linux-kernel - [PATCH] dm: remove unnecessary check when using dm_get

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Message-Id: <20221216042353.3132139-1-houtao@huaweicloud.com>
Date:   Fri, 16 Dec 2022 12:23:53 +0800
From:   Hou Tao <houtao@...weicloud.com>
To:     dm-devel@...hat.com
Cc:     Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...nel.org>,
        linux-kernel@...r.kernel.org, houtao1@...wei.com
Subject: [PATCH] dm: remove unnecessary check when using dm_get_mdptr()

From: Hou Tao <houtao1@...wei.com>

__hash_remove() removes hash_cell with _hash_lock locked, so acquiring
_hash_lock can guarantee no-NULL hc returned from dm_get_mdptr() must
have not been removed and hc->md must still be md.

__hash_remove() also acquires dm_hash_cells_mutex before setting mdptr
as NULL, so in dm_copy_name_and_uuid() after acquiring
dm_hash_cells_mutex and ensuring returned hc is not NULL, the returned
hc must still be alive and hc->md must still be md.

So removing these unnecessary hc->md != md checks when using
dm_get_mdptr() with _hash_lock or dm_hash_cells_mutex acquired.

Signed-off-by: Hou Tao <houtao1@...wei.com>
---
 drivers/md/dm-ioctl.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 3bfc1583c20a..2a86524661d1 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -772,7 +772,7 @@ static struct dm_table *dm_get_inactive_table(struct mapped_device *md, int *src
 
 	down_read(&_hash_lock);
 	hc = dm_get_mdptr(md);
-	if (!hc || hc->md != md) {
+	if (!hc) {
 		DMERR("device has been removed from the dev hash table.");
 		goto out;
 	}
@@ -1476,7 +1476,7 @@ static int table_load(struct file *filp, struct dm_ioctl *param, size_t param_si
 	/* stage inactive table */
 	down_write(&_hash_lock);
 	hc = dm_get_mdptr(md);
-	if (!hc || hc->md != md) {
+	if (!hc) {
 		DMERR("device has been removed from the dev hash table.");
 		up_write(&_hash_lock);
 		r = -ENXIO;
@@ -2128,7 +2128,7 @@ int dm_copy_name_and_uuid(struct mapped_device *md, char *name, char *uuid)
 
 	mutex_lock(&dm_hash_cells_mutex);
 	hc = dm_get_mdptr(md);
-	if (!hc || hc->md != md) {
+	if (!hc) {
 		r = -ENXIO;
 		goto out;
 	}
-- 
2.29.2