svn commit: r183750 - head/sys/kern
Warner Losh
imp at FreeBSD.org
Fri Oct 10 17:49:47 UTC 2008
Author: imp
Date: Fri Oct 10 17:49:47 2008
New Revision: 183750
URL: http://svn.freebsd.org/changeset/base/183750
Log:
Close, but not eliminate, a race condition. It is one that properly
designed drivers would never hit, but was exposed in diving into
another problem...
When expanding the devclass array, free the old memory after updating
the pointer to the new memory. For the following single race case,
this helps:
allocate new memory
copy to new memory
free old memory
<interrupt> read pointer to freed memory
update pointer to new memory
Now we do
allocate new memory
copy to new memory
update pointer to new memory
free old memory
Which closes this problem, but doesn't even begin to address the
multicpu races, which all should be covered by Giant at the moment,
but likely aren't completely.
Note: reviewers were ok with this fix, but suggested the use case
wasn't one we wanted to encourage.
Reviewed by: jhb, scottl.
Modified:
head/sys/kern/subr_bus.c
Modified: head/sys/kern/subr_bus.c
==============================================================================
--- head/sys/kern/subr_bus.c Fri Oct 10 17:48:39 2008 (r183749)
+++ head/sys/kern/subr_bus.c Fri Oct 10 17:49:47 2008 (r183750)
@@ -1344,20 +1344,22 @@ devclass_alloc_unit(devclass_t dc, int *
* this one.
*/
if (unit >= dc->maxunit) {
- device_t *newlist;
+ device_t *newlist, *oldlist;
int newsize;
+ oldlist = dc->devices;
newsize = roundup((unit + 1), MINALLOCSIZE / sizeof(device_t));
newlist = malloc(sizeof(device_t) * newsize, M_BUS, M_NOWAIT);
if (!newlist)
return (ENOMEM);
- bcopy(dc->devices, newlist, sizeof(device_t) * dc->maxunit);
+ if (oldlist != NULL)
+ bcopy(oldlist, newlist, sizeof(device_t) * dc->maxunit);
bzero(newlist + dc->maxunit,
sizeof(device_t) * (newsize - dc->maxunit));
- if (dc->devices)
- free(dc->devices, M_BUS);
dc->devices = newlist;
dc->maxunit = newsize;
+ if (oldlist != NULL)
+ free(oldlist, M_BUS);
}
PDEBUG(("now: unit %d in devclass %s", unit, DEVCLANAME(dc)));
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