RDMA/ucma: Remove unnecessary locking of file->ctx_list in close

During the file_operations release function it is already not possible
that write() can be running concurrently, remove the extra locking
around the ctx_list.

Link: https://lore.kernel.org/r/20200818120526.702120-3-leon@kernel.org
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

diff --git a/drivers/infiniband/core/ucma.c b/drivers/infiniband/core/ucma.c
index 6251685..9b019f3 100644 (file)
--- a/drivers/infiniband/core/ucma.c
+++ b/drivers/infiniband/core/ucma.c
@@ -1824,12 +1824,17 @@ static int ucma_close(struct inode *inode, struct file *filp)
        struct ucma_file *file = filp->private_data;
        struct ucma_context *ctx, *tmp;
 
-       mutex_lock(&file->mut);
+       /*
+        * ctx_list can only be mutated under the write(), which is no longer
+        * possible, so no locking needed.
+        */
        list_for_each_entry_safe(ctx, tmp, &file->ctx_list, list) {
+               xa_erase(&ctx_table, ctx->id);
+
+               mutex_lock(&file->mut);
                ctx->destroying = 1;
                mutex_unlock(&file->mut);
 
-               xa_erase(&ctx_table, ctx->id);
                flush_workqueue(file->close_wq);
                /* At that step once ctx was marked as destroying and workqueue
                 * was flushed we are safe from any inflights handlers that
@@ -1849,9 +1854,7 @@ static int ucma_close(struct inode *inode, struct file *filp)
                }
 
                ucma_free_ctx(ctx);
-               mutex_lock(&file->mut);
        }
-       mutex_unlock(&file->mut);
        destroy_workqueue(file->close_wq);
        kfree(file);
        return 0;