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    SubjectRe: [PATCH 1/3][-mm] add class_reclassify macro
    On Tue, May 20, 2008 at 6:02 PM, Andrew Morton
    <akpm@linux-foundation.org> wrote:
    > On Tue, 20 May 2008 17:55:54 +0800 Dave Young <hidave.darkstar@gmail.com> wrote:
    >
    >> Converting class semaphore to mutex cause lockdep warnings due to
    >> class_interface_register/unregister will possible call device_add/del
    >
    > Shouldn't we just fix that?

    Andrew, could you tell more?

    >
    >> For the class_interface users here add a class_reclassify macro to
    >> reclassify the lock class of their struct class.
    >>
    >> Signed-off-by: Dave Young <hidave.darkstar@gmail.com>
    >>
    >> ---
    >> include/linux/device.h | 7 +++++++
    >> 1 file changed, 7 insertions(+)
    >>
    >> --- linux/include/linux/device.h 2008-05-19 12:29:54.000000000 +0800
    >> +++ linux.new/include/linux/device.h 2008-05-19 14:42:25.000000000 +0800
    >> @@ -529,4 +529,11 @@ extern const char *dev_driver_string(str
    >> MODULE_ALIAS("char-major-" __stringify(major) "-" __stringify(minor))
    >> #define MODULE_ALIAS_CHARDEV_MAJOR(major) \
    >> MODULE_ALIAS("char-major-" __stringify(major) "-*")
    >> +
    >> +#define class_reclassify(class) \
    >> +do { \
    >> + static struct lock_class_key class_key; \
    >> + lockdep_set_class_and_name(&(class)->mutex, &class_key, \
    >> + (class)->name); \
    >> +} while (0)
    >> #endif /* _DEVICE_H_ */
    >
    > I think it would need a lavish comment explaining what it is for, and
    > the reasons for its existence.

    Yes, will do.

    >
    > Perhaps this should be a kernel-wide thing in lockdep.h. But then that
    > would invite people to use it, and it looks like a bad thing.

    I agree.
    There's wellmeant lockdep warnings for some safe code logic every some time.
    Yes, this macro violates the lockdep class-based rules, but it can act
    as just supplementary. And it could help some users.

    >
    > device.h does not include lockdep.h, so putting this here assumes that
    > callees have already included lockdep.h. This is the sort of
    > assumption which leads to compilation errors.
    >
    My wrong, thanks.

    Regards
    dave


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