[src/trunk]: src/sys/kern revert rev 1.139 (fixing a race between shmat() and...

[chs <chs%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/b6f06534ec43
branches:  trunk
changeset: 965998:b6f06534ec43
user:      chs <chs%NetBSD.org@localhost>
date:      Wed Oct 09 17:44:45 2019 +0000

description:
revert rev 1.139 (fixing a race between shmat() and shmdt())
that approach turned out to be too complicated.

diffstat:

 sys/kern/sysv_shm.c |  21 +++------------------
 1 files changed, 3 insertions(+), 18 deletions(-)

diffs (93 lines):

diff -r 6e5800f03989 -r b6f06534ec43 sys/kern/sysv_shm.c
--- a/sys/kern/sysv_shm.c       Wed Oct 09 17:28:46 2019 +0000
+++ b/sys/kern/sysv_shm.c       Wed Oct 09 17:44:45 2019 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: sysv_shm.c,v 1.139 2019/10/01 16:36:58 chs Exp $       */
+/*     $NetBSD: sysv_shm.c,v 1.140 2019/10/09 17:44:45 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 1.139 2019/10/01 16:36:58 chs Exp $");
+__KERNEL_RCSID(0, "$NetBSD: sysv_shm.c,v 1.140 2019/10/09 17:44:45 chs Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_sysv.h"
@@ -87,7 +87,6 @@
        SLIST_ENTRY(shmmap_entry) next;
        vaddr_t va;
        int shmid;
-       bool busy;
 };
 
 int                    shm_nused               __cacheline_aligned;
@@ -314,10 +313,8 @@
        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 @@
                }
        }
 
-       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 @@
        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 */
@@ -478,13 +466,11 @@
        /* 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);
@@ -498,7 +484,6 @@
        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) {