doable.
> >
> > Something hopefully working is in
> > git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git
> > #work.splice_read
> Tested-by: CAI Qian <caiqian@xxxxxxxxxx>
Except...
One warning just pop up while running trinity.
[ 1599.151286] ------------[ cut here ]------------
[ 1599.156457] WARNING: CPU: 37 PID: 95143 at lib/iov_iter.c:316
sanity+0x75/0x80
[ 1599.164818] Modules linked in: af_key ieee802154_socket ieee802154
vmw_vsock_vmci_transport vsock vmw_vmci hidp cmtp kernelcapi bnep rfcomm
bluetooth rfkill can_bcm can_raw can pptp gre l2tp_ppp l2tp_netlink l2tp_core
ip6_udp_tunnel udp_tunnel pppoe pppox ppp_generic slhc nfnetlink
scsi_transport_iscsi atm sctp ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat
nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 xt_addrtype iptable_filter
xt_conntrack nf_nat nf_conntrack br_netfilter bridge stp llc overlay intel_rapl
sb_edac edac_core x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel kvm
irqbypass crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel lrw
gf128mul glue_helper ablk_helper cryptd iTCO_wdt iTCO_vendor_support pcspkr
mei_me sg i2c_i801 mei shpchp lpc_ich i2c_smbus ipmi_ssif wmi ipmi_si
ipmi_msghandler acpi_power_meter acpi_pad nfsd auth_rpcgss nfs_acl lockd grace
sunrpc ip_tables xfs libcrc32c sd_mod sr_mod cdrom mgag200 i2c_algo_bit
drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops crc32c_intel ttm
ixgbe drm ahci mdio libahci ptp libata i2c_core pps_core dca fjes dm_mirror
dm_region_hash dm_log dm_mod
[ 1599.278669] CPU: 50 PID: 95143 Comm: trinity-c142 Not tainted
4.8.0-rc8-usrns-scale+ #8
[ 1599.287604] Hardware name: Intel Corporation S2600WTT/S2600WTT, BIOS
GRNDSDP1.86B.0044.R00.1501191641 01/19/2015
[ 1599.298962] 0000000000000286 000000007794c41e ffff8803c6c7fbb0
ffffffff813d5e93
[ 1599.307259] 0000000000000000 0000000000000000 ffff8803c6c7fbf0
ffffffff8109c87b
[ 1599.315553] 0000013c00000000 0000000000000efe ffffea001de95240
ffff8802e1aca600
[ 1599.323847] Call Trace:
[ 1599.326580] [<ffffffff813d5e93>] dump_stack+0x85/0xc2
[ 1599.332315] [<ffffffff8109c87b>] __warn+0xcb/0xf0
[ 1599.337660] [<ffffffff8109c9ad>] warn_slowpath_null+0x1d/0x20
[ 1599.344171] [<ffffffff813e9b45>] sanity+0x75/0x80
[ 1599.349518] [<ffffffff813ec739>] copy_page_to_iter+0xf9/0x1e0
[ 1599.356027] [<ffffffff8120691f>] shmem_file_read_iter+0x9f/0x340
[ 1599.362829] [<ffffffff812bbeb9>] generic_file_splice_read+0xb9/0x1b0
[ 1599.370015] [<ffffffff812bc206>] do_splice_to+0x76/0x90
[ 1599.375941] [<ffffffff812bc2db>] splice_direct_to_actor+0xbb/0x220
[ 1599.382935] [<ffffffff812bba80>] ? generic_pipe_buf_nosteal+0x10/0x10
[ 1599.390220] [<ffffffff812bc4d8>] do_splice_direct+0x98/0xd0
[ 1599.396537] [<ffffffff81281dd1>] do_sendfile+0x1d1/0x3b0
[ 1599.402563] [<ffffffff81282973>] SyS_sendfile64+0x73/0xd0
[ 1599.408685] [<ffffffff81003f8c>] do_syscall_64+0x6c/0x1e0
[ 1599.414820] [<ffffffff817d927f>] entry_SYSCALL64_slow_path+0x25/0x25
[ 1599.422087] ---[ end trace a3fb2953df356f80 ]---
CAI Qian
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