Re: warning for EOPNOTSUPP vfs_copy_file_range

[Amir Goldstein <amir73il@gmail.com>]

On Thu, May 19, 2022 at 11:22 AM He Zhe <zhe.he@windriver.com> 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@suse.de/

Luis gave up on it, because no maintainer stepped up to take
the patch, but I think that is the right way to go.

Maybe this bug report can raise awareness to that old patch.

Al, could you have a look?

Thanks,
Amir.