| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.4 44/87] sysrq: Fix warning in sysrq generated crash. | Date | Mon, 15 Jan 2018 13:34:43 +0100 |
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4.4-stable review patch. If anyone has any objections, please let me know.
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From: Ani Sinha <ani@arista.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@arista.com> Reviewed-by: Rik van Riel <riel@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- drivers/tty/sysrq.c | 6 ++++++ 1 file changed, 6 insertions(+)
--- 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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