loop: Use pr_warn_once() for loop_control_remove() warning

kernel test robot reported that RCU stall via printk() flooding is
possible [1] when stress testing.

Link: https://lkml.kernel.org/r/20211129073709.GA18483@xsang-OptiPlex-9020
Reported-by: kernel test robot <oliver.sang@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index a154cab..c3a36cf 100644 (file)
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -2103,7 +2103,7 @@ static int loop_control_remove(int idx)
        int ret;
 
        if (idx < 0) {
-               pr_warn("deleting an unspecified loop device is not supported.\n");
+               pr_warn_once("deleting an unspecified loop device is not supported.\n");
                return -EINVAL;
        }