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authorLi Zhong <zhong@linux.vnet.ibm.com>2012-07-24 15:02:49 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-10-02 09:47:41 -0700
commit45516ddc16abc923104d78bb3eb772ac0a09e33e (patch)
tree0fa8cea55fecdc0fbaef63165ca4080382f98b93 /kernel
parentb64295e8b4d340a136f02f08baffa9efc0f2e0bc (diff)
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 <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> Tested-by: Christian Kujau <lists@nerdbynature.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Dan Williams <dan.j.williams@gmail.com> Cc: Christian Kujau <lists@nerdbynature.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Cong Wang <xiyou.wangcong@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/async.c13
1 files changed, 9 insertions, 4 deletions
diff --git a/kernel/async.c b/kernel/async.c
index cd9dbb913c77..04f66e328261 100644
--- a/kernel/async.c
+++ b/kernel/async.c
@@ -87,6 +87,13 @@ 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