On Thu, 2017-08-03 at 21:33 -0700, Florian Fainelli wrote:
> During testing with a background iperf pushing 1Gbit/sec worth of
> traffic and having both ifconfig and ethtool collect statistics, we
> could see quite frequent deadlocks. Convert the often accessed DSA slave
> network devices statistics to per-cpu 64-bit statistics to remove these
> deadlocks and provide fast efficient statistics updates.
>
This seems to be a bug fix, it would be nice to get a proper tag like :
Fixes: f613ed665bb3 ("net: dsa: Add support for 64-bit statistics")
Problem here is that if multiple cpus can call dsa_switch_rcv() at the
same time, then u64_stats_update_begin() contract is not respected.
include/linux/u64_stats_sync.h states :
* Usage :
*
* Stats producer (writer) should use following template granted it already got
* an exclusive access to counters (a lock is already taken, or per cpu
* data is used [in a non preemptable context])
*
* spin_lock_bh(...) or other synchronization to get exclusive access
* ...
* u64_stats_update_begin(&stats->syncp);
