[PATCH RT 07/10] net/core/cpuhotplug: Drain input_pkt_queue lockless

From: Steven Rostedt
Date: Fri Feb 26 2016 - 17:22:07 EST


3.12.54-rt73-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Grygorii Strashko <grygorii.strashko@xxxxxx>

I can constantly see below error report with 4.1 RT-kernel on TI ARM dra7-evm
if I'm trying to unplug cpu1:

[ 57.737589] CPU1: shutdown
[ 57.767537] BUG: spinlock bad magic on CPU#0, sh/137
[ 57.767546] lock: 0xee994730, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0
[ 57.767552] CPU: 0 PID: 137 Comm: sh Not tainted 4.1.10-rt8-01700-g2c38702-dirty #55
[ 57.767555] Hardware name: Generic DRA74X (Flattened Device Tree)
[ 57.767568] [<c001acd0>] (unwind_backtrace) from [<c001534c>] (show_stack+0x20/0x24)
[ 57.767579] [<c001534c>] (show_stack) from [<c075560c>] (dump_stack+0x84/0xa0)
[ 57.767593] [<c075560c>] (dump_stack) from [<c00aca48>] (spin_dump+0x84/0xac)
[ 57.767603] [<c00aca48>] (spin_dump) from [<c00acaa4>] (spin_bug+0x34/0x38)
[ 57.767614] [<c00acaa4>] (spin_bug) from [<c00acc10>] (do_raw_spin_lock+0x168/0x1c0)
[ 57.767624] [<c00acc10>] (do_raw_spin_lock) from [<c075b4cc>] (_raw_spin_lock+0x4c/0x54)
[ 57.767631] [<c075b4cc>] (_raw_spin_lock) from [<c07599fc>] (rt_spin_lock_slowlock+0x5c/0x374)
[ 57.767638] [<c07599fc>] (rt_spin_lock_slowlock) from [<c075bcf4>] (rt_spin_lock+0x38/0x70)
[ 57.767649] [<c075bcf4>] (rt_spin_lock) from [<c06333c0>] (skb_dequeue+0x28/0x7c)
[ 57.767662] [<c06333c0>] (skb_dequeue) from [<c06476ec>] (dev_cpu_callback+0x1b8/0x240)
[ 57.767673] [<c06476ec>] (dev_cpu_callback) from [<c007566c>] (notifier_call_chain+0x3c/0xb4)

The reason is that skb_dequeue is taking skb->lock, but RT changed the
core code to use a raw spinlock. The non-raw lock is not initialized
on purpose to catch exactly this kind of problem.

Fixes: 91df05da13a6 'net: Use skbufhead with raw lock'
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: stable-rt@xxxxxxxxxxxxxxx
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
net/core/dev.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index ea6092bd8219..cfec8a542d35 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6481,7 +6481,7 @@ static int dev_cpu_callback(struct notifier_block *nfb,
netif_rx(skb);
input_queue_head_incr(oldsd);
}
- while ((skb = skb_dequeue(&oldsd->input_pkt_queue))) {
+ while ((skb = __skb_dequeue(&oldsd->input_pkt_queue))) {
netif_rx(skb);
input_queue_head_incr(oldsd);
}
--
2.7.0