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simpler fix for the race between shmat() and shmdt(): 

change shmat() to hold shm_lock until it is completely done.
This commit is contained in:
chs 2019-10-09 17:47:13 +00:00
parent a851cc5747
commit cf529c6de1
1 changed files with 3 additions and 18 deletions
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21
sys/kern/sysv_shm.c
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@ -1,4 +1,4 @@
/* $NetBSD: sysv_shm.c,v 1.140 2019/10/09 17:44:45 chs Exp $ */
/* $NetBSD: sysv_shm.c,v 1.141 2019/10/09 17:47:13 chs 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 1.140 2019/10/09 17:44:45 chs Exp $");
__KERNEL_RCSID(0, "$NetBSD: sysv_shm.c,v 1.141 2019/10/09 17:47:13 chs Exp $");
#ifdef _KERNEL_OPT
#include "opt_sysv.h"
@ -437,42 +437,30 @@ sys_shmat(struct lwp *l, const struct sys_shmat_args *uap, register_t *retval)
/*
* 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;
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));
err:
cv_broadcast(&shm_realloc_cv);
mutex_exit(&shm_lock);
if (error && shmmap_se) {
kmem_free(shmmap_se, sizeof(struct shmmap_entry));
@ -481,10 +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_realloc_cv);
mutex_exit(&shm_lock);
if (uobj != NULL) {
uao_detach(uobj);