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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