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    Subject[PATCH 5.9 426/757] xfs: fix high key handling in the rt allocators query_range function
    Date
    From: Darrick J. Wong <darrick.wong@oracle.com>

    [ Upstream commit d88850bd5516a77c6f727e8b6cefb64e0cc929c7 ]

    Fix some off-by-one errors in xfs_rtalloc_query_range. The highest key
    in the realtime bitmap is always one less than the number of rt extents,
    which means that the key clamp at the start of the function is wrong.
    The 4th argument to xfs_rtfind_forw is the highest rt extent that we
    want to probe, which means that passing 1 less than the high key is
    wrong. Finally, drop the rem variable that controls the loop because we
    can compare the iteration point (rtstart) against the high key directly.

    The sordid history of this function is that the original commit (fb3c3)
    incorrectly passed (high_rec->ar_startblock - 1) as the 'limit' parameter
    to xfs_rtfind_forw. This was wrong because the "high key" is supposed
    to be the largest key for which the caller wants result rows, not the
    key for the first row that could possibly be outside the range that the
    caller wants to see.

    A subsequent attempt (8ad56) to strengthen the parameter checking added
    incorrect clamping of the parameters to the number of rt blocks in the
    system (despite the bitmap functions all taking units of rt extents) to
    avoid querying ranges past the end of rt bitmap file but failed to fix
    the incorrect _rtfind_forw parameter. The original _rtfind_forw
    parameter error then survived the conversion of the startblock and
    blockcount fields to rt extents (a0e5c), and the most recent off-by-one
    fix (a3a37) thought it was patching a problem when the end of the rt
    volume is not in use, but none of these fixes actually solved the
    original problem that the author was confused about the "limit" argument
    to xfs_rtfind_forw.

    Sadly, all four of these patches were written by this author and even
    his own usage of this function and rt testing were inadequate to get
    this fixed quickly.

    Original-problem: fb3c3de2f65c ("xfs: add a couple of queries to iterate free extents in the rtbitmap")
    Not-fixed-by: 8ad560d2565e ("xfs: strengthen rtalloc query range checks")
    Not-fixed-by: a0e5c435babd ("xfs: fix xfs_rtalloc_rec units")
    Fixes: a3a374bf1889 ("xfs: fix off-by-one error in xfs_rtalloc_query_range")
    Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
    Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/xfs/libxfs/xfs_rtbitmap.c | 11 ++++-------
    1 file changed, 4 insertions(+), 7 deletions(-)

    diff --git a/fs/xfs/libxfs/xfs_rtbitmap.c b/fs/xfs/libxfs/xfs_rtbitmap.c
    index 1d9fa8a300f15..6c1aba16113c5 100644
    --- a/fs/xfs/libxfs/xfs_rtbitmap.c
    +++ b/fs/xfs/libxfs/xfs_rtbitmap.c
    @@ -1018,7 +1018,6 @@ xfs_rtalloc_query_range(
    struct xfs_mount *mp = tp->t_mountp;
    xfs_rtblock_t rtstart;
    xfs_rtblock_t rtend;
    - xfs_rtblock_t rem;
    int is_free;
    int error = 0;

    @@ -1027,13 +1026,12 @@ xfs_rtalloc_query_range(
    if (low_rec->ar_startext >= mp->m_sb.sb_rextents ||
    low_rec->ar_startext == high_rec->ar_startext)
    return 0;
    - if (high_rec->ar_startext > mp->m_sb.sb_rextents)
    - high_rec->ar_startext = mp->m_sb.sb_rextents;
    + high_rec->ar_startext = min(high_rec->ar_startext,
    + mp->m_sb.sb_rextents - 1);

    /* Iterate the bitmap, looking for discrepancies. */
    rtstart = low_rec->ar_startext;
    - rem = high_rec->ar_startext - rtstart;
    - while (rem) {
    + while (rtstart <= high_rec->ar_startext) {
    /* Is the first block free? */
    error = xfs_rtcheck_range(mp, tp, rtstart, 1, 1, &rtend,
    &is_free);
    @@ -1042,7 +1040,7 @@ xfs_rtalloc_query_range(

    /* How long does the extent go for? */
    error = xfs_rtfind_forw(mp, tp, rtstart,
    - high_rec->ar_startext - 1, &rtend);
    + high_rec->ar_startext, &rtend);
    if (error)
    break;

    @@ -1055,7 +1053,6 @@ xfs_rtalloc_query_range(
    break;
    }

    - rem -= rtend - rtstart + 1;
    rtstart = rtend + 1;
    }

    --
    2.25.1


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