[PATCH net 3/5] netdevsim: avoid debugfs warning message when module is remove

[Taehee Yoo <ap420073@gmail.com>]

When module is being removed, it couldn't be held by try_module_get().
debugfs's open function internally tries to hold file_operation->owner
if .owner is set.
If holding owner operation is failed, it prints a warning message.

Test commands:
    #SHELL1
    while :
    do
        modprobe netdevsim
        echo 1 > /sys/bus/netdevsim/new_device
        modprobe -rv netdevsim
    done

    #SHELL2
    while :
    do
        cat /sys/kernel/debug/netdevsim/netdevsim1/ports/0/ipsec
    done

Splat looks like:
[  412.227709][ T1720] debugfs file owner did not clean up at exit: ipsec
[  412.227728][ T1720] WARNING: CPU: 3 PID: 1720 at fs/debugfs/file.c:309 full_proxy_open+0x10f/0x650
[  412.231755][ T1720] Modules linked in: netdevsim(-) veth openvswitch nsh nf_conncount nf_nat nf_conntrack nf_d]
[  412.236495][ T1720] CPU: 3 PID: 1720 Comm: cat Tainted: G    B   W         5.5.0-rc5+ #270
[  412.237468][ T1720] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
[  412.239480][ T1720] RIP: 0010:full_proxy_open+0x10f/0x650
[  412.240321][ T1720] Code: 48 c1 ea 03 80 3c 02 00 0f 85 c1 04 00 00 49 8b 3c 24 e8 24 fb 78 ff 84 c0 75 2d 4c 8
[  412.247099][ T1720] RSP: 0018:ffff8880c9787a38 EFLAGS: 00010286
[  412.247905][ T1720] RAX: dffffc0000000008 RBX: ffff8880ccb94b80 RCX: ffffffff912c2234
[  412.248961][ T1720] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff93d6dcf4
[  412.252583][ T1720] RBP: 0000000000000000 R08: fffffbfff2722f5d R09: fffffbfff2722f5d
[  412.253677][ T1720] R10: 0000000000000001 R11: fffffbfff2722f5c R12: ffffffffc02a7a80
[  412.258939][ T1720] R13: ffff8880acd07728 R14: ffff8880ae9a9b60 R15: ffffffff931b3b60
[  412.260021][ T1720] FS:  00007f24a0b9c540(0000) GS:ffff8880da800000(0000) knlGS:0000000000000000
[  412.261208][ T1720] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  412.262131][ T1720] CR2: 0000561898255068 CR3: 00000000c6a6c004 CR4: 00000000000606e0
[  412.263201][ T1720] Call Trace:
[  412.263650][ T1720]  do_dentry_open+0x63c/0xf50
[  412.264304][ T1720]  ? open_proxy_open+0x270/0x270
[  412.265015][ T1720]  ? __x64_sys_fchdir+0x180/0x180
[  412.265708][ T1720]  ? inode_permission+0x65/0x390
[  412.266566][ T1720]  path_openat+0x701/0x2810
[  412.267445][ T1720]  ? save_stack+0x69/0x80
[  412.268288][ T1720]  ? path_lookupat+0x880/0x880
[  412.269218][ T1720]  ? getname_flags+0xba/0x500
[  412.270556][ T1720]  ? do_sys_open+0x15d/0x350
[  412.271195][ T1720]  ? do_syscall_64+0x99/0x4f0
[  412.271843][ T1720]  ? entry_SYSCALL_64_after_hwframe+0x49/0xbe
[  412.272676][ T1720]  ? _raw_spin_unlock+0x1f/0x30
[  412.273349][ T1720]  ? deactivate_slab.isra.77+0x62e/0x800
[  412.274149][ T1720]  ? check_object+0xaf/0x260
[  412.274784][ T1720]  ? init_object+0x6b/0x80
[  412.275385][ T1720]  do_filp_open+0x17a/0x270
[ ... ]

In order to avoid the warning message, this patch makes netdevsim module
does not set .owner. Unsetting .owner is safe because these are protected
by inode_lock().

Fixes: 7699353da875 ("netdevsim: add ipsec offload testing")
Fixes: 31d3ad832948 ("netdevsim: add bpf offload support")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
---
 drivers/net/netdevsim/bpf.c   | 13 ++++++++++++-
 drivers/net/netdevsim/ipsec.c |  1 -
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/net/netdevsim/bpf.c b/drivers/net/netdevsim/bpf.c
index 2b74425822ab..13e17c82d71c 100644
--- a/drivers/net/netdevsim/bpf.c
+++ b/drivers/net/netdevsim/bpf.c
@@ -57,7 +57,18 @@ static int nsim_bpf_string_show(struct seq_file *file, void *data)
 
 	return 0;
 }
-DEFINE_SHOW_ATTRIBUTE(nsim_bpf_string);
+
+static int nsim_debugfs_bpf_string_open(struct inode *inode, struct file *f)
+{
+	return single_open(f, nsim_bpf_string_show, inode->i_private);
+}
+
+static const struct file_operations nsim_bpf_string_fops = {
+	.open = nsim_debugfs_bpf_string_open,
+	.release = single_release,
+	.read = seq_read,
+	.llseek = seq_lseek
+};
 
 static int
 nsim_bpf_verify_insn(struct bpf_verifier_env *env, int insn_idx, int prev_insn)
diff --git a/drivers/net/netdevsim/ipsec.c b/drivers/net/netdevsim/ipsec.c
index e27fc1a4516d..63aff6399d11 100644
--- a/drivers/net/netdevsim/ipsec.c
+++ b/drivers/net/netdevsim/ipsec.c
@@ -60,7 +60,6 @@ static ssize_t nsim_dbg_netdev_ops_read(struct file *filp,
 }
 
 static const struct file_operations ipsec_dbg_fops = {
-	.owner = THIS_MODULE,
 	.open = simple_open,
 	.read = nsim_dbg_netdev_ops_read,
 };
-- 
2.17.1