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Subject[PATCH] net: mac80211: Disable preeemption when updating stat counters
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
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