arm/185046: [armv6] issues with dhclient/sshd and jemalloc on raspberry pi and others

[Adrian Chadd]

>Number:         185046
>Category:       arm
>Synopsis:       [armv6] issues with dhclient/sshd and jemalloc on raspberry pi and others
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-arm
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Fri Dec 20 20:40:00 UTC 2013
>Closed-Date:
>Last-Modified:
>Originator:     Adrian Chadd
>Release:        
>Organization:
>Environment:
>Description:
There's been issues with sshd/dhclient being very upset.

It was traced down to some jemalloc behaviour with processes that fork and do.. stuff. I'm not going to pretend to know exactly what the errnat behaviour was; it's likely lurking in the freebsd-arm mailing lists.

It was bisected down to this commit:

http://svnweb.freebsd.org/base/head/sys/arm/arm/pmap-v6.c?r1=251370&r2=252694&pathrev=252694

Reverting this apparently fixes the issue.

>From the committer of the change:

> I guess it should be some performance impact since we will need to
> write all pages marked as RW to backing
> storage on page-out. This is regardless of its actual dirty state (no
> modified emulation).
> But this was how it behaved earlier and nothing bad happened so it
> might be worth to temporary revert it and
> debug the problem without the negative influence on the users. After
> proper fix we should apply it again.
>
> It's up to you. I have no objections to that (I have few other patches
> that need to wait for pmap problems
> resolution anyway like pmap_copy() + SP).

>How-To-Repeat:

>Fix:


>Release-Note:
>Audit-Trail:
>Unformatted: