We currently queue an upcall after setting CACHE_PENDING,
and dequeue after clearing CACHE_PENDING.
So a request should only be present when CACHE_PENDING is set.
However we don't combine the test and the enqueue/dequeue in
a protected region, so it is possible (if unlikely) for a race
to result in a request being queued without CACHE_PENDING set,
or a request to be absent despite CACHE_PENDING.
So: include a test for CACHE_PENDING inside the regions of
enqueue and dequeue where queue_lock is held, and abort
the operation if the value is not as expected.
With this, it perfectly safe and correct to:
- call cache_dequeue() if and only if we have just
cleared CACHE_PENDING
- call sunrpc_cache_pipe_upcall() (via cache_make_upcall)
if and only if we have just set CACHE_PENDING.
Reported-by: Bodo Stroesser <bstroesser@xxxxxxxxxxxxxx>
Signed-off-by: NeilBrown <neilb@xxxxxxx>
---
net/sunrpc/cache.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index 9afa439..b48c8ef 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -1022,6 +1022,9 @@ static void cache_dequeue(struct cache_detail *detail, struct cache_head *ch)
struct cache_request *cr = container_of(cq, struct cache_request, q);
if (cr->item != ch)
continue;
+ if (test_bit(CACHE_PENDING, &ch->flags))
+ /* Lost a race and it is pending again */
+ break;
if (cr->readers != 0)
continue;
list_del(&cr->q.list);
@@ -1151,6 +1154,7 @@ int sunrpc_cache_pipe_upcall(struct cache_detail *detail, struct cache_head *h,
struct cache_request *crq;
char *bp;
int len;
+ int ret = 0;
if (!cache_listeners_exist(detail)) {
warn_no_listener(detail);
@@ -1182,10 +1186,18 @@ int sunrpc_cache_pipe_upcall(struct cache_detail *detail, struct cache_head *h,
crq->len = PAGE_SIZE - len;
crq->readers = 0;
spin_lock(&queue_lock);
- list_add_tail(&crq->q.list, &detail->queue);
+ if (test_bit(CACHE_PENDING, &h->flags))
+ list_add_tail(&crq->q.list, &detail->queue);
+ else
+ /* Lost a race, no longer PENDING, so don't enqueue */
+ ret = -EAGAIN;
spin_unlock(&queue_lock);
wake_up(&queue_wait);
- return 0;
+ if (ret == -EAGAIN) {
+ kfree(buf);
+ kfree(crq);
+ }
+ return ret;
}
EXPORT_SYMBOL_GPL(sunrpc_cache_pipe_upcall);
--
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