Messages in this thread | | | Subject | Re: [v2 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct | From | Yang Shi <> | Date | Sun, 1 Apr 2018 18:58:07 -0700 |
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On 3/26/18 11:29 PM, 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. > > 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.
Sorry for taking a little bit longer to get back since I was traveling. I think all the stuff can be protected by the new arg_lock except mm->brk since arg_lock can't prevent from concurrent writing from sys_brk().
We may use arg_lock to protect everything else other than mm->brk. The complexity sounds acceptable.
Of course, as Cyrill mentioned, he prefers to deprecating prctl_set_mm since C/R is the only user of it. We may wait until he is done?
Thanks, Yang
> > Thanks!
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