diff options
author | José Pekkarinen <jose.pekkarinen@nokia.com> | 2015-10-09 08:42:44 +0300 |
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committer | José Pekkarinen <jose.pekkarinen@nokia.com> | 2015-10-09 08:52:35 +0300 |
commit | fdb8b20906f3546ba6c2f9f0686d8a5189516ba3 (patch) | |
tree | 6bb43dc8a42d6e9403763bc749f706939dd2bc60 /kernel/ipc/sem.c | |
parent | cc84a1f21026270463b580f2564f9d71912b20db (diff) |
Kernel bump from 4.1.3-rt to 4.1.7-rt.
These changes brings a vanilla kernel from kernel.org, and the patch
applied for rt is patch-4.1.7-rt8.patch. No further changes needed.
Change-Id: Id8dd03c2ddd971e4d1d69b905f3069737053b700
Signed-off-by: José Pekkarinen <jose.pekkarinen@nokia.com>
Diffstat (limited to 'kernel/ipc/sem.c')
-rw-r--r-- | kernel/ipc/sem.c | 41 |
1 files changed, 31 insertions, 10 deletions
diff --git a/kernel/ipc/sem.c b/kernel/ipc/sem.c index 8f99bac19..d6261bef5 100644 --- a/kernel/ipc/sem.c +++ b/kernel/ipc/sem.c @@ -253,6 +253,16 @@ static void sem_rcu_free(struct rcu_head *head) } /* + * spin_unlock_wait() and !spin_is_locked() are not memory barriers, they + * are only control barriers. + * The code must pair with spin_unlock(&sem->lock) or + * spin_unlock(&sem_perm.lock), thus just the control barrier is insufficient. + * + * smp_rmb() is sufficient, as writes cannot pass the control barrier. + */ +#define ipc_smp_acquire__after_spin_is_unlocked() smp_rmb() + +/* * Wait until all currently ongoing simple ops have completed. * Caller must own sem_perm.lock. * New simple ops cannot start, because simple ops first check @@ -275,6 +285,7 @@ static void sem_wait_array(struct sem_array *sma) sem = sma->sem_base + i; spin_unlock_wait(&sem->lock); } + ipc_smp_acquire__after_spin_is_unlocked(); } /* @@ -327,13 +338,12 @@ static inline int sem_lock(struct sem_array *sma, struct sembuf *sops, /* Then check that the global lock is free */ if (!spin_is_locked(&sma->sem_perm.lock)) { /* - * The ipc object lock check must be visible on all - * cores before rechecking the complex count. Otherwise - * we can race with another thread that does: + * We need a memory barrier with acquire semantics, + * otherwise we can race with another thread that does: * complex_count++; * spin_unlock(sem_perm.lock); */ - smp_rmb(); + ipc_smp_acquire__after_spin_is_unlocked(); /* * Now repeat the test of complex_count: @@ -2084,17 +2094,28 @@ void exit_sem(struct task_struct *tsk) rcu_read_lock(); un = list_entry_rcu(ulp->list_proc.next, struct sem_undo, list_proc); - if (&un->list_proc == &ulp->list_proc) - semid = -1; - else - semid = un->semid; + if (&un->list_proc == &ulp->list_proc) { + /* + * We must wait for freeary() before freeing this ulp, + * in case we raced with last sem_undo. There is a small + * possibility where we exit while freeary() didn't + * finish unlocking sem_undo_list. + */ + spin_unlock_wait(&ulp->lock); + rcu_read_unlock(); + break; + } + spin_lock(&ulp->lock); + semid = un->semid; + spin_unlock(&ulp->lock); + /* exit_sem raced with IPC_RMID, nothing to do */ if (semid == -1) { rcu_read_unlock(); - break; + continue; } - sma = sem_obtain_object_check(tsk->nsproxy->ipc_ns, un->semid); + sma = sem_obtain_object_check(tsk->nsproxy->ipc_ns, semid); /* exit_sem raced with IPC_RMID, nothing to do */ if (IS_ERR(sma)) { rcu_read_unlock(); |