Description: bcache: fix potential deadlock problem in btree_gc_coalesce
References:
 https://lkml.org/lkml/2020/4/26/87
Notes:
Bugs:
upstream: released (5.8-rc2) [be23e837333a914df3f24bf0b32e87b0331ab8d1]
4.19-upstream-stable: released (4.19.130) [2ee8f6e72269eb06649ebab3da6bbf59aed3eabe]
4.9-upstream-stable: released (4.9.229) [be676835b2250861d525b8e2a8e2bed8c1a9027d]
3.16-upstream-stable: ignored "EOL"
sid: released (5.7.6-1)
4.19-buster-security: released (4.19.131-1)
4.9-stretch-security: released (4.9.240-1)
3.16-jessie-security: ignored "EOL"