• Austin Clements's avatar
    runtime: fix check for vacuous page boundary rounding · 336dad2a
    Austin Clements authored
    sysUnused (e.g., madvise MADV_FREE) is only sensible to call on
    physical page boundaries, so scavengelist rounds in the bounds of the
    region being released to the nearest physical page boundaries.
    However, if the region is smaller than a physical page and neither the
    start nor end fall on a boundary, then rounding the start up to a page
    boundary and the end down to a page boundary will result in end < start.
    Currently, we only give up on the region if start == end, so if we
    encounter end < start, we'll call madvise with a negative length and
    the madvise will fail.
    
    Issue #16644 gives a concrete example of this:
    
        start = 0x1285ac000
        end   = 0x1285ae000 (1 8K page)
    
    This leads to the rounded values
    
        start = 0x1285b0000
        end   = 0x1285a0000
    
    which leads to len = -65536.
    
    Fix this by giving up on the region if end <= start, not just if
    end == start.
    
    Fixes #16644.
    
    Change-Id: I8300db492dbadc82ac1ad878318b36bcb7c39524
    Reviewed-on: https://go-review.googlesource.com/27230Reviewed-by: 's avatarKeith Randall <khr@golang.org>
    336dad2a
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