On Thu, Dec 17, 2015 at 05:15:10PM -0800, Ani Sinha wrote:
> 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 <a...@arista.com>
I queued this with Rik's Signed-off-by, and fixed some checkpatch.pl
errors. Please run scripts/checkpatch.pl on your patches in the future.
Please see below for the result.
Rik, did you test this as well? If so, may I also have your Tested-by?
Thanx, Paul
------------------------------------------------------------------------
commit c95a158356397844a5a6deb0bd58758084f891df
Author: Ani Sinha <a...@arista.com>
Date: Thu Dec 17 17:15:10 2015 -0800
sysrq: Fix warning in sysrq generated crash.
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 <a...@arista.com>
Reviewed-by: Rik van Riel <r...@redhat.com>
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 5381a728d23e..e5139402e7f8 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;
--
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