linux-kernel - Re: [lkp-robot] [debugfs] f3e7155d08: BUG:unable_to_handle

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Date:   Sun, 23 Apr 2017 20:37:14 +0200
From:   Nicolai Stange <nicstange@...il.com>
To:     kernel test robot <xiaolong.ye@...el.com>
Cc:     Nicolai Stange <nicstange@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Johannes Berg <johannes@...solutions.net>,
        "Paul E.McKenney" <paulmck@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, lkp@...org
Subject: Re: [lkp-robot] [debugfs]  f3e7155d08: BUG:unable_to_handle_kernel

Hi Xiaolong,

I'm encountering some difficulties running the reproducer, see below.
Any help is very welcome!

On Tue, Apr 18 2017, kernel test robot wrote:

> [   45.772683] BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
<snip>
> [   45.772697] IP: __debugfs_remove+0x5c/0xc0
> [   45.772743] Call Trace:
> [   45.772750]  debugfs_remove_recursive+0xd4/0x1e0
> [   45.772758]  rpc_clnt_debugfs_unregister+0x19/0x30
> [   45.772762]  rpc_client_register+0x18a/0x1c0
> [   45.772765]  rpc_new_client+0x1de/0x2e0
> [   45.772768]  rpc_create_xprt+0x58/0x170
> [   45.772769]  rpc_create+0xea/0x1c0
> [   45.772776]  nfs_create_rpc_client+0xe8/0x130
> [   45.772814]  nfs4_init_client+0x7e/0x290 [nfsv4]
> [   45.772820]  ? __radix_tree_replace+0x8a/0x140
> [   45.772823]  ? radix_tree_iter_tag_clear+0x1c/0x20
> [   45.772827]  ? __rpc_init_priority_wait_queue+0x81/0xb0
> [   45.772830]  ? rpc_init_wait_queue+0x13/0x20
> [   45.772847]  ? nfs4_alloc_client+0x1d2/0x1e0 [nfsv4]
<snip>
> [ 45.772985] Code: 8b 7c 24 30 48 89 de e8 f3 28 e6 ff 48 89 df e8 3b
> 22 e5 ff 4c 8b 63 78 48 c7 c2 20 d7 3b 82 48 c7 c6 e0 9f c9 81 49 8d
> 7c 24 18 <41> c7 44 24 10 00 00 00 00 4d 8d 6c 24 10 e8 a1 b6 cc ff 49
> 8d

Ok, that's

	41 c7 44 24 10 00 00 	movl   $0x0,0x10(%r12)

which is probably the init_completion() in __debugfs_remove_file():

	fsd = dentry->d_fsdata;
	init_completion(&fsd->active_users_drained);

This would mean that fsd == NULL and this can happen only if the dentry
in question isn't a regular file but a symlink or whatever. So, an
additional d_is_reg() is needed here. I'll fix this in the next
iteration once I got the reproducer working.

> To reproduce:
>
>         git clone https://github.com/01org/lkp-tests.git
>         cd lkp-tests
>         bin/lkp qemu -k <bzImage> job-script  # job-script is attached in this email
>

This gives

  make: Entering directory '/home/nic/lkp-tests/bin/event'
  gcc    -c -o wakeup.o wakeup.c
  gcc   -o wakeup wakeup.o
  rm -f wakeup.o
  strip wakeup
  make: Leaving directory '/home/nic/lkp-tests/bin/event'
  cpio: root:lkp: invalid group
  cpio: root:lkp: invalid group
  cpio: root:lkp: invalid group
  gzip: /home/nic/.lkp/cache/lkp-x86_64.cpio: No such file or directory
  mv: cannot stat ‘/home/nic/.lkp/cache/lkp-x86_64.cpio.gz’: No such file or directory
  mv: cannot stat ‘/home/nic/.lkp/cache/lkp-x86_64.cgz’: No such file or directory
  result_root: /home/nic/.lkp//result/boot/1/vm-lkp-nex04-8G/debian-x86_64-2016-08-31.cgz/x86_64-rhel-7.2/gcc-6/f3e7155d085591ab58f0993ce633fea58c082b35/3
  downloading initrds ...
  /usr/bin/wget -q --local-encoding=UTF-8 --retry-connrefused --waitretry 1000 --tries 1000 https://github.com/0day-ci/lkp-qemu/raw/master/osimage/debian/debian-x86_64-2016-08-31.cgz -N -P /home/nic/.lkp/cache/osimage/debian
  /usr/bin/wget -q --local-encoding=UTF-8 --retry-connrefused --waitretry 1000 --tries 1000 https://github.com/0day-ci/lkp-qemu/raw/master/osimage/deps/debian-x86_64-2016-08-31.cgz/lkp_2017-04-01.cgz -N -P /home/nic/.lkp/cache/osimage/deps/debian-x86_64-2016-08-31.cgz
  Failed to download osimage/deps/debian-x86_64-2016-08-31.cgz/lkp_2017-04-01.cgz

Manual download of that very last lkp_2017-04-01.cgz file results in a 404
error. Please let me know if you need more details.

Thank you!

Nicolai