Date: Sat, 20 Feb 1999 12:17:40 -0500 (EST) From: Brian Feldman <green@unixhelp.org> To: current@freebsd.org Subject: More kernel threading ;) Message-ID: <Pine.BSF.4.05.9902201202140.23323-100000@janus.syracuse.net>
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This time I've got a problem with LinuxThreads (again), but really any kernel
threads. Anyway, for those who say to put your patches where your mouth is,
this is a pretty annoying problem which I have solved, and I've provided a
fix. So here goes:
With RFMEM, a shared address space is created and p->p_vmspace->vm_refcnt is
incremented. With shared memory, p->p_vmspace->vm_shm is allocated and used.
Now when processes exit (in the code before this patch), if vm_refcnt is not
1, shared memory is not taken care of at all. Instead, I changed it so that
shared memory's shm_nattch is decreased, and if < 1, freed. This solves the
problem of:
p1: fork1(RFMEM)
p[12]: shm create/attach
kill -9 p2 (no chance for the process to catch the signal and delete the
shared memory correctly)
exit1(p2)-> vm_refcnt--, shm not deleted/unreferenced
p1: no child! *SPLAT*
exit1(p1)-> vm_refcnt-- == 1, vm deleted and shm tried to be deleted:
shmexit-> shm all tried to be freed, but refcnt > 0, so it's not really deleted
and refcnt is dec'd once
You end up with (ipcs -a) a shared memory segment with a refcnt of 1, being
SET deleted but still there, and undeleteable because its' refcnt is 1 (refcnt
being shm_nattch...).
And the patch follows :)
--- src/sys/kern/sysv_shm.c.old Sat Feb 20 11:36:15 1999
+++ src/sys/kern/sysv_shm.c Sat Feb 20 11:46:19 1999
@@ -596,10 +596,13 @@
shmmap_s = (struct shmmap_state *)p->p_vmspace->vm_shm;
for (i = 0; i < shminfo.shmseg; i++, shmmap_s++)
- if (shmmap_s->shmid != -1)
+ if (shmmap_s->shmid != -1 &&
+ --shmsegs[IPCID_TO_IX(shmmap_s->shmid)].shm_nattch < 1)
shm_delete_mapping(p, shmmap_s);
- free((caddr_t)p->p_vmspace->vm_shm, M_SHM);
- p->p_vmspace->vm_shm = NULL;
+ if (p->p_vmspace->vm_refcnt == 1) {
+ free((caddr_t)p->p_vmspace->vm_shm, M_SHM);
+ p->p_vmspace->vm_shm = NULL;
+ }
}
void
--- src/sys/kern/kern_exit.c.old Sat Feb 20 11:36:02 1999
+++ src/sys/kern/kern_exit.c Sat Feb 20 11:46:22 1999
@@ -206,6 +206,10 @@
/* The next two chunks should probably be moved to vmspace_exit. */
vm = p->p_vmspace;
+
+ if (vm->vm_shm)
+ shmexit(p);
+
/*
* Release user portion of address space.
* This releases references to vnodes,
@@ -215,8 +219,6 @@
* may be mapped within that space also.
*/
if (vm->vm_refcnt == 1) {
- if (vm->vm_shm)
- shmexit(p);
pmap_remove_pages(vmspace_pmap(vm), VM_MIN_ADDRESS,
VM_MAXUSER_ADDRESS);
(void) vm_map_remove(&vm->vm_map, VM_MIN_ADDRESS,
Brian Feldman _ __ ___ ___ ___
green@unixhelp.org _ __ ___ | _ ) __| \
http://www.freebsd.org/ _ __ ___ ____ | _ \__ \ |) |
FreeBSD: The Power to Serve! _ __ ___ ____ _____ |___/___/___/
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