Author: kib
Date: Wed Feb 18 18:12:06 2015
New Revision: 278963
URL: https://svnweb.freebsd.org/changeset/base/278963
Log:
If malloc() sleeps, Giant is dropped. Recheck for another thread
doing our work.
Remove unneeded check for failed M_WAITOK allocation.
Reviewed by: alc
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Modified:
head/sys/kern/sysv_shm.c
Modified: head/sys/kern/sysv_shm.c
==============================================================================
--- head/sys/kern/sysv_shm.c Wed Feb 18 17:28:55 2015 (r278962)
+++ head/sys/kern/sysv_shm.c Wed Feb 18 18:12:06 2015 (r278963)
@@ -358,9 +358,22 @@ kern_shmat(td, shmid, shmaddr, shmflg)
if (shmmap_s == NULL) {
shmmap_s = malloc(shminfo.shmseg * sizeof(struct shmmap_state),
M_SHM, M_WAITOK);
- for (i = 0; i < shminfo.shmseg; i++)
- shmmap_s[i].shmid = -1;
- p->p_vmspace->vm_shm = shmmap_s;
+
+ /*
+ * If malloc() above sleeps, the Giant lock is
+ * temporarily dropped, which allows another thread to
+ * allocate shmmap_state and set vm_shm. Recheck
+ * vm_shm and free the new shmmap_state if another one
+ * is already allocated.
+ */
+ if (p->p_vmspace->vm_shm != NULL) {
+ free(shmmap_s, M_SHM);
+ shmmap_s = p->p_vmspace->vm_shm;
+ } else {
+ for (i = 0; i < shminfo.shmseg; i++)
+ shmmap_s[i].shmid = -1;
+ p->p_vmspace->vm_shm = shmmap_s;
+ }
}
shmseg = shm_find_segment_by_shmid(shmid);
if (shmseg == NULL) {
@@ -826,8 +839,6 @@ shmrealloc(void)
return;
newsegs = malloc(shminfo.shmmni * sizeof(*newsegs), M_SHM, M_WAITOK);
- if (newsegs == NULL)
- return;
for (i = 0; i < shmalloced; i++)
bcopy(&shmsegs[i], &newsegs[i], sizeof(newsegs[0]));
for (; i < shminfo.shmmni; i++) {
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