• Stephen Frost's avatar
    Skip dead backends in MinimumActiveBackends · 1bf4a84d
    Stephen Frost authored
    Back in ed0b409d, PGPROC was split and moved to static variables in
    procarray.c, with procs in ProcArrayStruct replaced by an array of
    integers representing process numbers (pgprocnos), with -1 indicating a
    dead process which has yet to be removed.  Access to procArray is
    generally done under ProcArrayLock and therefore most code does not have
    to concern itself with -1 entries.
    
    However, MinimumActiveBackends intentionally does not take
    ProcArrayLock, which means it has to be extra careful when accessing
    procArray.  Prior to ed0b409d, this was handled by checking for a NULL
    in the pointer array, but that check was no longer valid after the
    split.  Coverity pointed out that the check could never happen and so
    it was removed in 5592ebac.  That didn't make anything worse, but it
    didn't fix the issue either.
    
    The correct fix is to check for pgprocno == -1 and skip over that entry
    if it is encountered.
    
    Back-patch to 9.2, since there can be attempts to access the arrays
    prior to their start otherwise.  Note that the changes prior to 9.4 will
    look a bit different due to the change in 5592ebac.
    
    Note that MinimumActiveBackends only returns a bool for heuristic
    purposes and any pre-array accesses are strictly read-only and so there
    is no security implication and the lack of fields complaints indicates
    it's very unlikely to run into issues due to this.
    
    Pointed out by Noah.
    1bf4a84d
procarray.c 112 KB