release/5.2.27/nbd-protect-cmd-status-with-cmd-lock.patch

From 5d6e015cded59f747c67ca31a95adc2e8e407b50 Mon Sep 17 00:00:00 2001
From: Josef Bacik <josef@toxicpanda.com>
Date: Mon, 21 Oct 2019 15:56:27 -0400
Subject: [PATCH] nbd: protect cmd->status with cmd->lock

commit de6346ecbc8f5591ebd6c44ac164e8b8671d71d7 upstream.

We already do this for the most part, except in timeout and clear_req.
For the timeout case we take the lock after we grab a ref on the config,
but that isn't really necessary because we're safe to touch the cmd at
this point, so just move the order around.

For the clear_req cause this is initiated by the user, so again is safe.

Reviewed-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 6b91b1b95ef0..76c04edb1b67 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -349,17 +349,16 @@ static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req,
 	struct nbd_device *nbd = cmd->nbd;
 	struct nbd_config *config;
 
+	if (!mutex_trylock(&cmd->lock))
+		return BLK_EH_RESET_TIMER;
+
 	if (!refcount_inc_not_zero(&nbd->config_refs)) {
 		cmd->status = BLK_STS_TIMEOUT;
+		mutex_unlock(&cmd->lock);
 		goto done;
 	}
 	config = nbd->config;
 
-	if (!mutex_trylock(&cmd->lock)) {
-		nbd_config_put(nbd);
-		return BLK_EH_RESET_TIMER;
-	}
-
 	if (config->num_connections > 1) {
 		dev_err_ratelimited(nbd_to_dev(nbd),
 				    "Connection timed out, retrying (%d/%d alive)\n",
@@ -753,7 +752,10 @@ static bool nbd_clear_req(struct request *req, void *data, bool reserved)
 {
 	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);
 
+	mutex_lock(&cmd->lock);
 	cmd->status = BLK_STS_IOERR;
+	mutex_unlock(&cmd->lock);
+
 	blk_mq_complete_request(req);
 	return true;
 }
-- 
2.7.4