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sunrpc/cache: remove races with queuing an upcall. 

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.

Also remove the early 'return' from cache_dequeue() to ensure that it
always removes all entries: As there is no locking between setting
CACHE_PENDING and calling sunrpc_cache_pipe_upcall it is not
inconceivable for some other thread to clear CACHE_PENDING and then
someone else to set it and call sunrpc_cache_pipe_upcall, both before
the original threads completed the call.

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@ts.fujitsu.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Bodo Stroesser <bstroesser@ts.fujitsu.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
This commit is contained in:
NeilBrown 2013-06-13 12:53:42 +10:00 committed by J. Bruce Fields
parent d08d32e6e5
commit f9e1aedc6c
1 changed files with 29 additions and 11 deletions
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40
net/sunrpc/cache.c
View File

@ -1036,23 +1036,32 @@ static int cache_release(struct inode *inode, struct file *filp,
static void cache_dequeue(struct cache_detail *detail, struct cache_head *ch)
{
struct cache_queue *cq;
struct cache_queue *cq, *tmp;
struct cache_request *cr;
struct list_head dequeued;
INIT_LIST_HEAD(&dequeued);
spin_lock(&queue_lock);
list_for_each_entry(cq, &detail->queue, list)
list_for_each_entry_safe(cq, tmp, &detail->queue, list)
if (!cq->reader) {
struct cache_request *cr = container_of(cq, struct cache_request, q);
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);
spin_unlock(&queue_lock);
cache_put(cr->item, detail);
kfree(cr->buf);
kfree(cr);
return;
list_move(&cr->q.list, &dequeued);
}
spin_unlock(&queue_lock);
while (!list_empty(&dequeued)) {
cr = list_entry(dequeued.next, struct cache_request, q.list);
list_del(&cr->q.list);
cache_put(cr->item, detail);
kfree(cr->buf);
kfree(cr);
}
}
/*
@ -1166,6 +1175,7 @@ int sunrpc_cache_pipe_upcall(struct cache_detail *detail, struct cache_head *h)
char *buf;
struct cache_request *crq;
int ret = 0;
if (!detail->cache_request)
return -EINVAL;
@ -1191,10 +1201,18 @@ int sunrpc_cache_pipe_upcall(struct cache_detail *detail, struct cache_head *h)
crq->len = 0;
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);