On Fri, Aug 18, 2017 at 10:06:07AM -0700, Darrick J. Wong wrote:
> On Fri, Aug 18, 2017 at 12:05:16AM -0700, Christoph Hellwig wrote:
> > On Thu, Aug 17, 2017 at 04:31:29PM -0700, Darrick J. Wong wrote:
> > > Hi all,
> > >
> > > This RFC combines all the random little fixes and improvements to the
> > > verifiers that we've been talking about for the past month or so into a
> > > single patch series!
> > >
> > > We start by refactoring the long format btree block header verifier into
> > > a single helper functionn and de-macroing dir block verifiers to make
> > > them less shouty. Next, we change verifier functions to return the
> > > approximate instruction pointer of the faulting test so that we can
> > > report more precise fault information to dmesg/tracepoints.
> >
> > Just jumping here quickly because I don't have time for a detailed
> > review:
> >
> > How good does this instruction pointer thing resolved to the actual
> > issue?
>
> Ugh, it's terrible once you turn on the optimizer.
>
> if (!xfs_sb_version_hascrc(&mp->m_sb))
> return __this_address;
> if (!uuid_equal(&block->bb_u.s.bb_uuid, &mp->m_sb.sb_meta_uuid))
> return __this_address;
> if (block->bb_u.s.bb_blkno != cpu_to_be64(bp->b_bn))
> return __this_address;
> if (pag && be32_to_cpu(block->bb_u.s.bb_owner) != pag->pag_agno)
> return __this_address;
> return NULL;
>
> becomes:
>
> if (!xfs_sb_version_hascrc(&mp->m_sb))
> goto out;
> if (!uuid_equal(&block->bb_u.s.bb_uuid, &mp->m_sb.sb_meta_uuid))
> goto out;
> if (block->bb_u.s.bb_blkno != cpu_to_be64(bp->b_bn))
> goto out;
> if (pag && be32_to_cpu(block->bb_u.s.bb_owner) != pag->pag_agno)
> goto out;
> return NULL;
> out:
> return __this_address;
>
> ...which is totally worthless, unless we want to compile all the verifier
> functions with __attribute__((optimize("O0"))), which is bogus.
>
> <sigh> Back to the drawing board on that one.
Ok, there's /slightly/ less awful way to prevent gcc from optimizing the
verifier function to the point of imprecise pointer value, but it involves
writing to a volatile int:
/* stupidly prevent gcc from over-optimizing getting the instruction ptr */
extern volatile int xfs_lineno;
#define __this_address ({ __label__ __here; __here: xfs_lineno = __LINE__; &&__here; })
<grumble> Yucky, but it more or less works.
--D
>
> > I'm currently watching a customer issue where a write verifier
> > triggers, and I gave them a patch to add a debug print to every failing
> > statement, including printing out the mismatch values if it's not
> > simply a binary comparism. I though about preparing that patch as
> > well as others for mainline. Here is the one I have at the moment:
> >
> > ---
> > From 6c5e2efc6f857228461d439feb3c98be58fb9744 Mon Sep 17 00:00:00 2001
> > From: Christoph Hellwig <hch@xxxxxx>
> > Date: Sat, 5 Aug 2017 16:34:15 +0200
> > Subject: xfs: print verbose information on dir leaf verifier failures
> >
> > Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> > ---
> > fs/xfs/libxfs/xfs_dir2_leaf.c | 33 ++++++++++++++++++++++++++-------
> > 1 file changed, 26 insertions(+), 7 deletions(-)
> >
> > diff --git a/fs/xfs/libxfs/xfs_dir2_leaf.c b/fs/xfs/libxfs/xfs_dir2_leaf.c
> > index b887fb2a2bcf..4386c68f72c6 100644
> > --- a/fs/xfs/libxfs/xfs_dir2_leaf.c
> > +++ b/fs/xfs/libxfs/xfs_dir2_leaf.c
> > @@ -113,27 +113,37 @@ xfs_dir3_leaf_check_int(
> > * Should factor in the size of the bests table as well.
> > * We can deduce a value for that from di_size.
> > */
> > - if (hdr->count > ops->leaf_max_ents(geo))
> > + if (hdr->count > ops->leaf_max_ents(geo)) {
> > + xfs_warn(mp, "count (%d) above max (%d)\n",
> > + hdr->count, ops->leaf_max_ents(geo));
> > return false;
> > + }
> >
> > /* Leaves and bests don't overlap in leaf format. */
> > if ((hdr->magic == XFS_DIR2_LEAF1_MAGIC ||
> > hdr->magic == XFS_DIR3_LEAF1_MAGIC) &&
> > - (char *)&ents[hdr->count] > (char *)xfs_dir2_leaf_bests_p(ltp))
> > + (char *)&ents[hdr->count] > (char *)xfs_dir2_leaf_bests_p(ltp)) {
> > + xfs_warn(mp, "ents overlappings bests\n");
> > return false;
> > + }
> >
> > /* Check hash value order, count stale entries. */
> > for (i = stale = 0; i < hdr->count; i++) {
> > if (i + 1 < hdr->count) {
> > if (be32_to_cpu(ents[i].hashval) >
> > - be32_to_cpu(ents[i + 1].hashval))
> > + be32_to_cpu(ents[i + 1].hashval)) {
> > + xfs_warn(mp, "broken hash order\n");
> > return false;
> > + }
> > }
> > if (ents[i].address == cpu_to_be32(XFS_DIR2_NULL_DATAPTR))
> > stale++;
> > }
> > - if (hdr->stale != stale)
> > + if (hdr->stale != stale) {
> > + xfs_warn(mp, "incorrect stalte count (%d, expected %d)\n",
> > + hdr->stale, stale);
> > return false;
> > + }
> > return true;
> > }
> >
> > @@ -159,12 +169,21 @@ xfs_dir3_leaf_verify(
> > magic3 = (magic == XFS_DIR2_LEAF1_MAGIC) ? XFS_DIR3_LEAF1_MAGIC
> > : XFS_DIR3_LEAFN_MAGIC;
> >
> > - if (leaf3->info.hdr.magic != cpu_to_be16(magic3))
> > + if (leaf3->info.hdr.magic != cpu_to_be16(magic3)) {
> > + xfs_warn(mp, "incorrect magic number (0x%hx, expected 0x%hx)\n",
> > + leaf3->info.hdr.magic, magic3);
> > return false;
> > - if (!uuid_equal(&leaf3->info.uuid, &mp->m_sb.sb_meta_uuid))
> > + }
> > + if (!uuid_equal(&leaf3->info.uuid, &mp->m_sb.sb_meta_uuid)) {
> > + xfs_warn(mp, "incorrect uuid, (%pUb, expected %pUb)\n",
> > + &leaf3->info.uuid, &mp->m_sb.sb_meta_uuid);
> > return false;
> > - if (be64_to_cpu(leaf3->info.blkno) != bp->b_bn)
> > + }
> > + if (be64_to_cpu(leaf3->info.blkno) != bp->b_bn) {
> > + xfs_warn(mp, "incorrect blkno, (%lld, expected %lld)\n",
> > + be64_to_cpu(leaf3->info.blkno), bp->b_bn);
> > return false;
> > + }
> > if (!xfs_log_check_lsn(mp, be64_to_cpu(leaf3->info.lsn)))
> > return false;
> > } else {
> > --
> > 2.11.0
> >
> > --
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