On Fri, May 11, 2018 at 02:05:22PM -0500, Uma Krishnan wrote:

When a superpipe process that makes use of virtual LUNs is terminated or
killed abruptly, there is a possibility that the cxlflash driver could
hang and deprive other operations on the adapter.

The release fop registered to be invoked on a context close, detaches
every LUN associated with the context. The underlying service to detach
the LUN assumes it has been called with the read semaphore held, and
releases the semaphore before any operation that could be time consuming.

When invoked without holding the read semaphore, an opportunity is created
for the semaphore's count to become negative when it is temporarily
released during one of these potential lengthy operations. This negative
count results in subsequent acquisition attempts taking forever, leading
to the hang.

To support the current design point of holding the semaphore on the
ioctl() paths, the release fop should acquire it before invoking any
ioctl services.

Signed-off-by: Uma Krishnan <redacted>

Acked-by: Matthew R. Ochs <redacted>