• Russ Cox's avatar
    runtime: fix sudog leak · b3932bab
    Russ Cox authored
    The SudoG used to sit on the stack, so it was cheap to allocated
    and didn't need to be cleaned up when finished.
    
    For the conversion to Go, we had to move sudog off the stack
    for a few reasons, so we added a cache of recently used sudogs
    to keep allocation cheap. But we didn't add any of the necessary
    cleanup before adding a SudoG to the new cache, and so the cached
    SudoGs had stale pointers inside them that have caused all sorts
    of awful, hard to debug problems.
    
    CL 155760043 made sure SudoG.elem is cleaned up.
    CL 150520043 made sure SudoG.selectdone is cleaned up.
    
    This CL makes sure SudoG.next, SudoG.prev, and SudoG.waitlink
    are cleaned up. I should have done this when I did the other two
    fields; instead I wasted a week tracking down a leak they caused.
    
    A dangling SudoG.waitlink can point into a sudogcache list that
    has been "forgotten" in order to let the GC collect it, but that
    dangling .waitlink keeps the list from being collected.
    And then the list holding the SudoG with the dangling waitlink
    can find itself in the same situation, and so on. We end up
    with lists of lists of unusable SudoGs that are still linked into
    the object graph and never collected (given the right mix of
    non-trivial selects and non-channel synchronization).
    
    More details in golang.org/issue/9110.
    
    Fixes #9110.
    
    LGTM=r
    R=r
    CC=dvyukov, golang-codereviews, iant, khr
    https://golang.org/cl/177870043
    b3932bab
sema.go 5.62 KB