linux-kernel - [PATCH 5.17 180/772] scsi: target: tcmu: Avoid holding XArray lock when calling lock

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Date:   Tue,  7 Jun 2022 18:56:12 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dan Carpenter <dan.carpenter@...cle.com>,
        Bodo Stroesser <bostroesser@...il.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.17 180/772] scsi: target: tcmu: Avoid holding XArray lock when calling lock_page

From: Bodo Stroesser <bostroesser@...il.com>

[ Upstream commit 325d5c5fb216674296f3902a8902b942da3adc5b ]

In tcmu_blocks_release(), lock_page() is called to prevent a race causing
possible data corruption. Since lock_page() might sleep, calling it while
holding XArray lock is a bug.

To fix this, replace the xas_for_each() call with xa_for_each_range().
Since the latter does its own handling of XArray locking, the xas_lock()
and xas_unlock() calls around the original loop are no longer necessary.

The switch to xa_for_each_range() slows down the loop slightly. This is
acceptable since tcmu_blocks_release() is not relevant for performance.

Link: https://lore.kernel.org/r/20220517192913.21405-1-bostroesser@gmail.com
Fixes: bb9b9eb0ae2e ("scsi: target: tcmu: Fix possible data corruption")
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Bodo Stroesser <bostroesser@...il.com>
Signed-off-by: Martin K. Petersen <martin.petersen@...cle.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/target/target_core_user.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
index f26767a55d38..826b55caa17f 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -1660,13 +1660,14 @@ static int tcmu_check_and_free_pending_cmd(struct tcmu_cmd *cmd)
 static u32 tcmu_blocks_release(struct tcmu_dev *udev, unsigned long first,
 				unsigned long last)
 {
-	XA_STATE(xas, &udev->data_pages, first * udev->data_pages_per_blk);
 	struct page *page;
+	unsigned long dpi;
 	u32 pages_freed = 0;
 
-	xas_lock(&xas);
-	xas_for_each(&xas, page, (last + 1) * udev->data_pages_per_blk - 1) {
-		xas_store(&xas, NULL);
+	first = first * udev->data_pages_per_blk;
+	last = (last + 1) * udev->data_pages_per_blk - 1;
+	xa_for_each_range(&udev->data_pages, dpi, page, first, last) {
+		xa_erase(&udev->data_pages, dpi);
 		/*
 		 * While reaching here there may be page faults occurring on
 		 * the to-be-released pages. A race condition may occur if
@@ -1690,7 +1691,6 @@ static u32 tcmu_blocks_release(struct tcmu_dev *udev, unsigned long first,
 		__free_page(page);
 		pages_freed++;
 	}
-	xas_unlock(&xas);
 
 	atomic_sub(pages_freed, &global_page_count);
 
-- 
2.35.1