svn commit: r274628 - head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs
Steven Hartland
steven at multiplay.co.uk
Mon Nov 17 15:12:55 UTC 2014
Looks like this could have introduced random data corruption, have you
seen this in practice?
On 17/11/2014 14:45, Andriy Gapon wrote:
> Author: avg
> Date: Mon Nov 17 14:45:42 2014
> New Revision: 274628
> URL: https://svnweb.freebsd.org/changeset/base/274628
>
> Log:
> l2arc: restore correct rounding up of asize of compressed data
>
> This rounding up was lost in a mismerge of illumos code.
> See r268075 MFV r267565.
> After that commit zio_compress_data() no longer performs any compressed
> size adjustment, so it needs to be done externally. On FreeBSD we round
> up the size using vdev_ashift rather than SPA_MINBLOCKSIZE so that 4KB
> devices are properly supported.
>
> Additionally, zero out the buffer tail only if compression succeeds.
> The compression is considered successful if the size of compressed
> data after rounding up to account for the vdev ashift is less than the
> original data size. It does not make sense to have the data compressed
> if all the savings are lost to rounding up.
> With the new zio_compress_data() it could have been possible that the
> rounded compressed size would be greater than the original size and thus
> we could zero beyond the allocated buffer if the zeroing code was kept
> at the original place.
>
> Discussed with: delphij, gibbs
> MFC after: 2 weeks
> X-MFC with: r274627
>
> Modified:
> head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
>
> Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
> ==============================================================================
> --- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c Mon Nov 17 14:16:02 2014 (r274627)
> +++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c Mon Nov 17 14:45:42 2014 (r274628)
> @@ -5326,12 +5326,6 @@ l2arc_compress_buf(l2arc_buf_hdr_t *l2hd
> csize = zio_compress_data(ZIO_COMPRESS_LZ4, l2hdr->b_tmp_cdata,
> cdata, l2hdr->b_asize);
>
> - rounded = P2ROUNDUP(csize, (size_t)SPA_MINBLOCKSIZE);
> - if (rounded > csize) {
> - bzero((char *)cdata + csize, rounded - csize);
> - csize = rounded;
> - }
> -
> if (csize == 0) {
> /* zero block, indicate that there's nothing to write */
> zio_data_buf_free(cdata, len);
> @@ -5340,11 +5334,19 @@ l2arc_compress_buf(l2arc_buf_hdr_t *l2hd
> l2hdr->b_tmp_cdata = NULL;
> ARCSTAT_BUMP(arcstat_l2_compress_zeros);
> return (B_TRUE);
> - } else if (csize > 0 && csize < len) {
> + }
> +
> + rounded = P2ROUNDUP(csize,
> + (size_t)1 << l2hdr->b_dev->l2ad_vdev->vdev_ashift);
> + if (rounded < len) {
> /*
> * Compression succeeded, we'll keep the cdata around for
> * writing and release it afterwards.
> */
> + if (rounded > csize) {
> + bzero((char *)cdata + csize, rounded - csize);
> + csize = rounded;
> + }
> l2hdr->b_compress = ZIO_COMPRESS_LZ4;
> l2hdr->b_asize = csize;
> l2hdr->b_tmp_cdata = cdata;
>
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