[src/netbsd-9]: src/sys/kern Pull up following revision(s) (requested by chs ...

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

details:   https://anonhg.NetBSD.org/src/rev/3324fe4f8a3d
branches:  netbsd-9
changeset: 462628:3324fe4f8a3d
user:      martin <martin%NetBSD.org@localhost>
date:      Thu Oct 10 17:23:45 2019 +0000

description:
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.

diffstat:

 sys/kern/sysv_shm.c |  38 ++++----------------------------------
 1 files changed, 4 insertions(+), 34 deletions(-)

diffs (129 lines):

diff -r 5ba4d320fab4 -r 3324fe4f8a3d sys/kern/sysv_shm.c
--- a/sys/kern/sysv_shm.c       Tue Oct 08 17:06:28 2019 +0000
+++ b/sys/kern/sysv_shm.c       Thu Oct 10 17:23:45 2019 +0000
@@ -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 @@
        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 */
@@ -449,44 +437,30 @@
 
        /*
         * 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_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);