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
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@ -3786,7 +3786,8 @@ arc_hdr_l2hdr_destroy(arc_buf_hdr_t *hdr)
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{
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l2arc_buf_hdr_t *l2hdr = &hdr->b_l2hdr;
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l2arc_dev_t *dev = l2hdr->b_dev;
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uint64_t psize = arc_hdr_size(hdr);
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uint64_t psize = HDR_GET_PSIZE(hdr);
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uint64_t asize = vdev_psize_to_asize(dev->l2ad_vdev, psize);
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ASSERT(MUTEX_HELD(&dev->l2ad_mtx));
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ASSERT(HDR_HAS_L2HDR(hdr));
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@ -3796,9 +3797,10 @@ arc_hdr_l2hdr_destroy(arc_buf_hdr_t *hdr)
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ARCSTAT_INCR(arcstat_l2_psize, -psize);
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ARCSTAT_INCR(arcstat_l2_lsize, -HDR_GET_LSIZE(hdr));
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vdev_space_update(dev->l2ad_vdev, -psize, 0, 0);
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vdev_space_update(dev->l2ad_vdev, -asize, 0, 0);
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(void) zfs_refcount_remove_many(&dev->l2ad_alloc, psize, hdr);
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(void) zfs_refcount_remove_many(&dev->l2ad_alloc, arc_hdr_size(hdr),
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hdr);
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arc_hdr_clear_flags(hdr, ARC_FLAG_HAS_L2HDR);
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}
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@ -8296,10 +8298,12 @@ l2arc_write_done(zio_t *zio)
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list_remove(buflist, hdr);
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arc_hdr_clear_flags(hdr, ARC_FLAG_HAS_L2HDR);
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ARCSTAT_INCR(arcstat_l2_psize, -arc_hdr_size(hdr));
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uint64_t psize = HDR_GET_PSIZE(hdr);
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ARCSTAT_INCR(arcstat_l2_psize, -psize);
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ARCSTAT_INCR(arcstat_l2_lsize, -HDR_GET_LSIZE(hdr));
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bytes_dropped += arc_hdr_size(hdr);
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bytes_dropped +=
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vdev_psize_to_asize(dev->l2ad_vdev, psize);
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(void) zfs_refcount_remove_many(&dev->l2ad_alloc,
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arc_hdr_size(hdr), hdr);
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}
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@ -9015,6 +9019,7 @@ l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t target_sz)
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write_psize += psize;
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write_asize += asize;
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dev->l2ad_hand += asize;
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vdev_space_update(dev->l2ad_vdev, asize, 0, 0);
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mutex_exit(hash_lock);
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@ -9040,7 +9045,6 @@ l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t target_sz)
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ARCSTAT_INCR(arcstat_l2_write_bytes, write_psize);
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ARCSTAT_INCR(arcstat_l2_lsize, write_lsize);
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ARCSTAT_INCR(arcstat_l2_psize, write_psize);
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vdev_space_update(dev->l2ad_vdev, write_psize, 0, 0);
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/*
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* Bump device hand to the device start if it is approaching the end.
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@ -4162,6 +4162,11 @@ vdev_space_update(vdev_t *vd, int64_t alloc_delta, int64_t defer_delta,
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dspace_delta = vdev_deflated_space(vd, space_delta);
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mutex_enter(&vd->vdev_stat_lock);
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/* ensure we won't underflow */
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if (alloc_delta < 0) {
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ASSERT3U(vd->vdev_stat.vs_alloc, >=, -alloc_delta);
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}
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vd->vdev_stat.vs_alloc += alloc_delta;
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vd->vdev_stat.vs_space += space_delta;
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vd->vdev_stat.vs_dspace += dspace_delta;
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@ -4169,6 +4174,7 @@ vdev_space_update(vdev_t *vd, int64_t alloc_delta, int64_t defer_delta,
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/* every class but log contributes to root space stats */
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if (vd->vdev_mg != NULL && !vd->vdev_islog) {
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ASSERT(!vd->vdev_isl2cache);
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mutex_enter(&rvd->vdev_stat_lock);
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rvd->vdev_stat.vs_alloc += alloc_delta;
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rvd->vdev_stat.vs_space += space_delta;
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