From 11266a8e031a3782241760850f002c79ee2887e1 Mon Sep 17 00:00:00 2001 From: Li Zhong Date: Tue, 24 Jul 2012 15:02:49 -0700 Subject: [PATCH] Fix a dead loop in async_synchronize_full() [Fixed upstream by commits 2955b47d2c1983998a8c5915cb96884e67f7cb53 and a4683487f90bfe3049686fc5c566bdc1ad03ace6 from Dan Williams, but they are much more intrusive than this tiny fix, according to Andrew - gregkh] 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. 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 Signed-off-by: Li Zhong Tested-by: Paul E. McKenney Tested-by: Christian Kujau Cc: Andrew Morton Cc: Dan Williams Cc: Christian Kujau Cc: Andrew Morton Cc: Cong Wang Signed-off-by: Greg Kroah-Hartman --- kernel/async.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/kernel/async.c b/kernel/async.c index bd0c168a3bbe..32d8dc960263 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 -- 2.39.5