[lkml]   [2018]   [Mar]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [v2 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct

On 3/27/18 2:29 AM, Michal Hocko wrote:
> On Tue 27-03-18 02:20:39, Yang Shi wrote:
> [...]
> The patch looks reasonable to me. Maybe it would be better to be more
> explicit about the purpose of the patch. As others noticed, this alone
> wouldn't solve the mmap_sem contention issues. I _think_ that if you
> were more explicit about the mmap_sem abuse it would trigger less
> questions.

Yes, sure.

> I have just one more question. Now that you are touching this area,
> would you be willing to remove the following ugliness?
>> diff --git a/kernel/sys.c b/kernel/sys.c
>> index f2289de..17bddd2 100644
>> --- a/kernel/sys.c
>> +++ b/kernel/sys.c
>> @@ -1959,7 +1959,7 @@ static int prctl_set_mm_map(int opt, const void __user *addr, unsigned long data
>> return error;
>> }
>> - down_write(&mm->mmap_sem);
>> + down_read(&mm->mmap_sem);
> Why do we need to hold mmap_sem here and call find_vma, when only
> PR_SET_MM_ENV_END: is consuming it? I guess we can replace it wit the
> new lock and take the mmap_sem only for PR_SET_MM_ENV_END.

Actually, I didn't think of why. It looks prctl_set_mm() checks if vma
does exist when it tries to set stack_start, argv_* and env_*, btw not
only env_end.

Cyrill may be able to give us some hint since C/R is the main user of
this API.


> Thanks!

 \ /
  Last update: 2018-03-27 20:39    [W:0.174 / U:11.040 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site