motorhead/qemu
1
0
Fork 0
mirror of https://github.com/Motorhead1991/qemu.git synced 2025-08-05 00:33:55 -06:00
Code Issues Projects Releases Packages Wiki Activity Actions

util/qht: Document memory ordering assumptions

Browse source 
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>
This commit is contained in:
Paolo Bonzini 2016-07-15 20:58:41 +03:00
parent cc0100f464
commit 34506b30e4
2 changed files with 11 additions and 1 deletions
Download patch file Download diff file Expand all files Collapse all files

7
util/qht.c
View file

@ -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;