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

Greg Kroah-Hartman
2022-06-07T20:46:35Z

From: Bodo Stroesser <bostroesser@gmail.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@oracle.com>
Signed-off-by: Bodo Stroesser <bostroesser@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.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