Re: warning for EOPNOTSUPP vfs_copy_file_range

[Luís Henriques]

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.

Cheers,
-- 
Luís

> 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.
>