On Fri, Dec 28, 2012 at 10:19:31AM +0100, Andreas Longwitz wrote: > Konstantin Belousov wrote: > >>> On Thu, Dec 27, 2012 at 12:28:54PM +0100, Andreas Longwitz wrote: > >> db> alltrace (pid 18 and 7126) > >> > >> Tracing command g_journal switcher pid 18 tid 100076 td 0xffffff0002bd5000 > >> sched_switch() at sched_switch+0xde > >> mi_switch() at mi_switch+0x186 > >> sleepq_wait() at sleepq_wait+0x42 > >> __lockmgr_args() at __lockmgr_args+0x49b > >> ffs_copyonwrite() at ffs_copyonwrite+0x19a > >> ffs_geom_strategy() at ffs_geom_strategy+0x1b5 > >> bufwrite() at bufwrite+0xe9 > >> ffs_sbupdate() at ffs_sbupdate+0x12a > >> g_journal_ufs_clean() at g_journal_ufs_clean+0x3e > >> g_journal_switcher() at g_journal_switcher+0xe5e > >> fork_exit() at fork_exit+0x11f > >> fork_trampoline() at fork_trampoline+0xe > >> --- trap 0, rip = 0, rsp = 0xffffff8242ca8cf0, rbp = 0 --- > >> > >> Tracing command mksnap_ffs pid 7126 tid 100157 td 0xffffff000807a470 > >> sched_switch() at sched_switch+0xde > >> mi_switch() at mi_switch+0x186 > >> sleepq_wait() at sleepq_wait+0x42 > >> _sleep() at _sleep+0x373 > >> vn_start_write() at vn_start_write+0xdf > >> ffs_snapshot() at ffs_snapshot+0xe2b > > Can you look up the line number for the ffs_snapshot+0xe2b ? > > (kgdb) list *ffs_snapshot+0xe2b > 0xffffffff8056287b is in ffs_snapshot > (/usr/src/sys/ufs/ffs/ffs_snapshot.c:676). > 671 /* > 672 * Resume operation on filesystem. > 673 */ > 674 vfs_write_resume(vp->v_mount); > 675 vn_start_write(NULL, &wrtmp, V_WAIT); > 676 if (collectsnapstats && starttime.tv_sec > 0) { > 677 nanotime(&endtime); > 678 timespecsub(&endtime, &starttime); > 679 printf("%s: suspended %ld.%03ld sec, redo %ld of %d\n", > 680 vp->v_mount->mnt_stat.f_mntonname, (long)endtime.tv_sec, > > > I think the bug is that vn_start_write() is called while the snaplock > > is owned, after the out1 label in ffs_snapshot() (I am looking at the > > HEAD code). > > You are right, the vn_start_write() is just after the out1 label.
Please try the following patch. It is against HEAD, might need some adjustments for 8. I do the resume and write accounting atomically, not allowing other suspension to intervent between. diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c index 3f65b05..cf49ecb 100644 --- a/sys/kern/vfs_vnops.c +++ b/sys/kern/vfs_vnops.c @@ -1434,6 +1434,40 @@ vn_closefile(fp, td) * proceed. If a suspend request is in progress, we wait until the * suspension is over, and then proceed. */ +static int +vn_start_write_locked(struct mount *mp, int flags) +{ + int error; + + mtx_assert(MNT_MTX(mp), MA_OWNED); + error = 0; + + /* + * Check on status of suspension. + */ + if ((curthread->td_pflags & TDP_IGNSUSP) == 0 || + mp->mnt_susp_owner != curthread) { + while ((mp->mnt_kern_flag & MNTK_SUSPEND) != 0) { + if (flags & V_NOWAIT) { + error = EWOULDBLOCK; + goto unlock; + } + error = msleep(&mp->mnt_flag, MNT_MTX(mp), + (PUSER - 1) | (flags & PCATCH), "suspfs", 0); + if (error) + goto