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    SubjectRe: [PATCH] Prevent crash on missing sysfs attribute group

    * Eric W. Biederman <> wrote:

    > > Huh, so put repeated, duplicated, inconsistently applied sanity
    > > checks into dozens of sysfs attribute using kernel subsystems?
    > [...]
    > No. I was not talking about every usage site.

    Note, I'm not arguing that this isn't a bug in the P4 PMU driver
    - it is clearly a bug and I've applied the fix for it. I'm
    arguing about the escallation vector that this bug takes - that
    is unnecessarily disruptive:

    You were talking about:

    > >> FIX perf to include sanity checks.

    and what the PMU drivers do here is not uncommon at all, and the
    bug (for which I applied the fix and will push to Linus ASAP) is
    not uncommon either:

    Bugs happen and indirections happen too. perf uses a generic PMU
    driver layer where the lower level layers register themselves.
    There's at least a dozen similar constructs in the kernel and
    you suggest that the right solution is to put checks in every
    one of them, while the nice patch from Bruno could catch it too,
    in one central place?

    If the PMU code used those attributes directly and could
    crash/misbehave then you'd have a point. But the first thing
    that makes real use of these objects is sysfs - so it's
    trivially useful to at minimum have a sanity check there...

    > [...] I was talking about the sites that are don't have a
    > direct call chain to the sysfs methods and instead do
    > something clever that makes backtraces worthless.
    > In the normal case sysfs registration problems are simple to
    > trace back to their source because the backtrace points a
    > finger at the piece of code that when registering had a
    > problem.

    You mean the crash backtrace?

    I don't think we should spuriously crash the kernel on NULL
    pointer input to generic facilities, especially when a check is
    so simple and would catch so many similar patterns of bugs.

    That lack of a check escallated a simple missing (and
    unimportant) attribute into a "box won't boot at all" bug.
    *That* is not acceptable behavior and robustness from a generic
    facility, in my book.

    In that sense the crash behaves like a BUG_ON().



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