kern/44763: select/poll direct-set optimization seems racy

[yamt%NetBSD.org@localhost]

>Number:         44763
>Category:       kern
>Synopsis:       select/poll direct-set optimization seems racy
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Mar 24 07:05:00 +0000 2011
>Originator:     YAMAMOTO Takashi
>Release:        NetBSD current
>Organization:
        
>Environment:
        
        
System: NetBSD current
Architecture: i386
Machine: i386
>Description:
        select/poll direct-set optimization seems racy.

        - there is a race between sel_setevents and pollscan/selscan wrt
          ofds bits/revents updates.  thus l_selret is inaccurate.
        - sel_setevents can increase l_selret more than desirable if selnotify
          is called again and again quickly enough
>How-To-Repeat:
        run regress/sys/kern/select
>Fix:
        a workaround: NO_DIRECT_SELECT

>Unformatted: