Re: [patch]mm: fix a memcg warning

[Michal Hocko <mhocko@suse.cz>]

On Mon 01-08-11 14:41:18, Shaohua Li wrote:
> I get below warning:
> BUG: using smp_processor_id() in preemptible [00000000] code: bash/739
> caller is drain_local_stock+0x1a/0x55
> Pid: 739, comm: bash Tainted: G        W   3.0.0+ #255
> Call Trace:
>  [<ffffffff813435c6>] debug_smp_processor_id+0xc2/0xdc
>  [<ffffffff8114ae9b>] drain_local_stock+0x1a/0x55
>  [<ffffffff8114b076>] drain_all_stock+0x98/0x13a
>  [<ffffffff8114f04c>] mem_cgroup_force_empty+0xa3/0x27a
>  [<ffffffff8114ff1d>] ? sys_close+0x38/0x138
>  [<ffffffff811a7631>] ? environ_read+0x1d/0x159
>  [<ffffffff8114f253>] mem_cgroup_force_empty_write+0x17/0x19
>  [<ffffffff810c72fb>] cgroup_file_write+0xa8/0xba
>  [<ffffffff811522ce>] vfs_write+0xb3/0x138
>  [<ffffffff81152416>] sys_write+0x4a/0x71
>  [<ffffffff8114ffd5>] ? sys_close+0xf0/0x138
>  [<ffffffff8176deab>] system_call_fastpath+0x16/0x1b
> 
> drain_local_stock() should be run with preempt disabled.

Ahh, yes. This got in with d1a05b69 (memcg: do not try to drain per-cpu
caches without pages) which started calling drain_local_stock directly
rather than from a kernel thread.

> Signed-off-by: Shaohua Li <shaohua.li@intel.com>

Acked-by: Michal Hocko <mhocko@suse.cz>

Thanks for catching this.

> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 5f84d23..11d5671 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2169,13 +2169,7 @@ static void drain_all_stock(struct mem_cgroup *root_mem, bool sync)
>  
>  	/* Notify other cpus that system-wide "drain" is running */
>  	get_online_cpus();
> -	/*
> -	 * Get a hint for avoiding draining charges on the current cpu,
> -	 * which must be exhausted by our charging.  It is not required that
> -	 * this be a precise check, so we use raw_smp_processor_id() instead of
> -	 * getcpu()/putcpu().
> -	 */
> -	curcpu = raw_smp_processor_id();
> +	curcpu = get_cpu();
>  	for_each_online_cpu(cpu) {
>  		struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu);
>  		struct mem_cgroup *mem;
> @@ -2192,6 +2186,7 @@ static void drain_all_stock(struct mem_cgroup *root_mem, bool sync)
>  				schedule_work_on(cpu, &stock->work);
>  		}
>  	}
> +	put_cpu();
>  
>  	if (!sync)
>  		goto out;
> 
> 
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-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

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