Author: kib
Date: Tue Jul 9 20:49:32 2013
New Revision: 253106
URL: http://svnweb.freebsd.org/changeset/base/253106
Log:
There are several code sequences like
vfs_busy(mp);
vfs_write_suspend(mp);
which are problematic if other thread starts unmount between two
calls. The unmount starts a write, while vfs_write_suspend() drain
writers. On the other hand, unmount drains busy references, causing
the deadlock.
Add a flag argument to vfs_write_suspend and require the callers of it
to specify VS_SKIP_UNMOUNT flag, when the call is performed not in the
mount path, i.e. the covered vnode is not locked. The suspension is
not attempted if VS_SKIP_UNMOUNT is specified and unmount is in
progress.
Reported and tested by: Andreas Longwitz <longw...@incore.de>
Sponsored by: The FreeBSD Foundation
MFC after: 3 weeks
Modified:
head/sys/geom/journal/g_journal.c
head/sys/kern/vfs_vnops.c
head/sys/sys/vnode.h
head/sys/ufs/ffs/ffs_snapshot.c
head/sys/ufs/ffs/ffs_suspend.c
head/sys/ufs/ffs/ffs_vfsops.c
Modified: head/sys/geom/journal/g_journal.c
==============================================================================
--- head/sys/geom/journal/g_journal.c Tue Jul 9 19:12:47 2013
(r253105)
+++ head/sys/geom/journal/g_journal.c Tue Jul 9 20:49:32 2013
(r253106)
@@ -2960,7 +2960,7 @@ g_journal_do_switch(struct g_class *clas
GJ_TIMER_STOP(1, &bt, "BIO_FLUSH time of %s", sc->sc_name);
GJ_TIMER_START(1, &bt);
- error = vfs_write_suspend(mp);
+ error = vfs_write_suspend(mp, VS_SKIP_UNMOUNT);
GJ_TIMER_STOP(1, &bt, "Suspend time of %s", mountpoint);
if (error != 0) {
GJ_DEBUG(0, "Cannot suspend file system %s (error=%d).",
Modified: head/sys/kern/vfs_vnops.c
==============================================================================
--- head/sys/kern/vfs_vnops.c Tue Jul 9 19:12:47 2013 (r253105)
+++ head/sys/kern/vfs_vnops.c Tue Jul 9 20:49:32 2013 (r253106)
@@ -1668,8 +1668,7 @@ vn_finished_secondary_write(mp)
* Request a filesystem to suspend write operations.
*/
int
-vfs_write_suspend(mp)
- struct mount *mp;
+vfs_write_suspend(struct mount *mp, int flags)
{
int error;
@@ -1680,6 +1679,21 @@ vfs_write_suspend(mp)
}
while (mp->mnt_kern_flag & MNTK_SUSPEND)
msleep(&mp->mnt_flag, MNT_MTX(mp), PUSER - 1, "wsuspfs", 0);
+
+ /*
+ * Unmount holds a write reference on the mount point. If we
+ * own busy reference and drain for writers, we deadlock with
+ * the reference draining in the unmount path. Callers of
+ * vfs_write_suspend() must specify VS_SKIP_UNMOUNT if
+ * vfs_busy() reference is owned and caller is not in the
+ * unmount context.
+ */
+ if ((flags & VS_SKIP_UNMOUNT) != 0 &&
+ (mp->mnt_kern_flag & MNTK_UNMOUNT) != 0) {
+ MNT_IUNLOCK(mp);
+ return (EBUSY);
+ }
+
mp->mnt_kern_flag |= MNTK_SUSPEND;
mp->mnt_susp_owner = curthread;
if (mp->mnt_writeopcount > 0)
Modified: head/sys/sys/vnode.h
==============================================================================
--- head/sys/sys/vnode.h Tue Jul 9 19:12:47 2013 (r253105)
+++ head/sys/sys/vnode.h Tue Jul 9 20:49:32 2013 (r253106)
@@ -398,6 +398,9 @@ extern int vttoif_tab[];
#define VR_START_WRITE 0x0001 /* vfs_write_resume: start write
atomically */
#define VR_NO_SUSPCLR 0x0002 /* vfs_write_resume: do not clear
suspension */
+#define VS_SKIP_UNMOUNT 0x0001 /* vfs_write_suspend: fail if the
+ filesystem is being unmounted */
+
#define VREF(vp) vref(vp)
#ifdef DIAGNOSTIC
@@ -711,7 +714,7 @@ int vn_io_fault_pgmove(vm_page_t ma[], v
int vfs_cache_lookup(struct vop_lookup_args *ap);
void vfs_timestamp(struct timespec *);
void vfs_write_resume(struct mount *mp, int flags);
-int vfs_write_suspend(struct mount *mp);
+int vfs_write_suspend(struct mount *mp, int flags);
int vop_stdbmap(struct vop_bmap_args *);
int vop_stdfsync(struct vop_fsync_args *);
int vop_stdgetwritemount(struct vop_getwritemount_args *);
Modified: head/sys/ufs/ffs/ffs_snapshot.c
==============================================================================
--- head/sys/ufs/ffs/ffs_snapshot.c Tue Jul 9 19:12:47 2013
(r253105)
+++ head/sys/ufs/ffs/ffs_snapshot.c Tue Jul 9 20:49:32 2013
(r253106)
@@ -423,7 +423,7 @@ restart:
*/
for (;;) {
vn_finished_write(wrtmp);
- if ((error = vfs_write_suspend(vp->v_mount)) != 0) {
+ if ((error = vfs_write_suspend(vp->v_mount, 0)) != 0) {
vn_start_write(NULL, &wrtmp, V_WAIT);
vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
goto out;
Modified: head/sys/ufs/ffs/ffs_suspend.c
==============================================================================
--- head/sys/ufs/ffs/ffs_suspend.c Tue Jul 9 19:12:47 2013
(r253105)
+++ head/sys/ufs/ffs/ffs_suspend.c Tue Jul 9 20:49:32 2013
(r253106)
@@ -206,7 +206,7 @@ ffs_susp_suspend(struct mount *mp)
return (EPERM);
#endif
- if ((error = vfs_write_suspend(mp)) != 0)
+ if ((error = vfs_write_suspend(mp, VS_SKIP_UNMOUNT)) != 0)
return (error);
ump->um_writesuspended = 1;
Modified: head/sys/ufs/ffs/ffs_vfsops.c
==============================================================================
--- head/sys/ufs/ffs/ffs_vfsops.c Tue Jul 9 19:12:47 2013
(r253105)
+++ head/sys/ufs/ffs/ffs_vfsops.c Tue Jul 9 20:49:32 2013
(r253106)
@@ -257,7 +257,7 @@ ffs_mount(struct mount *mp)
return (error);
for (;;) {
vn_finished_write(mp);
- if ((error = vfs_write_suspend(mp)) != 0)
+ if ((error = vfs_write_suspend(mp, 0)) != 0)
return (error);
MNT_ILOCK(mp);
if (mp->mnt_kern_flag & MNTK_SUSPENDED) {
@@ -1255,7 +1255,7 @@ ffs_unmount(mp, mntflags)
*/
for (;;) {
vn_finished_write(mp);
- if ((error = vfs_write_suspend(mp)) != 0)
+ if ((error = vfs_write_suspend(mp, 0)) != 0)
return (error);
MNT_ILOCK(mp);
if (mp->mnt_kern_flag & MNTK_SUSPENDED) {
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