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Message-Id: <1454030348-17736-164-git-send-email-kamal@canonical.com>
Date: Thu, 28 Jan 2016 17:18:21 -0800
From: Kamal Mostafa <kamal@...onical.com>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
kernel-team@...ts.ubuntu.com
Cc: Ani Sinha <ani@...sta.com>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.19.y-ckt 163/210] sysrq: Fix warning in sysrq generated crash.
3.19.8-ckt14 -stable review patch. If anyone has any objections, please let me know.
---8<------------------------------------------------------------
From: Ani Sinha <ani@...sta.com>
commit 984cf355aeaa8f2eda3861b50d0e8d3e3f77e83b upstream.
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@...sta.com>
Reviewed-by: Rik van Riel <riel@...hat.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
drivers/tty/sysrq.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 647d3df..4ea543b 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;
--
1.9.1
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