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vs_alloc can underflow in L2ARC vdevs

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The current L2 ARC device code consistently uses psize to
increment vs_alloc but varies between psize and lsize when
decrementing it. The result of this behavior is that
vs_alloc can be decremented more that it is incremented
and underflow. This patch changes the code so asize is
used anywhere.

In addition, it ensures that vs_alloc gets incremented by
the L2 ARC device code as buffers are written and not at
the end of the l2arc_write_buffers() routine. The latter
(and old) way would temporarily underflow vs_alloc as
buffers that were just written, would be destroyed while
l2arc_write_buffers() was still looping.

Reviewed-by: Matt Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Serapheim Dimitropoulos <serapheim@delphix.com>
Closes #8298
This commit is contained in:
Serapheim Dimitropoulos
2019-01-31 09:16:39 -08:00
committed by Brian Behlendorf
parent 2747f599ff
commit 7558997d2f
2 changed files with 16 additions and 6 deletions
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module/zfs/vdev.c
+6
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@@ -4162,6 +4162,11 @@ vdev_space_update(vdev_t *vd, int64_t alloc_delta, int64_t defer_delta,
dspace_delta = vdev_deflated_space(vd, space_delta);
mutex_enter(&vd->vdev_stat_lock);
/* ensure we won't underflow */
if (alloc_delta < 0) {
ASSERT3U(vd->vdev_stat.vs_alloc, >=, -alloc_delta);
}
vd->vdev_stat.vs_alloc += alloc_delta;
vd->vdev_stat.vs_space += space_delta;
vd->vdev_stat.vs_dspace += dspace_delta;
@@ -4169,6 +4174,7 @@ vdev_space_update(vdev_t *vd, int64_t alloc_delta, int64_t defer_delta,
/* every class but log contributes to root space stats */
if (vd->vdev_mg != NULL && !vd->vdev_islog) {
ASSERT(!vd->vdev_isl2cache);
mutex_enter(&rvd->vdev_stat_lock);
rvd->vdev_stat.vs_alloc += alloc_delta;
rvd->vdev_stat.vs_space += space_delta;