srcu: Permit Tiny SRCU srcu_read_unlock() with interrupts disabled

srcu: Permit Tiny SRCU srcu_read_unlock() with interrupts disabled

The current Tiny SRCU implementation of srcu_read_unlock() awakens
the grace-period processing when exiting the outermost SRCU read-side
critical section.  However, not all Linux-kernel configurations and
contexts permit swake_up_one() to be invoked while interrupts are
disabled, and this can result in indefinitely extended SRCU grace periods.
This commit therefore only invokes swake_up_one() when interrupts are
enabled, and introduces polling to the grace-period workqueue handler.

Reported-by: kernel test robot <oliver.sang@intel.com>
Reported-by: Zqiang <qiang.zhang@linux.dev>
Closes: https://lore.kernel.org/oe-lkp/202508261642.b15eefbb-lkp@intel.com
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>