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Subject[RFC PATCH net-next] sfc: replace in_interrupt() usage
Date
efx_ef10_try_update_nic_stats_vf() used in_interrupt() to figure out
whether it is safe to sleep (for MCDI) or not.
The only caller from which it was not is efx_net_stats(), which can be
invoked under dev_base_lock from net-sysfs::netstat_show().
So add a new update_stats_atomic() method to struct efx_nic_type, and
call it from efx_net_stats(), removing the need for
efx_ef10_try_update_nic_stats_vf() to behave differently for this case
(which it wasn't doing correctly anyway).
For all nic_types other than EF10 VF, this method is NULL and so we
call the regular update_stats() methods, which are happy with being
called from atomic contexts.

Fixes: f00bf2305cab ("sfc: don't update stats on VF when called in atomic context")
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Edward Cree <ecree@solarflare.com>
---
Only compile-tested so far, because I'm waiting for my kernel to
finish rebuilding with CONFIG_DEBUG_ATOMIC_SLEEP which I'm hoping
is the right thing to detect the bug in the existing code.
I also wasn't quite sure how to give credit to the thorough analysis
in the commit message of Sebastian's patch. I don't think we have
a Whatever-by: tag to cover that, do we?
And this doesn't include your GFP_KERNEL change, which should
probably go in separately if you take this.

drivers/net/ethernet/sfc/ef10.c | 22 +++++++++++++---------
drivers/net/ethernet/sfc/efx_common.c | 2 +-
drivers/net/ethernet/sfc/net_driver.h | 5 +++++
drivers/net/ethernet/sfc/nic_common.h | 7 +++++++
4 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/drivers/net/ethernet/sfc/ef10.c b/drivers/net/ethernet/sfc/ef10.c
index c9df2e96ebe4..b702ba5986dc 100644
--- a/drivers/net/ethernet/sfc/ef10.c
+++ b/drivers/net/ethernet/sfc/ef10.c
@@ -1871,15 +1871,6 @@ static int efx_ef10_try_update_nic_stats_vf(struct efx_nic *efx)

spin_unlock_bh(&efx->stats_lock);

- if (in_interrupt()) {
- /* If in atomic context, cannot update stats. Just update the
- * software stats and return so the caller can continue.
- */
- spin_lock_bh(&efx->stats_lock);
- efx_update_sw_stats(efx, stats);
- return 0;
- }
-
efx_ef10_get_stat_mask(efx, mask);

rc = efx_nic_alloc_buffer(efx, &stats_buf, dma_len, GFP_ATOMIC);
@@ -1938,6 +1929,18 @@ static size_t efx_ef10_update_stats_vf(struct efx_nic *efx, u64 *full_stats,
return efx_ef10_update_stats_common(efx, full_stats, core_stats);
}

+static size_t efx_ef10_update_stats_atomic_vf(struct efx_nic *efx, u64 *full_stats,
+ struct rtnl_link_stats64 *core_stats)
+{
+ struct efx_ef10_nic_data *nic_data = efx->nic_data;
+
+ /* In atomic context, cannot update HW stats. Just update the
+ * software stats and return so the caller can continue.
+ */
+ efx_update_sw_stats(efx, nic_data->stats);
+ return efx_ef10_update_stats_common(efx, full_stats, core_stats);
+}
+
static void efx_ef10_push_irq_moderation(struct efx_channel *channel)
{
struct efx_nic *efx = channel->efx;
@@ -3998,6 +4001,7 @@ const struct efx_nic_type efx_hunt_a0_vf_nic_type = {
.finish_flr = efx_port_dummy_op_void,
.describe_stats = efx_ef10_describe_stats,
.update_stats = efx_ef10_update_stats_vf,
+ .update_stats_atomic = efx_ef10_update_stats_atomic_vf,
.start_stats = efx_port_dummy_op_void,
.pull_stats = efx_port_dummy_op_void,
.stop_stats = efx_port_dummy_op_void,
diff --git a/drivers/net/ethernet/sfc/efx_common.c b/drivers/net/ethernet/sfc/efx_common.c
index c256db241570..72a3f0e09f52 100644
--- a/drivers/net/ethernet/sfc/efx_common.c
+++ b/drivers/net/ethernet/sfc/efx_common.c
@@ -602,7 +602,7 @@ void efx_net_stats(struct net_device *net_dev, struct rtnl_link_stats64 *stats)
struct efx_nic *efx = netdev_priv(net_dev);

spin_lock_bh(&efx->stats_lock);
- efx->type->update_stats(efx, NULL, stats);
+ efx_nic_update_stats_atomic(efx, NULL, stats);
spin_unlock_bh(&efx->stats_lock);
}

diff --git a/drivers/net/ethernet/sfc/net_driver.h b/drivers/net/ethernet/sfc/net_driver.h
index 47aa753e64bd..9f7dfdf708cf 100644
--- a/drivers/net/ethernet/sfc/net_driver.h
+++ b/drivers/net/ethernet/sfc/net_driver.h
@@ -1172,6 +1172,9 @@ struct efx_udp_tunnel {
* @describe_stats: Describe statistics for ethtool
* @update_stats: Update statistics not provided by event handling.
* Either argument may be %NULL.
+ * @update_stats_atomic: Update statistics while in atomic context, if that
+ * is more limiting than @update_stats. Otherwise, leave %NULL and
+ * driver core will call @update_stats.
* @start_stats: Start the regular fetching of statistics
* @pull_stats: Pull stats from the NIC and wait until they arrive.
* @stop_stats: Stop the regular fetching of statistics
@@ -1316,6 +1319,8 @@ struct efx_nic_type {
size_t (*describe_stats)(struct efx_nic *efx, u8 *names);
size_t (*update_stats)(struct efx_nic *efx, u64 *full_stats,
struct rtnl_link_stats64 *core_stats);
+ size_t (*update_stats_atomic)(struct efx_nic *efx, u64 *full_stats,
+ struct rtnl_link_stats64 *core_stats);
void (*start_stats)(struct efx_nic *efx);
void (*pull_stats)(struct efx_nic *efx);
void (*stop_stats)(struct efx_nic *efx);
diff --git a/drivers/net/ethernet/sfc/nic_common.h b/drivers/net/ethernet/sfc/nic_common.h
index 82271f0b8627..b9cafe9cd568 100644
--- a/drivers/net/ethernet/sfc/nic_common.h
+++ b/drivers/net/ethernet/sfc/nic_common.h
@@ -244,6 +244,13 @@ void efx_nic_update_stats(const struct efx_hw_stat_desc *desc, size_t count,
const unsigned long *mask, u64 *stats,
const void *dma_buf, bool accumulate);
void efx_nic_fix_nodesc_drop_stat(struct efx_nic *efx, u64 *stat);
+static inline size_t efx_nic_update_stats_atomic(struct efx_nic *efx, u64 *full_stats,
+ struct rtnl_link_stats64 *core_stats)
+{
+ if (efx->type->update_stats_atomic)
+ return efx->type->update_stats_atomic(efx, full_stats, core_stats);
+ return efx->type->update_stats(efx, full_stats, core_stats);
+}

#define EFX_MAX_FLUSH_TIME 5000

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