unlock; + } + } + if (flags & V_XSLEEP) + goto unlock; + mp->mnt_writeopcount++; +unlock: + if (error != 0 || (flags & V_XSLEEP) != 0) + MNT_REL(mp); + MNT_IUNLOCK(mp); + return (error); +} + int vn_start_write(vp, mpp, flags) struct vnode *vp; @@ -1470,30 +1504,7 @@ vn_start_write(vp, mpp, flags) if (vp == NULL) MNT_REF(mp); - /* - * Check on status of suspension. - */ - if ((curthread->td_pflags & TDP_IGNSUSP) == 0 || - mp->mnt_susp_owner != curthread) { - while ((mp->mnt_kern_flag & MNTK_SUSPEND) != 0) { - if (flags & V_NOWAIT) { - error = EWOULDBLOCK; - goto unlock; - } - error = msleep(&mp->mnt_flag, MNT_MTX(mp), - (PUSER - 1) | (flags & PCATCH), "suspfs", 0); - if (error) - goto unlock; - } - } - if (flags & V_XSLEEP) - goto unlock; - mp->mnt_writeopcount++; -unlock: - if (error != 0 || (flags & V_XSLEEP) != 0) - MNT_REL(mp); - MNT_IUNLOCK(mp); - return (error); + return (vn_start_write_locked(mp, flags)); } /* @@ -1639,8 +1650,7 @@ vfs_write_suspend(mp) * Request a filesystem to resume write operations. */ void -vfs_write_resume(mp) - struct mount *mp; +vfs_write_resume_flags(struct mount *mp, int flags) { MNT_ILOCK(mp); @@ -1652,10 +1662,25 @@ vfs_write_resume(mp) wakeup(&mp->mnt_writeopcount); wakeup(&mp->mnt_flag); curthread->td_pflags &= ~TDP_IGNSUSP; + if ((flags & VR_START_WRITE) != 0) { + MNT_REF(mp); + mp->mnt_writeopcount++; + } MNT_IUNLOCK(mp); VFS_SUSP_CLEAN(mp); - } else + } else if ((flags & VR_START_WRITE) != 0) { + MNT_REF(mp); + vn_start_write_locked(mp, 0); + } else { MNT_IUNLOCK(mp); + } +} + +void +vfs_write_resume(struct mount *mp) +{ + + vfs_write_resume_flags(mp, 0); } /* diff --git a/sys/sys/vnode.h b/sys/sys/vnode.h index 42f9e5f..4371b40 100644 --- a/sys/sys/vnode.h +++ b/sys/sys/vnode.h @@ -392,6 +392,8 @@ extern int vttoif_tab[]; #define V_NOWAIT 0x0002 /* vn_start_write: don't sleep for suspend */ #define V_XSLEEP 0x0004 /* vn_start_write: just return after sleep */ +#define VR_START_WRITE 0x0001 /* vfs_write_resume: start write atomically */ + #define VREF(vp) vref(vp) #ifdef DIAGNOSTIC @@ -701,6 +703,7 @@ int vn_io_fault_uiomove(char *data, int xfersize, struct uio *uio); int vfs_cache_lookup(struct vop_lookup_args *ap); void vfs_timestamp(struct timespec *); void vfs_write_resume(struct mount *mp); +void vfs_write_resume_flags(struct mount *mp, int flags); int vfs_write_suspend(struct mount *mp); int vop_stdbmap(struct vop_bmap_args *); int vop_stdfsync(struct vop_fsync_args *); diff --git a/sys/ufs/ffs/ffs_snapshot.c b/sys/ufs/ffs/ffs_snapshot.c index e528509..25ad79c 100644 --- a/sys/ufs/ffs/ffs_snapshot.c +++ b/sys/ufs/ffs/ffs_snapshot.c @@ -687,8 +687,7 @@ out1: /* * Resume operation on filesystem. */ - vfs_write_resume(vp->v_mount); - vn_start_write(NULL, &wrtmp, V_WAIT); + vfs_write_resume_flags(vp->v_mount, VR_START_WRITE); if (collectsnapstats && starttime.tv_sec > 0) { nanotime(&endtime); timespecsub(&endtime, &starttime);
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