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vs_alloc can underflow in L2ARC vdevs 

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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
module/zfs/arc.c
View File

@ -3786,7 +3786,8 @@ arc_hdr_l2hdr_destroy(arc_buf_hdr_t *hdr)
{
l2arc_buf_hdr_t *l2hdr = &hdr->b_l2hdr;
l2arc_dev_t *dev = l2hdr->b_dev;
uint64_t psize = arc_hdr_size(hdr);
uint64_t psize = HDR_GET_PSIZE(hdr);
uint64_t asize = vdev_psize_to_asize(dev->l2ad_vdev, psize);
ASSERT(MUTEX_HELD(&dev->l2ad_mtx));
ASSERT(HDR_HAS_L2HDR(hdr));
@ -3796,9 +3797,10 @@ arc_hdr_l2hdr_destroy(arc_buf_hdr_t *hdr)
ARCSTAT_INCR(arcstat_l2_psize, -psize);
ARCSTAT_INCR(arcstat_l2_lsize, -HDR_GET_LSIZE(hdr));
vdev_space_update(dev->l2ad_vdev, -psize, 0, 0);
vdev_space_update(dev->l2ad_vdev, -asize, 0, 0);
(void) zfs_refcount_remove_many(&dev->l2ad_alloc, psize, hdr);
(void) zfs_refcount_remove_many(&dev->l2ad_alloc, arc_hdr_size(hdr),
hdr);
arc_hdr_clear_flags(hdr, ARC_FLAG_HAS_L2HDR);
}
@ -8296,10 +8298,12 @@ top:
list_remove(buflist, hdr);
arc_hdr_clear_flags(hdr, ARC_FLAG_HAS_L2HDR);
ARCSTAT_INCR(arcstat_l2_psize, -arc_hdr_size(hdr));
uint64_t psize = HDR_GET_PSIZE(hdr);
ARCSTAT_INCR(arcstat_l2_psize, -psize);
ARCSTAT_INCR(arcstat_l2_lsize, -HDR_GET_LSIZE(hdr));
bytes_dropped += arc_hdr_size(hdr);
bytes_dropped +=
vdev_psize_to_asize(dev->l2ad_vdev, psize);
(void) zfs_refcount_remove_many(&dev->l2ad_alloc,
arc_hdr_size(hdr), hdr);
}
@ -9015,6 +9019,7 @@ l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t target_sz)
write_psize += psize;
write_asize += asize;
dev->l2ad_hand += asize;
vdev_space_update(dev->l2ad_vdev, asize, 0, 0);
mutex_exit(hash_lock);
@ -9040,7 +9045,6 @@ l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t target_sz)
ARCSTAT_INCR(arcstat_l2_write_bytes, write_psize);
ARCSTAT_INCR(arcstat_l2_lsize, write_lsize);
ARCSTAT_INCR(arcstat_l2_psize, write_psize);
vdev_space_update(dev->l2ad_vdev, write_psize, 0, 0);
/*
* Bump device hand to the device start if it is approaching the end.

6
module/zfs/vdev.c
View File

@ -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;