PR/41374 CVS commit: src/sys

[YAMAMOTO Takashi <yamt%netbsd.org@localhost>]

The following reply was made to PR kern/41374; it has been noted by GNATS.

From: YAMAMOTO Takashi <yamt%netbsd.org@localhost>
To: gnats-bugs%gnats.NetBSD.org@localhost
Cc: 
Subject: PR/41374 CVS commit: src/sys
Date: Sat, 16 May 2009 08:29:54 +0000

 Module Name:   src
 Committed By:  yamt
 Date:          Sat May 16 08:29:54 UTC 2009
 
 Modified Files:
        src/sys/kern: vfs_subr.c
        src/sys/sys: vnode.h
 
 Log Message:
 put a flag bit into v_usecount to prevent vtryget during getcleanvnode.
 this fixes the following deadlock.
 
        a thread doing getcleanvnode:
        pick a vnode
        acqure v_interlock
        v_usecount++
        call vclean
 
                now, another thread doing cache_lookup:
                picks the vnode
                vtryget succeed
                vn_lock succeed
 
        now in vclean:
        set VI_XLOCK (too late to be noticed by the competing thread)
        wait on the vnode lock (this might violate locking order)
 
 the use of a flag bit was suggested by Andrew Doran.  PR/41374.
 
 
 To generate a diff of this commit:
 cvs rdiff -u -r1.378 -r1.379 src/sys/kern/vfs_subr.c
 cvs rdiff -u -r1.206 -r1.207 src/sys/sys/vnode.h
 
 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.