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    SubjectRE: [PATCH v1] mm/gup: fix FOLL_FORCE COW security issue and remove FOLL_COW
    Date
    From: Jason Gunthorpe
    > Sent: 09 August 2022 20:08
    >
    > On Tue, Aug 09, 2022 at 11:59:45AM -0700, Linus Torvalds wrote:
    >
    > > But as a very good approximation, the rule is "absolutely no new
    > > BUG_ON() calls _ever_". Because I really cannot see a single case
    > > where "proper error handling and WARN_ON_ONCE()" isn't the right
    > > thing.
    >
    > Parallel to this discussion I've had ones where people more or less
    > say
    >
    > Since BUG_ON crashes the machine and Linus says that crashing the
    > machine is bad, WARN_ON will also crash the machine if you set the
    > panic_on_warn parameter, so it is also bad, thus we shouldn't use
    > anything.
    >
    > I've generally maintained that people who set the panic_on_warn *want*
    > these crashes, because that is the entire point of it. So we should
    > use WARN_ON with an error recovery for "can't happen" assertions like
    > these. I think it is what you are saying here.

    They don't necessarily want the crashes, it is more the people who
    built the distribution think they want the crashes.

    I have had issues with a customer system (with our drivers) randomly
    locking up.
    Someone had decided that 'PANIC_ON_OOPS' was a good idea but hadn't
    enabled anything to actually take the dump.

    So instead of a diagnosable problem (and a 'doh' moment) you
    get several weeks of head scratching and a very annoyed user.

    David

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