[PATCH] ceph: fix variable dereferenced before check in ceph_umount_begin()

[Viacheslav Dubeyko <slava@xxxxxxxxxxx>]

From: Viacheslav Dubeyko <Slava.Dubeyko@xxxxxxx>

smatch warnings:
fs/ceph/super.c:1042 ceph_umount_begin() warn: variable dereferenced before check 'fsc' (see line 1041)

vim +/fsc +1042 fs/ceph/super.c

void ceph_umount_begin(struct super_block *sb)
{
	struct ceph_fs_client *fsc = ceph_sb_to_fs_client(sb);

	doutc(fsc->client, "starting forced umount\n");
              ^^^^^^^^^^^
Dereferenced

	if (!fsc)
            ^^^^
Checked too late.

		return;
	fsc->mount_state = CEPH_MOUNT_SHUTDOWN;
	__ceph_umount_begin(fsc);
}

This patch moves pointer check before the first
dereference of the pointer.

Reported-by: kernel test robot <lkp@xxxxxxxxx>
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Closes: https://urldefense.proofpoint.com/v2/url?u=https-3A__lore.kernel.org_r_202503280852.YDB3pxUY-2Dlkp-40intel.com_&d=DwIBAg&c=BSDicqBQBDjDI9RkVyTcHQ&r=q5bIm4AXMzc8NJu1_RGmnQ2fMWKq4Y4RAkElvUgSs00&m=Ud7uNdqBY_Z7LJ_oI4fwdhvxOYt_5Q58tpkMQgDWhV3199_TCnINFU28Esc0BaAH&s=QOKWZ9HKLyd6XCxW-AUoKiFFg9roId6LOM01202zAk0&e=
Signed-off-by: Viacheslav Dubeyko <Slava.Dubeyko@xxxxxxx>
---
 fs/ceph/super.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/ceph/super.c b/fs/ceph/super.c
index f3951253e393..6cbc33c56e0e 100644
--- a/fs/ceph/super.c
+++ b/fs/ceph/super.c
@@ -1032,9 +1032,11 @@ void ceph_umount_begin(struct super_block *sb)
 {
 	struct ceph_fs_client *fsc = ceph_sb_to_fs_client(sb);
 
-	doutc(fsc->client, "starting forced umount\n");
 	if (!fsc)
 		return;
+
+	doutc(fsc->client, "starting forced umount\n");
+
 	fsc->mount_state = CEPH_MOUNT_SHUTDOWN;
 	__ceph_umount_begin(fsc);
 }
-- 
2.48.0