BugLink: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1773410
BugLink: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1777850

Kernel panic is observed when network manager is stopped or Interface is
is DOWN, while system is entering into hibernation. The root cause of the
issue is scan work function keeps running even after cancel_hw_scan() call.
Issue is resolved by calling cancel_work_sync().

...skipping...
[ 1171.913244] BUG: unable to handle page request at 00000000001067e38
[ 1171.913248] IP: cfg80211_scan_done+0xb0/0xc0 [cfg80211]
[ 1171.913554] Hardware name: Dell Inc. Edge Gateway 3003/      , BIOS 01.00.06 01/22/2018
[ 1171.913668] Workqueue: phy1 ieee80211_scan_work [mac80211]
[ 1171.913773] RIP: 0010:cfg80211_scan_done+0xb0/0xc0 [cfg80211]
[ 1171.913780] RSP: 0018:ffffc1fe41b47dc8 EFLAGS: 00010286
[ 1171.913789] RAX: 0000000000000001 RBX: ffffffffc0e60120 RCX: 0000000100080006
[ 1171.913794] RDX: ffff9eeab7e3bc58 RSI: ffff9eeab0c69080 RDI: ffff9eeab7e3bc00
[ 1171.913799] RBP: ffff9eeab7e3bc00 R08: 00000000b7e3b201 R09: 0000000100080006
[ 1171.913805] R10: ffffc1fe41b47d20 R11: 0000000000000000 R12: ffff9eeab0c69080
[ 1171.913810] R13: 0000000000000022 R14: ffff9eeab0c68760 R15: ffff9eeab7af3c00
[ 1171.913817] FS:  0000000000000000(0000) GS:ffff9eeab0000000(0000) knlGS:0000000000000000
[ 1171.913823] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1171.913828] CR2: 00007f76c73ac190 CR3: 000000006e20a000 CR4: 00000000001006f0
[ 1171.913833] Call Trace:
[ 1171.913864]  ? rsi_mac80211_sta_remove+0x260/0x260 [rsi_91x]
[ 1171.913971]  __ieee80211_scan_completed+0xb1/0x390 [mac80211]
[ 1171.914078]  ieee80211_scan_work+0x7e/0x480 [mac80211]
[ 1171.914098]  process_one_work+0x142/0x3d0
[ 1171.914111]  worker_thread+0x229/0x440
[ 1171.914122]  kthread+0xf5/0x130
[ 1171.914132]  ? process_one_work+0x3d0/0x3d0
[ 1171.914140]  ? kthread_associate_blkcg+0x90/0x90
[ 1171.914152]  ret_from_fork+0x35/0x40
Signed-off-by: Siva Rebbagondla <siva.rebbagondla@redpinesignals.com>
Acked-by: Anthony Wong <anthony.wong@canonical.com>
Acked-by: Shrirang Bagul <shrirang.bagul@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>