This is a note to let you know that I've just added the patch titled
KVM: async_pf: make rcu irq exit if not triggered from idle task
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
kvm-async_pf-make-rcu-irq-exit-if-not-triggered-from-idle-task.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 337c017ccdf2653d0040099433fc1a2b1beb5926 Mon Sep 17 00:00:00 2001
From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
Date: Tue, 1 Aug 2017 05:20:03 -0700
Subject: KVM: async_pf: make rcu irq exit if not triggered from idle task
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From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
commit 337c017ccdf2653d0040099433fc1a2b1beb5926 upstream.
WARNING: CPU: 5 PID: 1242 at kernel/rcu/tree_plugin.h:323 rcu_note_context_switch+0x207/0x6b0
CPU: 5 PID: 1242 Comm: unity-settings- Not tainted 4.13.0-rc2+ #1
RIP: 0010:rcu_note_context_switch+0x207/0x6b0
Call Trace:
__schedule+0xda/0xba0
? kvm_async_pf_task_wait+0x1b2/0x270
schedule+0x40/0x90
kvm_async_pf_task_wait+0x1cc/0x270
? prepare_to_swait+0x22/0x70
do_async_page_fault+0x77/0xb0
? do_async_page_fault+0x77/0xb0
async_page_fault+0x28/0x30
RIP: 0010:__d_lookup_rcu+0x90/0x1e0
I encounter this when trying to stress the async page fault in L1 guest w/
L2 guests running.
Commit 9b132fbe5419 (Add rcu user eqs exception hooks for async page
fault) adds rcu_irq_enter/exit() to kvm_async_pf_task_wait() to exit cpu
idle eqs when needed, to protect the code that needs use rcu. However,
we need to call the pair even if the function calls schedule(), as seen
from the above backtrace.
This patch fixes it by informing the RCU subsystem exit/enter the irq
towards/away from idle for both n.halted and !n.halted.
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Radim Krčmář <rkrcmar@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/kvm.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -151,6 +151,8 @@ void kvm_async_pf_task_wait(u32 token)
if (hlist_unhashed(&n.link))
break;
+ rcu_irq_exit();
+
if (!n.halted) {
local_irq_enable();
schedule();
@@ -159,11 +161,11 @@ void kvm_async_pf_task_wait(u32 token)
/*
* We cannot reschedule. So halt.
*/
- rcu_irq_exit();
native_safe_halt();
local_irq_disable();
- rcu_irq_enter();
}
+
+ rcu_irq_enter();
}
if (!n.halted)
finish_wait(&n.wq, &wait);
Patches currently in stable-queue which might be from wanpeng.li@xxxxxxxxxxx are
queue-4.4/kvm-async_pf-make-rcu-irq-exit-if-not-triggered-from-idle-task.patch