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ufs: handle LoR between snap lock and vnode lock

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(cherry picked from commit ddf162d1d1)

Differential Revision: https://reviews.freebsd.org/D33946
This commit is contained in:
Kirk McKusick 2022-01-27 23:00:51 -08:00
parent 47c0781405
commit 3364fdf16a
1 changed files with 54 additions and 34 deletions
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88
sys/ufs/ffs/ffs_snapshot.c
View file

@ -175,6 +175,7 @@ static int mapacct_ufs2(struct vnode *, ufs2_daddr_t *, ufs2_daddr_t *,
struct fs *, ufs_lbn_t, int);
static int readblock(struct vnode *vp, struct buf *, ufs2_daddr_t);
static void try_free_snapdata(struct vnode *devvp);
static void revert_snaplock(struct vnode *, struct vnode *, struct snapdata *);
static struct snapdata *ffs_snapdata_acquire(struct vnode *devvp);
static int ffs_bp_snapblk(struct vnode *, struct buf *);
@ -1649,7 +1650,7 @@ ffs_snapremove(vp)
struct buf *ibp;
struct fs *fs;
ufs2_daddr_t numblks, blkno, dblk;
int error, i, last, loc;
int error, last, loc;
struct snapdata *sn;
ip = VTOI(vp);
@ -1667,20 +1668,10 @@ ffs_snapremove(vp)
sn = devvp->v_rdev->si_snapdata;
TAILQ_REMOVE(&sn->sn_head, ip, i_nextsnap);
ip->i_nextsnap.tqe_prev = 0;
VI_UNLOCK(devvp);
lockmgr(&vp->v_lock, LK_EXCLUSIVE, NULL);
for (i = 0; i < sn->sn_lock.lk_recurse; i++)
lockmgr(&vp->v_lock, LK_EXCLUSIVE, NULL);
KASSERT(vp->v_vnlock == &sn->sn_lock,
("ffs_snapremove: lost lock mutation"));
vp->v_vnlock = &vp->v_lock;
VI_LOCK(devvp);
while (sn->sn_lock.lk_recurse > 0)
lockmgr(&sn->sn_lock, LK_RELEASE, NULL);
lockmgr(&sn->sn_lock, LK_RELEASE, NULL);
revert_snaplock(vp, devvp, sn);
try_free_snapdata(devvp);
} else
VI_UNLOCK(devvp);
}
VI_UNLOCK(devvp);
/*
* Clear all BLK_NOCOPY fields. Pass any block claims to other
* snapshots that want them (see ffs_snapblkfree below).
@ -2156,27 +2147,18 @@ ffs_snapshot_unmount(mp)
xp->i_nextsnap.tqe_prev = 0;
lockmgr(&sn->sn_lock, LK_INTERLOCK | LK_EXCLUSIVE,
VI_MTX(devvp));
/*
* Avoid LOR with above snapshot lock. The LK_NOWAIT should
* never fail as the lock is currently unused. Rather than
* panic, we recover by doing the blocking lock.
*/
if (lockmgr(&vp->v_lock, LK_EXCLUSIVE | LK_NOWAIT, NULL) != 0) {
printf("ffs_snapshot_unmount: Unexpected LK_NOWAIT "
"failure\n");
lockmgr(&vp->v_lock, LK_EXCLUSIVE, NULL);
}
KASSERT(vp->v_vnlock == &sn->sn_lock,
("ffs_snapshot_unmount: lost lock mutation"));
vp->v_vnlock = &vp->v_lock;
lockmgr(&vp->v_lock, LK_RELEASE, NULL);
lockmgr(&sn->sn_lock, LK_RELEASE, NULL);
if (xp->i_effnlink > 0)
vrele(vp);
VI_LOCK(devvp);
revert_snaplock(vp, devvp, sn);
lockmgr(&vp->v_lock, LK_RELEASE, NULL);
if (xp->i_effnlink > 0) {
VI_UNLOCK(devvp);
vrele(vp);
VI_LOCK(devvp);
}
sn = devvp->v_rdev->si_snapdata;
}
try_free_snapdata(devvp);
VI_UNLOCK(devvp);
}
/*
@ -2680,10 +2662,8 @@ try_free_snapdata(struct vnode *devvp)
sn = devvp->v_rdev->si_snapdata;
if (sn == NULL || TAILQ_FIRST(&sn->sn_head) != NULL ||
(devvp->v_vflag & VV_COPYONWRITE) == 0) {
VI_UNLOCK(devvp);
(devvp->v_vflag & VV_COPYONWRITE) == 0)
return;
}
devvp->v_rdev->si_snapdata = NULL;
devvp->v_vflag &= ~VV_COPYONWRITE;
@ -2695,6 +2675,46 @@ try_free_snapdata(struct vnode *devvp)
if (snapblklist != NULL)
free(snapblklist, M_UFSMNT);
ffs_snapdata_free(sn);
VI_LOCK(devvp);
}
/*
* Revert a vnode lock from using the snapshot lock back to its own lock.
*
* Aquire a lock on the vnode's own lock and release the lock on the
* snapshot lock. If there are any recursions on the snapshot lock
* get the same number of recursions on the vnode's own lock.
*/
static void
revert_snaplock(vp, devvp, sn)
struct vnode *vp;
struct vnode *devvp;
struct snapdata *sn;
{
int i;
ASSERT_VI_LOCKED(devvp, "revert_snaplock");
/*
* Avoid LOR with snapshot lock. The LK_NOWAIT should
* never fail as the lock is currently unused. Rather than
* panic, we recover by doing the blocking lock.
*/
for (i = 0; i <= sn->sn_lock.lk_recurse; i++) {
if (lockmgr(&vp->v_lock, LK_EXCLUSIVE | LK_NOWAIT |
LK_INTERLOCK, VI_MTX(devvp)) != 0) {
printf("revert_snaplock: Unexpected LK_NOWAIT "
"failure\n");
lockmgr(&vp->v_lock, LK_EXCLUSIVE | LK_INTERLOCK,
VI_MTX(devvp));
}
VI_LOCK(devvp);
}
KASSERT(vp->v_vnlock == &sn->sn_lock,
("revert_snaplock: lost lock mutation"));
vp->v_vnlock = &vp->v_lock;
while (sn->sn_lock.lk_recurse > 0)
lockmgr(&sn->sn_lock, LK_RELEASE, NULL);
lockmgr(&sn->sn_lock, LK_RELEASE, NULL);
}
static struct snapdata *