Description: f2fs: fix potential panic during fstrim
References:
Notes:
 carnil> Fixes 969d1b180d987c2be02de890d0fff0f66a0e80de (4.14-rc1) and
 carnil> as such we need to verify we have not backported the former.
Bugs:
upstream: released (4.14-rc5) [638164a2718f337ea224b747cf5977ef143166a4]
4.9-upstream-stable: N/A "Vulnerable code introduced later"
3.16-upstream-stable: N/A "Vulnerable code introduced later"
3.2-upstream-stable: N/A "Vulnerable code introduced later"
sid: N/A "Vulnerable code not present"
4.9-stretch-security: N/A "Vulnerable code not present"
3.16-jessie-security: N/A "Vulnerable code not present"
3.2-wheezy-security: N/A "Vulnerable code not present"