From: Ani Sinha ani@arista.com
This patch has been added to the 4.1 stable tree. If you have any objections, please let us know.
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[ Upstream commit 984cf355aeaa8f2eda3861b50d0e8d3e3f77e83b ]
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 Reviewed-by: Rik van Riel riel@redhat.com Signed-off-by: Paul E. McKenney paulmck@linux.vnet.ibm.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- drivers/tty/sysrq.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c index 529cc86283e7..9c27ee008dff 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;