Commit 984cf355 authored Dec 17, 2015 by Ani Sinha Committed by Paul E. McKenney Dec 29, 2015

sysrq: Fix warning in sysrq generated crash.



Commit 984d74a7 ("sysrq: rcu-ify __handle_sysrq") replaced
spin_lock_irqsave() calls with rcu_read_lock() calls in sysrq. Since
rcu_read_lock() does not disable preemption, faulthandler_disabled() in
__do_page_fault() in x86/fault.c returns false. When the code later calls
might_sleep() in the pagefault handler, we get the following warning:

BUG: sleeping function called from invalid context at ../arch/x86/mm/fault.c:1187
in_atomic(): 0, irqs_disabled(): 0, pid: 4706, name: bash
Preemption disabled at:[<ffffffff81484339>] printk+0x48/0x4a

To fix this, we release the RCU read lock before we crash.

Tested this patch on linux 3.18 by booting off one of our boards.

Fixes: 984d74a7 ("sysrq: rcu-ify __handle_sysrq")

Signed-off-by: Ani Sinha <ani@arista.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

parent 648c630c

drivers/tty/sysrq.c

+6 −0

Original line number	Original line	Diff line number	Diff line
	@@ -133,6 +133,12 @@ static void sysrq_handle_crash(int key)
	{		{
	char *killer = NULL;		char *killer = NULL;

			/* we need to release the RCU read lock here,
			* otherwise we get an annoying
			* 'BUG: sleeping function called from invalid context'
			* complaint from the kernel before the panic.
			*/
			rcu_read_unlock();
	panic_on_oops = 1; /* force panic */		panic_on_oops = 1; /* force panic */
	wmb();		wmb();
	*killer = 1;		*killer = 1;