Description: __blk_add_trace use-after-free 
References:
 https://bugzilla.kernel.org/show_bug.cgi?id=205711
Notes:
 bwh> Needs additional fix, commit 153031a301bb "blktrace: fix dereference
 bwh> after null check".
Bugs:
upstream: released (5.6-rc4) [c780e86dd48ef6467a1146cf7d0fe1e05a635039]
4.19-upstream-stable: released (4.19.119) [473d7f5ed75b8c3750f0c6b442c8e23090d6da8f]
4.9-upstream-stable: released (4.9.224) [284dba674c063ac5cab9ffc1ea07f7b199aeb62f]
3.16-upstream-stable: released (3.16.83) [4398bce1bdf258f7d67bcc38c46f5fa9546448bd]
sid: released (5.5.13-1)
4.19-buster-security: released (4.19.118-1) [bugfix/all/blktrace-protect-q-blk_trace-with-rcu.patch]
4.9-stretch-security: released (4.9.210-1+deb9u1) [bugfix/all/blktrace-protect-q-blk_trace-with-rcu.patch]
3.16-jessie-security: released (3.16.84-1)