[OpenAFS-devel] OpenAFS + openMosix
Onime Clement
onime@ictp.trieste.it
Tue, 3 Dec 2002 10:35:27 +0100 (MET)
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Subject: OpenAFS + OpenMosix
I seem to have discovered a bug in the OpenAFS kernel module code that
causes linux to fail when using the OpenMosix kernel.
This problem was reported earlier this year with previous openafs and
openmosix versions.
OpenAFS version 1.2.7
OpenMosix kernel version 2.4.18-openmosix3
RedHat Linux 7.3
Symptoms:
=========
When running on an openmosix kernel. Some applications
that tries to close files that were opened using the mmap call runs into
problems. The application hangs, it is impossible to kill the application,
impossible to run top, ps or kill or any other proc base utility.
Although the computer is still usable, it is also impossible to halt or
reboot the machine via software. Only a hard reset works or power off works.
How to reproduce:
=================
It is possible to reproduce the problem by trying to run netscape or staroffice
5.2 when your home directory is in AFS, on a machine running an OpenMosix
kernel.
Analysis:
=========
I traced the code to the routine afs_linux_vma_close in the osi_vnodeops.c file
And particularly the afs_close call
Preliminary tracing using printk indicates that the sometimes calls to
afs_close in the function does not return.
Specifically when afs_close is called with vcp->execsOrWriters > 0 , it blocks
which causes the hanging.
patch:
======
A simple patch to osi_vnodeops.c to fix this problem is included below and
attached to this mail.
The patch needs to be applied from the src directory or with the right patch
-p option.
Thanks
Clement Onime
System and Network Analyst
The Abdus Salam ICTP
Trieste, Italy
<--------------------- cut here --------------------->
--- afs/osi_vnodeops.c.orig Thu Aug 1 21:12:01 2002
+++ afs/osi_vnodeops.c Tue Dec 3 09:43:21 2002
@@ -342,12 +342,26 @@
if (vcp->mapcnt) {
vcp->mapcnt--;
+ if (vcp->mapcnt == 0) {
+ /* This bit is supposed to undo what was
+ * done on lines */
+ if (vcp->execsOrWriters > 0)
+ vcp->execsOrWriters--;
+ if (vcp->opens > 0)
+ vcp->opens--;
+ /* vcp->states &= ~CMAPPED; */
+ }
ReleaseWriteLock(&vcp->lock);
if (!vcp->mapcnt) {
credp = crref();
- (void) afs_close(vcp, vmap->vm_file->f_flags, credp);
+ /* printk("AFSMM: afs_close: Mapcnt=%d Opens=%d execsOrWriters=%d\n", vcp->mapcnt, vcp->opens, vcp->execsOrWriters); */
+ /* It appears afs_close blocks if called when execsOrWriters > 0 */
+ if (vcp->execsOrWriters == 0)
+ (void) afs_close(vcp, vmap->vm_file->f_flags, credp);
/* only decrement the execsOrWriters flag if this is not a writable
* file. */
+ /* Why the limitation here */
if (! (vmap->vm_file->f_flags & (FWRITE | FTRUNC)))
- vcp->execsOrWriters--;
+ if (vcp->execsOrWriters > 0)
+ vcp->execsOrWriters--;
vcp->states &= ~CMAPPED;
@@ -398,6 +412,10 @@
}
+
if (code == 0) {
ObtainWriteLock(&vcp->lock,531);
+ /* Add an open reference on the first mapping. */
+ if (vcp->mapcnt == 0) {
+ /* Only for the first time */
/* Set out vma ops so we catch the close. The following test should be
* the same as used in generic_file_mmap.
@@ -420,7 +438,5 @@
}
-
- /* Add an open reference on the first mapping. */
- if (vcp->mapcnt == 0) {
+ /*These variables get set when mapcnt == 0 */
vcp->execsOrWriters++;
vcp->opens++;
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