sysrq,rcu: suppress RCU stall warnings while sysrq runs

sysrq,rcu: suppress RCU stall warnings while sysrq runs

Some sysrq handlers can run for a long time, because they dump a lot of
data onto a serial console.  Having RCU stall warnings pop up in the
middle of them only makes the problem worse.

This patch temporarily disables RCU stall warnings while a sysrq request
is handled.

Signed-off-by: Rik van Riel <[email protected]>
Suggested-by: Paul McKenney <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Cc: Madper Xie <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Richard Weinberger <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>