[PATCH] scsi_dh: Use module_request_nowait

[Laura Abbott <labbott@fedoraproject.org>]

We recevied a bugzilla report:

Additional info:
reporter: libreport-2.6.3
WARNING: CPU: 3 PID: 10195 at kernel/kmod.c:140
__request_module+0x214/0x330()
Modules linked in: uas usb_storage xfs libcrc32c vhost_net vhost macvtap
macvlan bnep bluetooth pppoe pppox ppp_generic slhc xt_CHECKSUM
ipt_MASQUERADE nf_nat_masquerade_ipv4 tun ip6t_rpfilter ip6t_REJECT
nf_reject_ipv6 xt_conntrack ebtable_nat ebtable_filter ebtable_broute
bridge ebtables ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6
nf_nat_ipv6 ip6table_raw ip6table_security ip6table_mangle
ip6table_filter ip6_tables iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4
nf_nat_ipv4 nf_nat nf_conntrack iptable_raw iptable_security
iptable_mangle vfat fat joydev snd_hda_codec_realtek
snd_hda_codec_generic snd_hda_codec_hdmi snd_hda_intel btrfs
snd_hda_codec snd_hda_core snd_hwdep xor snd_seq raid6_pq intel_rapl
iosf_mbi eeepc_wmi x86_pkg_temp_thermal coretemp iTCO_wdt
iTCO_vendor_support kvm_intel
snd_seq_device asus_wmi sparse_keymap snd_pcm rfkill mxm_wmi kvm
crct10dif_pclmul snd_timer crc32_pclmul crc32c_intel snd mei_me mei
i2c_i801 lpc_ich soundcore shpchp soc_button_array tpm_infineon tpm_tis
tpm wmi nfsd auth_rpcgss nfs_acl lockd grace sunrpc 8021q garp stp llc
mrp i915 i2c_algo_bit serio_raw drm_kms_helper e1000e drm ptp pps_core
fjes video
CPU: 3 PID: 10195 Comm: kworker/u16:2 Not tainted
4.3.0-0.rc6.git2.1.fc24.x86_64 #1
Hardware name: ASUS All Series/Z87-PLUS, BIOS 1207 07/01/2013
Workqueue: events_unbound async_run_entry_fn
0000000000000000 0000000059576eea ffff880227a67b58 ffffffff81419a49
0000000000000000 ffff880227a67b90 ffffffff810a9c12 ffffffff81ce2ee5
0000000000000001 ffff88003f587000 0000000000000000 0000000000000000
Call Trace:
[<ffffffff81419a49>] dump_stack+0x4b/0x72
[<ffffffff810a9c12>] warn_slowpath_common+0x82/0xc0
[<ffffffff810a9d5a>] warn_slowpath_null+0x1a/0x20
[<ffffffff810c3f64>] __request_module+0x214/0x330
[<ffffffff81123a8d>] ? debug_lockdep_rcu_enabled+0x1d/0x20
[<ffffffff815bb32e>] scsi_dh_lookup+0x2e/0x40
[<ffffffff815bb870>] scsi_dh_add_device+0xd0/0x100
[<ffffffff815b766e>] scsi_sysfs_add_sdev+0xbe/0x2a0
[<ffffffff815a82e6>] ? __scsi_iterate_devices+0x66/0xd0
[<ffffffff815b5e5e>] do_scan_async+0x12e/0x170
[<ffffffff810d355a>] async_run_entry_fn+0x4a/0x140
[<ffffffff810c8470>] process_one_work+0x230/0x6a0
[<ffffffff810c83d9>] ? process_one_work+0x199/0x6a0
[<ffffffff810c892e>] worker_thread+0x4e/0x450
[<ffffffff810c88e0>] ? process_one_work+0x6a0/0x6a0
[<ffffffff810c88e0>] ? process_one_work+0x6a0/0x6a0
[<ffffffff810cf981>] kthread+0x101/0x120
[<ffffffff81104fb9>] ? trace_hardirqs_on_caller+0x129/0x1b0
[<ffffffff810cf880>] ? kthread_create_on_node+0x250/0x250
[<ffffffff81862a6f>] ret_from_fork+0x3f/0x70
[<ffffffff810cf880>] ? kthread_create_on_node+0x250/0x250

The warning that is tripped is

WARN_ON_ONCE(wait && current_is_async());

The module request is happening in an asynchronous thread
but the request is waiting. Switch to request_module_nowait
instead.

Fixes: 566079c849cf ("dm-mpath, scsi_dh: request scsi_dh modules in scsi_dh, not dm-mpath")
Reported-by: mustafa1024m@gmail.com
Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
---
Not actually tested, just an attempt at a patch from the backtrace
---
 drivers/scsi/scsi_dh.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_dh.c b/drivers/scsi/scsi_dh.c
index 0a2168e..5c945b4 100644
--- a/drivers/scsi/scsi_dh.c
+++ b/drivers/scsi/scsi_dh.c
@@ -111,7 +111,7 @@ static struct scsi_device_handler *scsi_dh_lookup(const char *name)
 
 	dh = __scsi_dh_lookup(name);
 	if (!dh) {
-		request_module("scsi_dh_%s", name);
+		request_module_nowait("scsi_dh_%s", name);
 		dh = __scsi_dh_lookup(name);
 	}
 
-- 
2.4.3