Date: Wed, 18 Feb 2015 18:12:07 +0000 (UTC) From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r278963 - head/sys/kern Message-ID: <201502181812.t1IIC7Do021265@svn.freebsd.org>
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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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