https://github.com/torvalds/linux
Revision 2e084786f6fe052274f1dfa7c675fe4a02cacd6e authored by Lai Jiangshan on 12 June 2008, 08:42:58 UTC, committed by Ingo Molnar on 12 June 2008, 12:23:55 UTC
I found a bug which can be reproduced by this way:(linux-2.6.26-rc5, x86-64) (use 2^32, 2^33, ...., 2^63 as shares value) # mkdir /dev/cpuctl # mount -t cgroup -o cpu cpuctl /dev/cpuctl # cd /dev/cpuctl # mkdir sub # echo 0x8000000000000000 > sub/cpu.shares # echo $$ > sub/tasks oops here! divide by zero. This is because do_div() expects the 2th parameter to be 32 bits, but unsigned long is 64 bits in x86_64. Peter Zijstra pointed it out that the sane thing to do is limit the shares value to something smaller instead of using an even more expensive divide. Also, I found another bug about "the shares value is too large": pid1 and pid2 are set affinity to cpu#0 pid1 is attached to cg1 and pid2 is attached to cg2 if cg1/cpu.shares = 1024 cg2/cpu.shares = 2000000000 then pid2 got 100% usage of cpu, and pid1 0% if cg1/cpu.shares = 1024 cg2/cpu.shares = 20000000000 then pid2 got 0% usage of cpu, and pid1 100% And a weight of a cfs_rq is the sum of weights of which entities are queued on this cfs_rq, so the shares value should be limited to a smaller value. I think that (1UL << 18) is a good limited value: 1) it's not too large, we can create a lot of group before overflow 2) it's several times the weight value for nice=-19 (not too small) Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
1 parent 16882c1
Tip revision: 2e084786f6fe052274f1dfa7c675fe4a02cacd6e authored by Lai Jiangshan on 12 June 2008, 08:42:58 UTC
sched: fair group: fix overflow(was: fix divide by zero)
sched: fair group: fix overflow(was: fix divide by zero)
Tip revision: 2e08478
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drivers | ||
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COPYING | -rw-r--r-- | 18.3 KB |
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Kbuild | -rw-r--r-- | 2.4 KB |
MAINTAINERS | -rw-r--r-- | 98.3 KB |
Makefile | -rw-r--r-- | 53.8 KB |
README | -rw-r--r-- | 16.5 KB |
REPORTING-BUGS | -rw-r--r-- | 3.1 KB |
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