sched/fair: Fix unlocked reads of some cfs_b->quota/period

sched_cfs_period_timer() reads cfs_b->period without locks before calling
do_sched_cfs_period_timer(), and similarly unthrottle_offline_cfs_rqs()
would read cfs_b->period without the right lock. Thus a simultaneous
change of bandwidth could cause corruption on any platform where ktime_t
or u64 writes/reads are not atomic.

Extend cfs_b->lock from do_sched_cfs_period_timer() to include the read of
cfs_b->period to solve that issue; unthrottle_offline_cfs_rqs() can just
use 1 rather than the exact quota, much like distribute_cfs_runtime()
does.

There is also an unlocked read of cfs_b->runtime_expires, but a race
there would only delay runtime expiry by a tick. Still, the comparison
should just be != anyway, which clarifies even that problem.

Signed-off-by: Ben Segall <[email protected]>
Tested-by: Roman Gushchin <[email protected]>
[peterz: Fix compile warn]
Signed-off-by: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/20140519224945.20303.93530.stgit@sword-of-the-dawn.mtv.corp.google.com
Cc: [email protected]
Cc: Linus Torvalds <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>

0 files changed, 0 insertions, 0 deletions