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SubjectRe: memory-controller patch fails to boot in qemu [mmotm]
* Hugh Dickins <hugh.dickins@tiscali.co.uk> [2009-08-01 23:09:09]:

> I've just finished chasing something similar (without qemu),
> and was about to post this:
>
> [PATCH mmotm] memory controller: soft limit organize cgroups v9 fix
>
> CONFIG_CGROUP_MEM_RES_CTLR=y CONFIG_PREEMPT=y mmotm fails to boot:
> Kernel panic - not syncing: No init found; after lots of scheduling
> while atomics, starting from when async_thread does sd_probe_async.
>
> mem_cgroup_soft_limit_check() was doing an unbalanced get_cpu():
> don't get_cpu if we won't need it, and put_cpu if we did get_cpu.
>
> Hmm, this a weird function, passed an argument just to tell it to do
> nothing. Perhaps a placeholder for something more sensible to come?
>
> Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
> ---
> Fix to memory-controller-soft-limit-organize-cgroups-v9.patch
>
> mm/memcontrol.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> --- mmotm/mm/memcontrol.c 2009-08-01 05:48:08.000000000 +0100
> +++ linux/mm/memcontrol.c 2009-08-01 21:45:37.000000000 +0100
> @@ -375,19 +375,21 @@ static bool mem_cgroup_soft_limit_check(
> bool over_soft_limit)
> {
> bool ret = false;
> - int cpu = get_cpu();
> + int cpu;
> s64 val;
> struct mem_cgroup_stat_cpu *cpustat;
>
> if (!over_soft_limit)
> return ret;
>
> + cpu = get_cpu();
> cpustat = &mem->stat.cpustat[cpu];
> val = __mem_cgroup_stat_read_local(cpustat, MEM_CGROUP_STAT_EVENTS);
> if (unlikely(val > SOFTLIMIT_EVENTS_THRESH)) {
> __mem_cgroup_stat_reset_safe(cpustat, MEM_CGROUP_STAT_EVENTS);
> ret = true;
> }
> + put_cpu();
> return ret;
> }
>

I can confirm that this fixes the problem with CONFIG_PREEMPT enabled.

Tested-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>


--
Balbir


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