Messages in this thread | | | Subject | Re: new warning on sysrq kernel crash trigger | From | Rik van Riel <> | Date | Wed, 16 Dec 2015 11:22:46 -0500 |
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On 12/14/2015 07:14 PM, Anirban Sinha wrote: > > > On Mon, 14 Dec 2015, Rik van Riel wrote: > >> On 12/14/2015 11:24 AM, Ani Sinha wrote: >>> Rik, any comments? >> >> Another good option is to simply ignore this warning, or drop the >> rcu_read_lock before doing the alt-syrsq-c action. >> >> After all, alt-sysrq-c is "crash the system, take a crash dump", >> which is not an action the system ever returns from. >> > > Yea I thought about this idea previously but then discarded it > thinking it would be too hacky. Here's the cooked up patch. I hope > this can be approved for mainline soon (I'm on vacation and working > just on this issue remotely) : > > From 105ff3ffce380650b3d58b3594a9be47bd604b28 Mon Sep 17 00:00:00 > 2001 From: Ani Sinha <ani@arista.com> Date: Mon, 14 Dec 2015 > 14:55:08 -0800 Subject: [PATCH 1/1] Fix 'sleeping function called > from invalid context' 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 <ani@arista.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
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