s390/zcore: fix race when reading from hardware system area

stable inclusion
from stable-v5.10.137
commit 9c2ad32ed91665ca09ddb25d8bda8bbf9963b6f0
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I60PLB

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9c2ad32ed91665ca09ddb25d8bda8bbf9963b6f0



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[ Upstream commit 9ffed254 ]

Memory buffer used for reading out data from hardware system
area is not protected against concurrent access.

Reported-by: Matthew Wilcox <willy@infradead.org>
Fixes: 411ed322 ("[S390] zfcpdump support.")
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Tested-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Link: https://lore.kernel.org/r/e68137f0f9a0d2558f37becc20af18e2939934f6.1658206891.git.agordeev@linux.ibm.com


Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: Wei Li <liwei391@huawei.com>