diff options
| author | David S. Miller <davem@davemloft.net> | 2016-05-04 00:52:29 -0400 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2016-05-04 00:52:29 -0400 |
| commit | cba653210056cf47cc1969f831f05ddfb99ee2bd (patch) | |
| tree | 92d93a3eee5b12d77af3696b9da8026e71df5752 /kernel/workqueue.c | |
| parent | 26879da58711aa604a1b866cbeedd7e0f78f90ad (diff) | |
| parent | 7391daf2ffc780679d6ab3fad1db2619e5dd2c2a (diff) | |
Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
Conflicts:
net/ipv4/ip_gre.c
Minor conflicts between tunnel bug fixes in net and
ipv6 tunnel cleanups in net-next.
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'kernel/workqueue.c')
| -rw-r--r-- | kernel/workqueue.c | 29 |
1 files changed, 29 insertions, 0 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 2232ae3e3ad6..3bfdff06eea7 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -666,6 +666,35 @@ static void set_work_pool_and_clear_pending(struct work_struct *work, */ smp_wmb(); set_work_data(work, (unsigned long)pool_id << WORK_OFFQ_POOL_SHIFT, 0); + /* + * The following mb guarantees that previous clear of a PENDING bit + * will not be reordered with any speculative LOADS or STORES from + * work->current_func, which is executed afterwards. This possible + * reordering can lead to a missed execution on attempt to qeueue + * the same @work. E.g. consider this case: + * + * CPU#0 CPU#1 + * ---------------------------- -------------------------------- + * + * 1 STORE event_indicated + * 2 queue_work_on() { + * 3 test_and_set_bit(PENDING) + * 4 } set_..._and_clear_pending() { + * 5 set_work_data() # clear bit + * 6 smp_mb() + * 7 work->current_func() { + * 8 LOAD event_indicated + * } + * + * Without an explicit full barrier speculative LOAD on line 8 can + * be executed before CPU#0 does STORE on line 1. If that happens, + * CPU#0 observes the PENDING bit is still set and new execution of + * a @work is not queued in a hope, that CPU#1 will eventually + * finish the queued @work. Meanwhile CPU#1 does not see + * event_indicated is set, because speculative LOAD was executed + * before actual STORE. + */ + smp_mb(); } static void clear_work_data(struct work_struct *work) |