Module Name: src
Committed By: martin
Date: Thu Oct 10 17:23:45 UTC 2019
Modified Files:
src/sys/kern [netbsd-9]: sysv_shm.c
Log Message:
Pull up following revision(s) (requested by chs in ticket #294):
sys/kern/sysv_shm.c: revision 1.140,1.141
revert rev 1.139 (fixing a race between shmat() and shmdt())
that approach turned out to be too complicated.
-
simpler fix for the race between shmat() and shmdt():
change shmat() to hold shm_lock until it is completely done.
To generate a diff of this commit:
cvs rdiff -u -r1.135.2.3 -r1.135.2.4 src/sys/kern/sysv_shm.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/sysv_shm.c
diff -u src/sys/kern/sysv_shm.c:1.135.2.3 src/sys/kern/sysv_shm.c:1.135.2.4
--- src/sys/kern/sysv_shm.c:1.135.2.3 Thu Oct 3 17:20:33 2019
+++ src/sys/kern/sysv_shm.c Thu Oct 10 17:23:45 2019
@@ -1,4 +1,4 @@
-/* $NetBSD: sysv_shm.c,v 1.135.2.3 2019/10/03 17:20:33 martin Exp $ */
+/* $NetBSD: sysv_shm.c,v 1.135.2.4 2019/10/10 17:23:45 martin Exp $ */
/*-
* Copyright (c) 1999, 2007 The NetBSD Foundation, Inc.
@@ -61,7 +61,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: sysv_shm.c,v 1.135.2.3 2019/10/03 17:20:33 martin Exp $");
+__KERNEL_RCSID(0, "$NetBSD: sysv_shm.c,v 1.135.2.4 2019/10/10 17:23:45 martin Exp $");
#ifdef _KERNEL_OPT
#include "opt_sysv.h"
@@ -87,7 +87,6 @@ struct shmmap_entry {
SLIST_ENTRY(shmmap_entry) next;
vaddr_t va;
int shmid;
- bool busy;
};
int shm_nused __cacheline_aligned;
@@ -314,10 +313,8 @@ sys_shmdt(struct lwp *l, const struct sy
struct uvm_object *uobj;
struct shmid_ds *shmseg;
size_t size;
- int segnum;
mutex_enter(&shm_lock);
-restart:
/* In case of reallocation, we will wait for completion */
while (__predict_false(shm_realloc_state))
cv_wait(&shm_realloc_cv, &shm_lock);
@@ -349,18 +346,12 @@ restart:
}
}
- segnum = IPCID_TO_IX(shmmap_se->shmid);
- if (shmmap_se->busy) {
- cv_wait(&shm_cv[segnum], &shm_lock);
- goto restart;
- }
-
SHMPRINTF(("shmdt: vm %p: remove %d @%lx\n",
p->p_vmspace, shmmap_se->shmid, shmmap_se->va));
/* Delete the entry from shm map */
uobj = shm_delete_mapping(shmmap_s, shmmap_se);
- shmseg = &shmsegs[segnum];
+ shmseg = &shmsegs[IPCID_TO_IX(shmmap_se->shmid)];
size = (shmseg->shm_segsz + PGOFSET) & ~PGOFSET;
mutex_exit(&shm_lock);
@@ -395,13 +386,10 @@ sys_shmat(struct lwp *l, const struct sy
vaddr_t attach_va;
vm_prot_t prot;
vsize_t size;
- int segnum;
/* Allocate a new map entry and set it */
shmmap_se = kmem_alloc(sizeof(struct shmmap_entry), KM_SLEEP);
shmmap_se->shmid = SCARG(uap, shmid);
- shmmap_se->busy = true;
- segnum = IPCID_TO_IX(shmmap_se->shmid);
mutex_enter(&shm_lock);
/* In case of reallocation, we will wait for completion */
@@ -449,44 +437,30 @@ sys_shmat(struct lwp *l, const struct sy
/*
* Create a map entry, add it to the list and increase the counters.
- * The lock will be dropped before the mapping, disable reallocation.
*/
shmmap_s = shmmap_getprivate(p);
SLIST_INSERT_HEAD(&shmmap_s->entries, shmmap_se, next);
shmmap_s->nitems++;
shmseg->shm_lpid = p->p_pid;
shmseg->shm_nattch++;
- shm_realloc_disable++;
/*
- * Add a reference to the uvm object while we hold the
- * shm_lock.
+ * Map the segment into the address space.
*/
uobj = shmseg->_shm_internal;
uao_reference(uobj);
- mutex_exit(&shm_lock);
-
- /*
- * Drop the shm_lock to map it into the address space, and lock
- * the memory, if needed (XXX where does this lock memory?).
- */
error = uvm_map(&vm->vm_map, &attach_va, size, uobj, 0, 0,
UVM_MAPFLAG(prot, prot, UVM_INH_SHARE, UVM_ADV_RANDOM, flags));
if (error)
goto err_detach;
/* Set the new address, and update the time */
- mutex_enter(&shm_lock);
shmmap_se->va = attach_va;
- shmmap_se->busy = false;
shmseg->shm_atime = time_second;
- shm_realloc_disable--;
retval[0] = attach_va;
SHMPRINTF(("shmat: vm %p: add %d @%lx\n",
p->p_vmspace, shmmap_se->shmid, attach_va));
- cv_broadcast(&shm_cv[segnum]);
err:
- cv_broadcast(&shm_realloc_cv);
mutex_exit(&shm_lock);
if (error && shmmap_se) {
kmem_free(shmmap_se, sizeof(struct shmmap_entry));
@@ -495,11 +469,7 @@ err:
err_detach:
uao_detach(uobj);
- mutex_enter(&shm_lock);
uobj = shm_delete_mapping(shmmap_s, shmmap_se);
- shm_realloc_disable--;
- cv_broadcast(&shm_cv[segnum]);
- cv_broadcast(&shm_realloc_cv);
mutex_exit(&shm_lock);
if (uobj != NULL) {
uao_detach(uobj);
