Fix a dead loop in async_synchronize_full()
[Fixed upstream by commits2955b47d2c
anda4683487f9
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>
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@ -86,6 +86,13 @@ static async_cookie_t __lowest_in_progress(struct list_head *running)
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{
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struct async_entry *entry;
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if (!running) { /* just check the entry count */
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if (atomic_read(&entry_count))
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return 0; /* smaller than any cookie */
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else
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return next_cookie;
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}
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if (!list_empty(running)) {
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entry = list_first_entry(running,
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struct async_entry, list);
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@ -236,9 +243,7 @@ EXPORT_SYMBOL_GPL(async_schedule_domain);
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*/
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void async_synchronize_full(void)
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{
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do {
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async_synchronize_cookie(next_cookie);
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} while (!list_empty(&async_running) || !list_empty(&async_pending));
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async_synchronize_cookie_domain(next_cookie, NULL);
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}
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EXPORT_SYMBOL_GPL(async_synchronize_full);
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@ -258,7 +263,7 @@ EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
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/**
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* async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
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* @cookie: async_cookie_t to use as checkpoint
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* @running: running list to synchronize on
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* @running: running list to synchronize on, NULL indicates all lists
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*
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* This function waits until all asynchronous function calls for the
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* synchronization domain specified by the running list @list submitted
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