Date: Tue, 10 May 2016 16:49:50 +0000 (UTC) From: Alan Somers <asomers@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-10@freebsd.org Subject: svn commit: r299376 - stable/10/sys/cddl/contrib/opensolaris/uts/common/fs/zfs Message-ID: <201605101649.u4AGnoHv091943@repo.freebsd.org>
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Author: asomers Date: Tue May 10 16:49:50 2016 New Revision: 299376 URL: https://svnweb.freebsd.org/changeset/base/299376 Log: MFC 297868 Fix rare double free in vdev_geom_attrchanged sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c Don't drop the g_topology_lock before freeing old_physpath. That opens up a race where one thread can call vdev_geom_attrchanged, set old_physpath, drop the g_topology_lock, then block trying to acquire the SCL_STATE lock. Then another thread can come into vdev_geom_attrchanged, set old_physpath to the same value, and proceed to free it. When the first thread resumes, it will free the same location. It turns out that the SCL_STATE lock isn't needed. It was originally added by gibbs to protect vd->vdev_physpath while updating the same. However, the update process subsequently was switched to an atomic operation (a pointer swap). Now, there is no need for the SCL_STATE lock, and hence no need to drop the g_topology_lock. Modified: stable/10/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c Directory Properties: stable/10/ (props changed) Modified: stable/10/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c ============================================================================== --- stable/10/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c Tue May 10 16:40:19 2016 (r299375) +++ stable/10/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c Tue May 10 16:49:50 2016 (r299376) @@ -110,27 +110,14 @@ vdev_geom_attrchanged(struct g_consumer if (error == 0) { char *old_physpath; + /* g_topology lock ensures that vdev has not been closed */ + g_topology_assert(); old_physpath = vd->vdev_physpath; vd->vdev_physpath = spa_strdup(physpath); spa_async_request(spa, SPA_ASYNC_CONFIG_UPDATE); - if (old_physpath != NULL) { - int held_lock; - - held_lock = spa_config_held(spa, SCL_STATE, RW_WRITER); - if (held_lock == 0) { - g_topology_unlock(); - spa_config_enter(spa, SCL_STATE, FTAG, - RW_WRITER); - } - + if (old_physpath != NULL) spa_strfree(old_physpath); - - if (held_lock == 0) { - spa_config_exit(spa, SCL_STATE, FTAG); - g_topology_lock(); - } - } } g_free(physpath); }
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