[PATCH 3/7] cxlflash: Acquire semaphore before invoking ioctl services

[Matthew R. Ochs]

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 <ukrishn at linux.vnet.ibm.com>

Acked-by: Matthew R. Ochs <mrochs at linux.vnet.ibm.com>