Re: [v3 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct

[Yang Shi <yang.shi@linux.alibaba.com>]

On 4/10/18 5:28 AM, Cyrill Gorcunov wrote:
> On Tue, Apr 10, 2018 at 01:10:01PM +0200, Michal Hocko wrote:
>>> Because do_brk does vma manipulations, for this reason it's
>>> running under down_write_killable(&mm->mmap_sem). Or you
>>> mean something else?
>> Yes, all we need the new lock for is to get a consistent view on brk
>> values. I am simply asking whether there is something fundamentally
>> wrong by doing the update inside the new lock while keeping the original
>> mmap_sem locking in the brk path. That would allow us to drop the
>> mmap_sem lock in the proc path when looking at brk values.
> Michal gimme some time. I guess  we might do so, but I need some
> spare time to take more precise look into the code, hopefully today
> evening. Also I've a suspicion that we've wracked check_data_rlimit
> with this new lock in prctl. Need to verify it again.

I see you guys points. We might be able to move the drop of mmap_sem 
before setting mm->brk in sys_brk since mmap_sem should be used to 
protect vma manipulation only, then protect the value modify with the 
new arg_lock. Then we can eliminate mmap_sem stuff in prctl path, and it 
also prevents from wrecking check_data_rlimit.

At the first glance, it looks feasible to me. Will look into deeper later.

Thanks,
Yang