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SubjectRe: [PATCH] Fix a dead loop in async_synchronize_full()
On Mon, 2 Jul 2012 at 14:04, Li Zhong wrote:
> This patch tries to fix a dead loop in async_synchronize_full(), which
> could be seen when preemption is disabled on a single cpu machine.

This helps in my case[0], will this patch be included in -rc6?

Thanks,
Christian.

[0] https://lists.ozlabs.org/pipermail/linuxppc-dev/2012-July/098922.html


> void async_synchronize_full(void)
> {
> do {
> async_synchronize_cookie(next_cookie);
> } while (!list_empty(&async_running) || !
> list_empty(&async_pending));
> }
>
> async_synchronize_cookie() calls async_synchronize_cookie_domain() with
> &async_running as the default domain to synchronize.
>
> However, there might be some works in the async_pending list from other
> domains. On a single cpu system, without preemption, there is no chance
> for the other works to finish, so async_synchronize_full() enters a dead
> loop.
>
> It seems async_synchronize_full() wants to synchronize all entries in
> all running lists(domains), so maybe we could just check the entry_count
> to know whether all works are finished.
>
> Currently, async_synchronize_cookie_domain() expects a non-NULL running
> list ( if NULL, there would be NULL pointer dereference ), so maybe a
> NULL pointer could be used as an indication for the functions to
> synchronize all works in all domains.
>
> Reported-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Signed-off-by: Li Zhong <zhong@linux.vnet.ibm.com>
> Tested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> ---
> kernel/async.c | 13 +++++++++----
> 1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/async.c b/kernel/async.c
> index bd0c168..32d8dc9 100644
> --- a/kernel/async.c
> +++ b/kernel/async.c
> @@ -86,6 +86,13 @@ static async_cookie_t __lowest_in_progress(struct
> list_head *running)
> {
> struct async_entry *entry;
>
> + if (!running) { /* just check the entry count */
> + if (atomic_read(&entry_count))
> + return 0; /* smaller than any cookie */
> + else
> + return next_cookie;
> + }
> +
> if (!list_empty(running)) {
> entry = list_first_entry(running,
> struct async_entry, list);
> @@ -236,9 +243,7 @@ EXPORT_SYMBOL_GPL(async_schedule_domain);
> */
> void async_synchronize_full(void)
> {
> - do {
> - async_synchronize_cookie(next_cookie);
> - } while (!list_empty(&async_running) || !list_empty(&async_pending));
> + async_synchronize_cookie_domain(next_cookie, NULL);
> }
> EXPORT_SYMBOL_GPL(async_synchronize_full);
>
> @@ -258,7 +263,7 @@ EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
> /**
> * async_synchronize_cookie_domain - synchronize asynchronous function
> calls within a certain domain with cookie checkpointing
> * @cookie: async_cookie_t to use as checkpoint
> - * @running: running list to synchronize on
> + * @running: running list to synchronize on, NULL indicates all lists
> *
> * This function waits until all asynchronous function calls for the
> * synchronization domain specified by the running list @list submitted
> --
> 1.7.9.5
>
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--
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runaway cat on system.


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