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From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Ani Sinha <ani@arista.com>
Cc: Ani Sinha <ani@anirban.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jslaby@suse.com>,
	linux-kernel@vger.kernel.org, Rik van Riel <riel@redhat.com>,
	Ivan Delalande <colona@arista.com>,
	Francesco Ruggeri <fruggeri@arista.com>
Subject: Re: [PATCH 1/1] Fix 'sleeping function called from invalid context' warning in sysrq generated crash.
Date: Fri, 18 Dec 2015 05:01:25 -0800	[thread overview]
Message-ID: <20151218130125.GO4054@linux.vnet.ibm.com> (raw)
In-Reply-To: <1450401310-29117-1-git-send-email-ani@arista.com>

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 <ani@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 <ani@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 <ani@arista.com>
    Reviewed-by: Rik van Riel <riel@redhat.com>
    Signed-off-by: Paul E. McKenney <paulmck@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;


  reply	other threads:[~2015-12-18 13:06 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-12-18  1:15 Ani Sinha
2015-12-18 13:01 ` Paul E. McKenney [this message]
2015-12-18 15:33   ` Ani Sinha
2015-12-20 14:59   ` Anirban Sinha

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