* [PATCH] net: mac80211: Disable preeemption when updating stat counters
@ 2019-09-27 15:41 Aaron Hill
2019-10-01 10:00 ` Johannes Berg
0 siblings, 1 reply; 2+ messages in thread
From: Aaron Hill @ 2019-09-27 15:41 UTC (permalink / raw)
To: linux-wireless; +Cc: Johannes Berg, David S. Miller, netdev, linux-kernel
The mac80211 subsystem maintains per-cpu stat counters for receive and
transmit operations. Previously, preemption was not disabled when
updating these counters. This creates a race condition where two cpus
could attempt to update the same counters using non-atomic operations.
This was causing a
'BUG: using smp_processor_id() in preemptible [00000000] code'
message to be printed, along with a stacktrace. This was reported
in a few different places:
* https://www.spinics.net/lists/linux-wireless/msg189992.html
* https://bugzilla.kernel.org/show_bug.cgi?id=204127
This patch adds calls to preempt_disable() and preempt_enable()
surrounding the updating of the stat counters.
Signed-off-by: Aaron Hill <aa1ronham@gmail.com>
---
net/mac80211/rx.c | 7 ++++++-
net/mac80211/tx.c | 7 ++++++-
2 files changed, 12 insertions(+), 2 deletions(-)
diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index 768d14c9a716..5ef0667151bf 100644
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -34,12 +34,17 @@
static inline void ieee80211_rx_stats(struct net_device *dev, u32 len)
{
- struct pcpu_sw_netstats *tstats = this_cpu_ptr(dev->tstats);
+ struct pcpu_sw_netstats *tstats;
+
+ // Disable preemption while updating per-cpu stats counters
+ preempt_disable();
+ tstats = this_cpu_ptr(dev->tstats);
u64_stats_update_begin(&tstats->syncp);
tstats->rx_packets++;
tstats->rx_bytes += len;
u64_stats_update_end(&tstats->syncp);
+ preempt_enable();
}
static u8 *ieee80211_get_bssid(struct ieee80211_hdr *hdr, size_t len,
diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 1fa422782905..4cad3d741b6b 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -40,12 +40,17 @@
static inline void ieee80211_tx_stats(struct net_device *dev, u32 len)
{
- struct pcpu_sw_netstats *tstats = this_cpu_ptr(dev->tstats);
+ struct pcpu_sw_netstats *tstats;
+
+ // Disable preemption while updating per-cpu stats counters
+ preempt_disable();
+ tstats = this_cpu_ptr(dev->tstats);
u64_stats_update_begin(&tstats->syncp);
tstats->tx_packets++;
tstats->tx_bytes += len;
u64_stats_update_end(&tstats->syncp);
+ preempt_enable();
}
static __le16 ieee80211_duration(struct ieee80211_tx_data *tx,
--
2.23.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] net: mac80211: Disable preeemption when updating stat counters
2019-09-27 15:41 [PATCH] net: mac80211: Disable preeemption when updating stat counters Aaron Hill
@ 2019-10-01 10:00 ` Johannes Berg
0 siblings, 0 replies; 2+ messages in thread
From: Johannes Berg @ 2019-10-01 10:00 UTC (permalink / raw)
To: Aaron Hill, linux-wireless
Cc: David S. Miller, netdev, linux-kernel, Jiri Kosina,
Toke Høiland-Jørgensen
On Fri, 2019-09-27 at 11:41 -0400, Aaron Hill wrote:
> The mac80211 subsystem maintains per-cpu stat counters for receive and
> transmit operations. Previously, preemption was not disabled when
> updating these counters. This creates a race condition where two cpus
> could attempt to update the same counters using non-atomic operations.
>
> This was causing a
> 'BUG: using smp_processor_id() in preemptible [00000000] code'
> message to be printed, along with a stacktrace. This was reported
> in a few different places:
>
> * https://www.spinics.net/lists/linux-wireless/msg189992.html
> * https://bugzilla.kernel.org/show_bug.cgi?id=204127
>
> This patch adds calls to preempt_disable() and preempt_enable()
> surrounding the updating of the stat counters.
That seems like basically the same as what Jiri reported, but now I'm
even more confused...
Ah. CONFIG_PREEMPT_RCU...
But if we keep BHs disabled, it should still be OK, so what I suggested
to Jiri will also address this I think?
diff --git a/net/mac80211/util.c b/net/mac80211/util.c
index 051a02ddcb85..ad1e88958da2 100644
--- a/net/mac80211/util.c
+++ b/net/mac80211/util.c
@@ -273,9 +273,9 @@ static void __ieee80211_wake_txqs(struct ieee80211_sub_if_data *sdata, int ac)
&txqi->flags))
continue;
- spin_unlock_bh(&fq->lock);
+ spin_unlock(&fq->lock);
drv_wake_tx_queue(local, txqi);
- spin_lock_bh(&fq->lock);
+ spin_lock(&fq->lock);
}
}
johannes
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2019-10-01 10:00 ` Johannes Berg
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