SUNRPC: Eliminate side effects from rpc_malloc
Currently rpc_malloc sets req->rq_buffer internally. Make this a more
generic interface: return a pointer to the new buffer (or NULL) and
make the caller set req->rq_buffer and req->rq_bufsize. This looks much
more like kmalloc and eliminates the side effects.
To fix a potential deadlock, this patch also replaces GFP_NOFS with
GFP_NOWAIT in rpc_malloc. This prevents async RPCs from sleeping outside
the RPC's task scheduler while allocating their buffer.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c
index 6d87320..4a53e94 100644
--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -741,50 +741,53 @@
* @task: RPC task that will use this buffer
* @size: requested byte size
*
- * We try to ensure that some NFS reads and writes can always proceed
- * by using a mempool when allocating 'small' buffers.
+ * To prevent rpciod from hanging, this allocator never sleeps,
+ * returning NULL if the request cannot be serviced immediately.
+ * The caller can arrange to sleep in a way that is safe for rpciod.
+ *
+ * Most requests are 'small' (under 2KiB) and can be serviced from a
+ * mempool, ensuring that NFS reads and writes can always proceed,
+ * and that there is good locality of reference for these buffers.
+ *
* In order to avoid memory starvation triggering more writebacks of
- * NFS requests, we use GFP_NOFS rather than GFP_KERNEL.
+ * NFS requests, we avoid using GFP_KERNEL.
*/
-void * rpc_malloc(struct rpc_task *task, size_t size)
+void *rpc_malloc(struct rpc_task *task, size_t size)
{
- struct rpc_rqst *req = task->tk_rqstp;
- gfp_t gfp;
+ size_t *buf;
+ gfp_t gfp = RPC_IS_SWAPPER(task) ? GFP_ATOMIC : GFP_NOWAIT;
- if (task->tk_flags & RPC_TASK_SWAPPER)
- gfp = GFP_ATOMIC;
+ size += sizeof(size_t);
+ if (size <= RPC_BUFFER_MAXSIZE)
+ buf = mempool_alloc(rpc_buffer_mempool, gfp);
else
- gfp = GFP_NOFS;
-
- if (size > RPC_BUFFER_MAXSIZE) {
- req->rq_buffer = kmalloc(size, gfp);
- if (req->rq_buffer)
- req->rq_bufsize = size;
- } else {
- req->rq_buffer = mempool_alloc(rpc_buffer_mempool, gfp);
- if (req->rq_buffer)
- req->rq_bufsize = RPC_BUFFER_MAXSIZE;
- }
- return req->rq_buffer;
+ buf = kmalloc(size, gfp);
+ *buf = size;
+ dprintk("RPC: %5u allocated buffer of size %u at %p\n",
+ task->tk_pid, size, buf);
+ return (void *) ++buf;
}
/**
* rpc_free - free buffer allocated via rpc_malloc
- * @task: RPC task with a buffer to be freed
+ * @buffer: buffer to free
*
*/
-void rpc_free(struct rpc_task *task)
+void rpc_free(void *buffer)
{
- struct rpc_rqst *req = task->tk_rqstp;
+ size_t size, *buf = (size_t *) buffer;
- if (req->rq_buffer) {
- if (req->rq_bufsize == RPC_BUFFER_MAXSIZE)
- mempool_free(req->rq_buffer, rpc_buffer_mempool);
- else
- kfree(req->rq_buffer);
- req->rq_buffer = NULL;
- req->rq_bufsize = 0;
- }
+ if (!buffer)
+ return;
+ size = *buf;
+ buf--;
+
+ dprintk("RPC: freeing buffer of size %u at %p\n",
+ size, buf);
+ if (size <= RPC_BUFFER_MAXSIZE)
+ mempool_free(buf, rpc_buffer_mempool);
+ else
+ kfree(buf);
}
/*