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    SubjectRe: [PATCH] kernel:async function call:introduce async_run_inatomic(v2)
    On Wed, 13 May 2009 23:51:39 +0800,
    tom.leiming@gmail.com wrote:

    > From: Ming Lei <tom.leiming@gmail.com>
    >
    > The purpose of this function is to offer a simple way to schedule an
    > asynchronous thread from an atomic context, because there are not any
    > functions which can create and start a kernel thread in atomic contexts
    > now. We use async_running_no_sync as running list to make callers that
    > don't want to synchronize on cookies, so can avoid some side effects for
    > async_synchronize_full().
    >
    > Part of note for async_run_inatomic and some guideline is from Cornelia Huck.
    >
    > Signed-off-by: Ming Lei <tom.leiming@gmail.com>
    > Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
    > ---
    > include/linux/async.h | 2 ++
    > kernel/async.c | 23 +++++++++++++++++++++++
    > 2 files changed, 25 insertions(+), 0 deletions(-)
    >
    > diff --git a/include/linux/async.h b/include/linux/async.h
    > index 18ce92b..9ff62af 100644
    > --- a/include/linux/async.h
    > +++ b/include/linux/async.h
    > @@ -16,6 +16,8 @@
    > typedef u64 async_cookie_t;
    > typedef void (async_func_ptr) (void *data, async_cookie_t cookie);
    >
    > +extern int async_run_inatomic(async_func_ptr *ptr, void *data);
    > +
    > extern async_cookie_t async_schedule(async_func_ptr *ptr, void *data);
    > extern async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data,
    > struct list_head *list);
    > diff --git a/kernel/async.c b/kernel/async.c
    > index 8663f5b..cb527b3 100644
    > --- a/kernel/async.c
    > +++ b/kernel/async.c
    > @@ -65,6 +65,7 @@ static async_cookie_t next_cookie = 1;
    >
    > static LIST_HEAD(async_pending);
    > static LIST_HEAD(async_running);
    > +static LIST_HEAD(async_running_no_sync);
    > static DEFINE_SPINLOCK(async_lock);
    >
    > static int async_enabled = 0;
    > @@ -222,6 +223,28 @@ static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data,
    > return newcookie;
    > }
    >
    > + /**
    > + * async_run_inatomic - in atomic contexts schedule a function for
    > + * asynchronous execution

    I'm not 100% sure whether kerneldoc likes split lines for the
    description.

    "async_run_inatomic - schedule a function for asynchronous execution from atomic context without checkpointing"
    - but that's really a bit long...

    > + *
    > + * @ptr: function to execute asynchronously
    > + * @data: data pointer to pass to the function
    > + *
    > + * Return zero if success, or else return others if failured

    Returns zero on success, !zero on failure

    > + * Note:

    I'd move the description of the function's purpose before Note:.

    > + * The purpose of this function is to offer a simple way to schedule an
    > + * asynchronous thread from an atomic context, because there are not any
    > + * functions which can create and start a kernel thread in atomic contexts
    > + * now.

    I don't think the second part of the sentence is needed, this should
    only be mentioned in the patch description. I'd rather add

    "Since it does not return a cookie for checkpointing, it is for callers
    that don't need later synchronization."

    > We use async_running_no_sync as running list to make callers that
    > + * don't want to synchronize on cookies, so can avoid some side effects for
    > + * async_synchronize_full().

    "async_run_inatomic() uses a distinct running list in order to avoid
    slowing down synchronization within the general domain."

    (The cookie will still be checked when __lowest_in_progress() returns
    the cookie for the async_pending list, but I think that is negligible -
    and it would be a general issue for special domains.)

    > + */
    > +int async_run_inatomic(async_func_ptr *ptr, void *data)
    > +{
    > + return !__async_schedule(ptr, data, &async_running_no_sync, 1);
    > +}
    > +EXPORT_SYMBOL_GPL(async_run_inatomic);
    > +
    > /**
    > * async_schedule - schedule a function for asynchronous execution
    > * @ptr: function to execute asynchronously

    Btw: Do you have any specific use cases for this function in mind?


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