Description: block, bfq: fix use-after-free in bfq_idle_slice_timer_body
References:
 https://patchwork.kernel.org/patch/11447049/
Notes:
 bwh> bfq scheduler was added in 4.12
Bugs:
upstream: released (5.7-rc1) [2f95fa5c955d0a9987ffdc3a095e2f4e62c5f2a9]
4.19-upstream-stable: released (4.19.116) [d999063be0cf91bff8e0d6daaea21e1a4f70d336]
4.9-upstream-stable: N/A "Vulnerable code not present"
3.16-upstream-stable: N/A "Vulnerable code not present"
sid: released (5.6.7-1)
4.19-buster-security: released (4.19.118-1)
4.9-stretch-security: N/A "Vulnerable code not present"
3.16-jessie-security: N/A "Vulnerable code not present"