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| author | Paolo Bonzini <pbonzini@redhat.com> | 2016-07-15 20:58:41 +0300 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2016-08-02 12:03:58 +0200 |
| commit | 34506b30e4210b417aa38d1518aa2c53fb7cf39b (patch) | |
| tree | eb3653db2474e880a5735baebe8c83a6d395f572 /util | |
| parent | cc0100f464c94bf80ad36cd432f4a1ed58126b60 (diff) | |
| download | qemu-34506b30e4210b417aa38d1518aa2c53fb7cf39b.tar.gz | |
util/qht: Document memory ordering assumptions
It is naturally expected that some memory ordering should be provided
around qht_insert() and qht_lookup(). Document these assumptions in the
header file and put some comments in the source to denote how that
memory ordering requirements are fulfilled.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[Sergey Fedorov: commit title and message provided;
comment on qht_remove() elided]
Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
Message-Id: <20160715175852.30749-2-sergey.fedorov@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'util')
| -rw-r--r-- | util/qht.c | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/util/qht.c b/util/qht.c index 40d6e218f7..28ce289245 100644 --- a/util/qht.c +++ b/util/qht.c @@ -445,7 +445,11 @@ void *qht_do_lookup(struct qht_bucket *head, qht_lookup_func_t func, do { for (i = 0; i < QHT_BUCKET_ENTRIES; i++) { if (b->hashes[i] == hash) { - void *p = atomic_read(&b->pointers[i]); + /* The pointer is dereferenced before seqlock_read_retry, + * so (unlike qht_insert__locked) we need to use + * atomic_rcu_read here. + */ + void *p = atomic_rcu_read(&b->pointers[i]); if (likely(p) && likely(func(p, userp))) { return p; @@ -535,6 +539,7 @@ static bool qht_insert__locked(struct qht *ht, struct qht_map *map, atomic_rcu_set(&prev->next, b); } b->hashes[i] = hash; + /* smp_wmb() implicit in seqlock_write_begin. */ atomic_set(&b->pointers[i], p); seqlock_write_end(&head->sequence); return true; |