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    SubjectRe: [PATCH] lock assertion macros for 2.5.31
    Jesse Barnes wrote:
    > On Mon, Aug 12, 2002 at 04:12:41PM -0700, Andrew Morton wrote:
    > > ...
    > > #define might_sleep() BUG_ON(preempt_count())
    > >
    > > _this_ would catch numerous bugs, including code which is not buggy
    > > in 2.4, but became buggy when wild-eyed loonies changed core kernel
    > > rules without even looking at what drivers were doing (rant).
    > >
    > > I expect something like this will fall out of the wash soon, at
    > > least for preemptible kernels.
    > Is it really that simple?

    It sure is:

    * in_atomic_region() - determine whether it is legal to perform a context
    * switch
    * The in_atomic_region() predicate returns true if the current task is
    * executing atomically, and may not perform a context switch.
    * If preemption is enabled, in_atomic_region() is most accurate, because it
    * returns true if this task has taken any spinlocks.
    * If preemption is disabled then there is no spinlocking record available, and
    * we can only look at the interrupt state.
    * If the task has taken a lock_kernel() then it is still legal to perform a
    * context switch.
    #define in_atomic_region() (preempt_count() - !!(current->lock_depth + 1))
    #define in_atomic_region() in_interrupt()

    * may_sleep() - debugging check for possible illegal scheduling.
    * may_sleep() is to be used in code paths which _may_ perform a context switch.
    * It will force a BUG if the caller is executing in an atomic region.
    extern void __in_atomic_region(char *file, int line);
    #define may_sleep() \
    do { \
    if (in_atomic_region()) \
    __in_atomic_region(__FILE__, __LINE__); \
    } while (0)

    > Maybe it should go into sched.h sometime
    > soon? I guess the real work is sprinkling it in all the places where
    > it needs to go.

    Well I added checks just to kmalloc, kmem_cache_alloc, __alloc_pages
    and saw a shower of bloopers during bootup. Such as drivers/ide/probe.c:init_irq()
    calling request_irq() inside ide_lock.

    > Anyway, here's an updated version of the lock assertion patch.

    Well I like it. It's unintrusive, imparts useful info to the reader
    and checks stuff at runtime.

    > Should
    > it be split into two patches, one that implements the macros and
    > another that puts checks everywhere?

    I don't think it needs splitting. You have the core infrastructure plus
    a couple of example applications.

    > Should I add a small doc to
    > Documentation/ (maybe the might_sleep() could be documented there
    > too)?

    These things are self-evident and even self-checking. They don't need
    supporting documentation. I'll put out a test tree RSN, include this
    in it.
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