Re: [PATCH] mm: do not call mem_cgroup_free() from within mem_cgroup_alloc()

[Michal Hocko]

On Fri 03-03-17 18:53:56, Tahsin Erdogan wrote:
> mem_cgroup_free() indirectly calls wb_domain_exit() which is not
> prepared to deal with a struct wb_domain object that hasn't executed
> wb_domain_init(). For instance, the following warning message is
> printed by lockdep if alloc_percpu() fails in mem_cgroup_alloc():
> 
>   INFO: trying to register non-static key.
>   the code is fine but needs lockdep annotation.
>   turning off the locking correctness validator.
>   CPU: 1 PID: 1950 Comm: mkdir Not tainted 4.10.0+ #151
>   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>   Call Trace:
>    dump_stack+0x67/0x99
>    register_lock_class+0x36d/0x540
>    __lock_acquire+0x7f/0x1a30
>    ? irq_work_queue+0x73/0x90
>    ? wake_up_klogd+0x36/0x40
>    ? console_unlock+0x45d/0x540
>    ? vprintk_emit+0x211/0x2e0
>    lock_acquire+0xcc/0x200
>    ? try_to_del_timer_sync+0x60/0x60
>    del_timer_sync+0x3c/0xc0
>    ? try_to_del_timer_sync+0x60/0x60
>    wb_domain_exit+0x14/0x20
>    mem_cgroup_free+0x14/0x40
>    mem_cgroup_css_alloc+0x3f9/0x620
>    cgroup_apply_control_enable+0x190/0x390
>    cgroup_mkdir+0x290/0x3d0
>    kernfs_iop_mkdir+0x58/0x80
>    vfs_mkdir+0x10e/0x1a0
>    SyS_mkdirat+0xa8/0xd0
>    SyS_mkdir+0x14/0x20
>    entry_SYSCALL_64_fastpath+0x18/0xad
> 
> Fix mem_cgroup_alloc() by doing more granular clean up in case of
> failures.
> 
> Fixes: 0b8f73e104285 ("mm: memcontrol: clean up alloc, online, offline, free functions")
> Signed-off-by: Tahsin Erdogan <tahsin@xxxxxxxxxx>

Please do not duplicate mem_cgroup_free code and rather add
__mem_cgroup_free which does everything except for wb_domain_exit.
An alternative would be to teach memcg_wb_domain_exit to not call
wb_domain_exit if it hasn't been initialized yet. The first option seems
easier.

Thanks!

> ---
>  mm/memcontrol.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index c52ec893e241..9a9d5630df91 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4194,9 +4194,12 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
>  	idr_replace(&mem_cgroup_idr, memcg, memcg->id.id);
>  	return memcg;
>  fail:
> +	for_each_node(node)
> +		free_mem_cgroup_per_node_info(memcg, node);
> +	free_percpu(memcg->stat);
>  	if (memcg->id.id > 0)
>  		idr_remove(&mem_cgroup_idr, memcg->id.id);
> -	mem_cgroup_free(memcg);
> +	kfree(memcg);
>  	return NULL;
>  }
>  
> -- 
> 2.12.0.rc1.440.g5b76565f74-goog
> 
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-- 
Michal Hocko
SUSE Labs