I have exactly the same problem. Steam error log shows malloc: unknown:0: assertion botched free: called with unallocated block argument
for the games that do not running using "optirun steam" or editing the launch settings for each game. I've not tried downgrading to an older version of the libdrm intel package however as editing the shell script for each game to run optirun prior to the ${DEBUGGER} arg seems to also work. Not an ideal solution but it saves downgrading a package. I'm running Debian Jessie with a Geforce 850M and optimus using bumblebee and either optirun or primusrun. I also have the same libdrm-intel package version installed as the OP. Regards, Gary
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