kern/84318: non-atomic operations on vfs.runningbufspace
Ade Lovett
ade at FreeBSD.org
Fri Jul 29 18:50:09 GMT 2005
>Number: 84318
>Category: kern
>Synopsis: non-atomic operations on vfs.runningbufspace
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Fri Jul 29 18:50:08 GMT 2005
>Closed-Date:
>Last-Modified:
>Originator: Ade Lovett
>Release: FreeBSD 6.0-BETA1 i386
>Organization:
Supernews
>Environment:
FreeBSD 6.0-BETA1 #0: Wed Jul 27 17:52:15 UTC 2005 root at builder.supernews.net:/usr/obj/usr/src/sys/SUPERNEWS
6.0-BETA1 as of date above, affects all architectures
>Description:
There are two locations within /sys/vm/vnode_pager.c where
non-atomic operations are used on runningbufspace, resulting
in cases where this value can go negative with various
undefined and interesting results.
>How-To-Repeat:
Run a 6.0 system under heavy VFS load (in our case, as a
Usenet news transit server). Monitor the vfs.runningbufspace
sysctl, and after a short period (30 to 60 minutes is usual),
notice that:
transit-12# sysctl vfs.runningbufspace
vfs.runningbufspace: -131072
>Fix:
Apply following to /sys/vm/vnode_pager.c which corrects the
two locations where non-atomic operations are being used
to modify runningbufspace.
Index: vnode_pager.c
===================================================================
RCS file: /home/FreeBSD/cvs/src/sys/vm/vnode_pager.c,v
retrieving revision 1.221
diff -u -1 -r1.221 vnode_pager.c
--- vnode_pager.c 19 May 2005 03:53:07 -0000 1.221
+++ vnode_pager.c 28 Jul 2005 21:58:24 -0000
@@ -66,2 +66,3 @@
#include <sys/sf_buf.h>
+#include <sys/mutex.h>
@@ -548,3 +549,3 @@
bp->b_runningbufspace = bp->b_bufsize;
- runningbufspace += bp->b_runningbufspace;
+ atomic_add_int(&runningbufspace, bp->b_runningbufspace);
@@ -900,3 +901,3 @@
bp->b_runningbufspace = bp->b_bufsize;
- runningbufspace += bp->b_runningbufspace;
+ atomic_add_int(&runningbufspace, bp->b_runningbufspace);
>Release-Note:
>Audit-Trail:
>Unformatted:
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