net: dsa: xrs700x: Use irqsave variant for u64 stats update
authorSebastian Andrzej Siewior <bigeasy@linutronix.de>
Thu, 25 Aug 2022 11:36:44 +0000 (13:36 +0200)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Thu, 8 Sep 2022 10:28:02 +0000 (12:28 +0200)
commitd6ec2f711c945ee969be5709aa23e40ae4c57368
treee61842214b21bb2a78d926ac04db79be30fdda32
parentca54b2bfaab385778e55a9fd33f6c31e7f743b48
net: dsa: xrs700x: Use irqsave variant for u64 stats update

[ Upstream commit 3f8ae9fe0409698799e173f698b714f34570b64b ]

xrs700x_read_port_counters() updates the stats from a worker using the
u64_stats_update_begin() version. This is okay on 32-UP since on the
reader side preemption is disabled.
On 32bit-SMP the writer can be preempted by the reader at which point
the reader will spin on the seqcount until writer continues and
completes the update.

Assigning the mib_mutex mutex to the underlying seqcount would ensure
proper synchronisation. The API for that on the u64_stats_init() side
isn't available. Since it is the only user, just use disable interrupts
during the update.

Use u64_stats_update_begin_irqsave() on the writer side to ensure an
uninterrupted update.

Fixes: ee00b24f32eb8 ("net: dsa: add Arrow SpeedChips XRS700x driver")
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: George McCollister <george.mccollister@gmail.com>
Cc: Vivien Didelot <vivien.didelot@gmail.com>
Cc: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: George McCollister <george.mccollister@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
drivers/net/dsa/xrs700x/xrs700x.c