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From: Ani Sinha <ani@arista.com>
To: Ani Sinha <ani@anirban.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jslaby@suse.com>,
	linux-kernel@vger.kernel.org,
	Paul McKenney <paulmck@linux.vnet.ibm.com>,
	Rik van Riel <riel@redhat.com>,
	Ivan Delalande <colona@arista.com>,
	Francesco Ruggeri <fruggeri@arista.com>
Cc: Ani Sinha <ani@arista.com>
Subject: [PATCH 1/1] Fix 'sleeping function called from invalid context'  warning in sysrq generated crash.
Date: Thu, 17 Dec 2015 17:15:10 -0800	[thread overview]
Message-ID: <1450401310-29117-1-git-send-email-ani@arista.com> (raw)

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


             reply	other threads:[~2015-12-18  1:15 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-12-18  1:15 Ani Sinha [this message]
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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