In the Linux kernel, the following vulnerability has been resolved:

scsi: core: Move scsi_host_busy() out of host lock for waking up EH handler

Inside scsi_eh_wakeup(), scsi_host_busy() is called & checked with host
lock every time for deciding if error handler kthread needs to be waken up.

This can be too heavy in case of recovery, such as:

 - N hardware queues

 - queue depth is M for each hardware queue

 - each scsi_host_busy() iterates over (N * M) tag/requests

If recovery is triggered in case that all requests are in-flight, each
scsi_eh_wakeup() is strictly serialized, when scsi_eh_wakeup() is called
for the last in-flight request, scsi_host_busy() has been run for (N * M -
1) times, and request has been iterated for (N*M - 1) * (N * M) times.

If both N and M are big enough, hard lockup can be triggered on acquiring
host lock, and it is observed on mpi3mr(128 hw queues, queue depth 8169).

Fix the issue by calling scsi_host_busy() outside the host lock. We don't
need the host lock for getting busy count because host the lock never
covers that.

[mkp: Drop unnecessary 'busy' variables pointed out by Bart]

Linux https://git.kernel.org/stable/c/07e3ca0f17f579491b5f54e9ed05173d6c1d6fcb [No types assigned]

Linux https://git.kernel.org/stable/c/4373534a9850627a2695317944898eb1283a2db0 [No types assigned]

Linux https://git.kernel.org/stable/c/65ead8468c21c2676d4d06f50b46beffdea69df1 [No types assigned]

Linux https://git.kernel.org/stable/c/d37c1c81419fdef66ebd0747cf76fb8b7d979059 [No types assigned]

Linux https://git.kernel.org/stable/c/db6338f45971b4285ea368432a84033690eaf53c [No types assigned]

Linux https://git.kernel.org/stable/c/f5944853f7a961fedc1227dc8f60393f8936d37c [No types assigned]