md/raid5: release batch_last before waiting for another stripe_head

When raid5_get_active_stripe is called with a ctx containing a stripe_head in
its batch_last pointer, it can cause a deadlock if the task sleeps waiting on
another stripe_head to become available. The stripe_head held by batch_last
can be blocking the advancement of other stripe_heads, leading to no
stripe_heads being released so raid5_get_active_stripe waits forever.

Like with the quiesce state handling earlier in the function, batch_last
needs to be released by raid5_get_active_stripe before it waits for another
stripe_head.

Fixes: 3312e6c887fe ("md/raid5: Keep a reference to last stripe_head for batch")
Cc: [email protected] # v6.0+
Signed-off-by: David Jeffery <[email protected]>
Reviewed-by: Logan Gunthorpe <[email protected]>
Signed-off-by: Song Liu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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