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* [PATCH 1/1] Fix 'sleeping function called from invalid context'  warning in sysrq generated crash.
@ 2015-12-18  1:15 Ani Sinha
  2015-12-18 13:01 ` Paul E. McKenney
  0 siblings, 1 reply; 4+ messages in thread
From: Ani Sinha @ 2015-12-18  1:15 UTC (permalink / raw)
  To: Ani Sinha, Greg Kroah-Hartman, Jiri Slaby, linux-kernel,
	Paul McKenney, Rik van Riel, Ivan Delalande, Francesco Ruggeri
  Cc: Ani Sinha

Commit 984d74a72076a1 ("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: 984d74a72076a1 ("sysrq: rcu-ify __handle_sysrq")

Signed-off-by: Ani Sinha <ani@arista.com>
---
 drivers/tty/sysrq.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 5381a72..08987ad 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -133,6 +133,12 @@ static void sysrq_handle_crash(int key)
 {
 	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 */
 	wmb();
 	*killer = 1;
-- 
1.8.1.4


^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2015-12-20 14:59 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2015-12-18  1:15 [PATCH 1/1] Fix 'sleeping function called from invalid context' warning in sysrq generated crash Ani Sinha
2015-12-18 13:01 ` Paul E. McKenney
2015-12-18 15:33   ` Ani Sinha
2015-12-20 14:59   ` Anirban Sinha

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