https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=260347
Bug ID: 260347
Summary: after kldunload memory allocated by the module stays
wired
Product: Base System
Version: 13.0-RELEASE
Hardware: amd64
OS: Any
Status: New
Severity: Affects Many People
Priority: ---
Component: kern
Assignee: [email protected]
Reporter: [email protected]
I have a very simple kernel module, textbook example, that uses static buffer.
It seems memory stays wired even if module is unloaded. If I do it enough times
system runs out of memory. Not reproducible on FreeBSD 12.2 amd64.
I'm opening the PR based on the forums discussion:
https://forums.freebsd.org/threads/kldunload-failed-to-release-memory.83286/
I don't agree with the replies there (mine are _martin); if I'm mistaken I
apologies for wasting everybody's time (and will rethink opening PR in the
future).
Simple kernel module:
/*
* KLD Skeleton
* Inspired by Andrew Reiter's Daemonnews article
*/
#include <sys/types.h>
#include <sys/module.h>
#include <sys/systm.h> /* uprintf */
#include <sys/errno.h>
#include <sys/param.h> /* defines used in kernel.h */
#include <sys/kernel.h> /* types used in module initialization */
#define BUFFER_SIZE 10*1000*1024 // 10 MB
static char gBuffer[BUFFER_SIZE];
static int demo_init (void)
{
for (int i=0; i<BUFFER_SIZE; i++)
{
gBuffer[i] = 'A';
}
return 0;
}
static void demo_exit (void)
{
for (int i=0; i<BUFFER_SIZE; i++)
{
gBuffer[i] += 1;
}
}
/*
* Load handler that deals with the loading and unloading of a KLD.
*/
static int
skel_loader(struct module *m, int what, void *arg)
{
int err = 0;
switch (what) {
case MOD_LOAD: /* kldload */
uprintf("Skeleton KLD loaded.\n");
demo_init();
break;
case MOD_UNLOAD:
uprintf("Skeleton KLD unloaded.\n");
demo_exit();
break;
default:
err = EOPNOTSUPP;
break;
}
return(err);
}
/* Declare this module to the rest of the kernel */
static moduledata_t skel_mod = {
"skel",
skel_loader,
NULL
};
DECLARE_MODULE(skeleton, skel_mod, SI_SUB_KLD, SI_ORDER_ANY);
Makefile:
SRCS=skeleton.c
KMOD=skeleton
.include <bsd.kmod.mk>
I compile the module and test it with the loop:
sh
while true ; do kldload ./test.ko && kldunload ./test.ko ; done
In the other terminal I watch the memory utilization with top. Wired memory
increases to the point where system freezes. OOM killer kills processes and
system is available after a while. If I relaunch the top again I see wired
memory is still almost all used, as if module leaves memory leak.
This behavior is not reproducible on FreeBSD 12.2 as I mentioned above.
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