Re: warning for EOPNOTSUPP vfs_copy_file_range

[Amir Goldstein]

On Fri, May 20, 2022 at 6:03 AM He Zhe <zhe.he@xxxxxxxxxxxxx> wrote:
>
>
>
> On 5/19/22 22:31, Luís Henriques wrote:
> > Amir Goldstein <amir73il@xxxxxxxxx> writes:
> >
> >> On Thu, May 19, 2022 at 11:22 AM He Zhe <zhe.he@xxxxxxxxxxxxx> wrote:
> >>> Hi,
> >>>
> >>> We are experiencing the following warning from
> >>> "WARN_ON_ONCE(ret == -EOPNOTSUPP);" in vfs_copy_file_range, from
> >>> 64bf5ff58dff ("vfs: no fallback for ->copy_file_range")
> >>>
> >>> # cat /sys/class/net/can0/phys_switch_id
> >>>
> >>> WARNING: CPU: 7 PID: 673 at fs/read_write.c:1516 vfs_copy_file_range+0x380/0x440
> >>> Modules linked in: llce_can llce_logger llce_mailbox llce_core sch_fq_codel
> >>> openvswitch nsh nf_conncount nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4
> >>> CPU: 7 PID: 673 Comm: cat Not tainted 5.15.38-yocto-standard #1
> >>> Hardware name: Freescale S32G399A (DT)
> >>> pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> >>> pc : vfs_copy_file_range+0x380/0x440
> >>> lr : vfs_copy_file_range+0x16c/0x440
> >>> sp : ffffffc00e0f3ce0
> >>> x29: ffffffc00e0f3ce0 x28: ffffff88157b5a40 x27: 0000000000000000
> >>> x26: ffffff8816ac3230 x25: ffffff881c060008 x24: 0000000000001000
> >>> x23: 0000000000000000 x22: 0000000000000000 x21: ffffff881cc99540
> >>> x20: ffffff881cc9a340 x19: ffffffffffffffa1 x18: ffffffffffffffff
> >>> x17: 0000000000000001 x16: 0000adfbb5178cde x15: ffffffc08e0f3647
> >>> x14: 0000000000000000 x13: 34613178302f3061 x12: 3178302b636e7973
> >>> x11: 0000000000058395 x10: 00000000fd1c5755 x9 : ffffffc008361950
> >>> x8 : ffffffc00a7d4d58 x7 : 0000000000000000 x6 : 0000000000000001
> >>> x5 : ffffffc009e81000 x4 : ffffffc009e817f8 x3 : 0000000000000000
> >>> x2 : 0000000000000000 x1 : ffffff88157b5a40 x0 : ffffffffffffffa1
> >>> Call trace:
> >>>  vfs_copy_file_range+0x380/0x440
> >>>  __do_sys_copy_file_range+0x178/0x3a4
> >>>  __arm64_sys_copy_file_range+0x34/0x4c
> >>>  invoke_syscall+0x5c/0x130
> >>>  el0_svc_common.constprop.0+0x68/0x124
> >>>  do_el0_svc+0x50/0xbc
> >>>  el0_svc+0x54/0x130
> >>>  el0t_64_sync_handler+0xa4/0x130
> >>>  el0t_64_sync+0x1a0/0x1a4
> >>> cat: /sys/class/net/can0/phys_switch_id: Operation not supported
> >>>
> >>> And we found this is triggered by the following stack. Specifically, all
> >>> netdev_ops in CAN drivers we can find now do not have ndo_get_port_parent_id and
> >>> ndo_get_devlink_port, which makes phys_switch_id_show return -EOPNOTSUPP all the
> >>> way back to vfs_copy_file_range.
> >>>
> >>> phys_switch_id_show+0xf4/0x11c
> >>> dev_attr_show+0x2c/0x6c
> >>> sysfs_kf_seq_show+0xb8/0x150
> >>> kernfs_seq_show+0x38/0x44
> >>> seq_read_iter+0x1c4/0x4c0
> >>> kernfs_fop_read_iter+0x44/0x50
> >>> generic_file_splice_read+0xdc/0x190
> >>> do_splice_to+0xa0/0xfc
> >>> splice_direct_to_actor+0xc4/0x250
> >>> do_splice_direct+0x94/0xe0
> >>> vfs_copy_file_range+0x16c/0x440
> >>> __do_sys_copy_file_range+0x178/0x3a4
> >>> __arm64_sys_copy_file_range+0x34/0x4c
> >>> invoke_syscall+0x5c/0x130
> >>> el0_svc_common.constprop.0+0x68/0x124
> >>> do_el0_svc+0x50/0xbc
> >>> el0_svc+0x54/0x130
> >>> el0t_64_sync_handler+0xa4/0x130
> >>> el0t_64_sync+0x1a0/0x1a4
> >>>
> >>> According to the original commit log, this warning is for operational validity
> >>> checks to generic_copy_file_range(). The reading will eventually return as
> >>> not supported as printed above. But is this warning still necessary? If so we
> >>> might want to remove it to have a cleaner dmesg.
> >>>
> >> Sigh! Those filesystems have no business doing copy_file_range()
> >>
> >> Here is a patch that Luis has been trying to push last year
> >> to fix a problem with copy_file_range() from tracefs:
> >>
> >> https://lore.kernel.org/linux-fsdevel/20210702090012.28458-1-lhenriques@xxxxxxx/
> > Yikes!  It's been a while and I completely forgot about it.  I can
> > definitely try to respin this patch if someone's interested in picking
> > it.  I'll have to go re-read everything again and see what's missing and
> > what has changed in between.
>
> Thank you both for quick replies.
>
> It would be good if this could be sorted out, as folks who are not familiar with
> it might be confused by the call trace. But if this is supposed to cost a long
> time, maybe we can first solve the false positive warning for the drivers in this
> case, as it seems the "operational validity checks" was not for these drivers.
>

Yes, technically, you are right.
Userspace should not be able to trigger a code validity assertion.
But the reason that assertion is there is to warn us developers
if we had overlooked a logic case and IMO we did.
The entire concept of calling ->copy_file_range() on random
filesystems has more than one problem and I would like for the kernel to
stop doing that.

Thanks,
Amir.