mmc: fix a deadlock between system suspend and MMC block IO

Performing MMC block IO with simultaneous STR can lead to a deadlock: the
mmc_pm_notify() function claims the host and then calls bus .remove()
method, which lands in mmc_blk_remove(), which calls mmc_blk_remove_req()
then it goes to -> mmc_cleanup_queue() -> kthread_stop(), which waits for
the mmc-block thread to stop. If the mmc-block thread at that time is
processing block requests, it will also try to claim the host in
mmc_blk_issue_rq() and block there. This patch fixes the problem by
calling .remove() before claiming the host.
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: Arindam Nath <arindam.nath@amd.com>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/core/core.c

@@ -2175,6 +2175,7 @@ void mmc_stop_host(struct mmc_host *host)
 
 	mmc_bus_get(host);
 	if (host->bus_ops && !host->bus_dead) {
+		/* Calling bus_ops->remove() with a claimed host can deadlock */
 		if (host->bus_ops->remove)
 			host->bus_ops->remove(host);
 
@@ -2398,7 +2399,9 @@ int mmc_suspend_host(struct mmc_host *host)
 			if (err == -ENOSYS || !host->bus_ops->resume) {
 				/*
 				 * We simply "remove" the card in this case.
-				 * It will be redetected on resume.
+				 * It will be redetected on resume.  (Calling
+				 * bus_ops->remove() with a claimed host can
+				 * deadlock.)
 				 */
 				if (host->bus_ops->remove)
 					host->bus_ops->remove(host);
@@ -2491,11 +2494,11 @@ int mmc_pm_notify(struct notifier_block *notify_block,
 		if (!host->bus_ops || host->bus_ops->suspend)
 			break;
 
-		mmc_claim_host(host);
-
+		/* Calling bus_ops->remove() with a claimed host can deadlock */
 		if (host->bus_ops->remove)
 			host->bus_ops->remove(host);
 
+		mmc_claim_host(host);
 		mmc_detach_bus(host);
 		mmc_power_off(host);
 		mmc_release_host(host);