diff mbox series

[net-next,09/24] dev: Use the RPS lock for softnet_data::input_pkt_queue on PREEMPT_RT.

Message ID 20231215171020.687342-10-bigeasy@linutronix.de (mailing list archive)
State Changes Requested
Delegated to: Netdev Maintainers
Headers show
Series locking: Introduce nested-BH locking. | expand

Checks

Context Check Description
netdev/series_format fail Series longer than 15 patches (and no cover letter)
netdev/tree_selection success Clearly marked for net-next, async
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 1123 this patch: 1123
netdev/cc_maintainers success CCed 4 of 4 maintainers
netdev/build_clang success Errors and warnings before: 1143 this patch: 1143
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 1150 this patch: 1150
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 42 lines checked
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0

Commit Message

Sebastian Andrzej Siewior Dec. 15, 2023, 5:07 p.m. UTC 
There is no additional locking in rps_lock_*() on PREEMPT_RT in the
!CONFIG_RPS case. The reasoning is that local_bh_disable() provides the
required synchronization (everywhere).
All interrupts are threaded and so the required CPU local
synchronization is provided by the per-CPU lock in local_bh_disable()
which is always performed for the forced-threaded interrupts.
Needless to say that the softirq users (NAPI) have BH disabled while
being invoked as a softirq callback.

Without locking in local_bh_disable() on PREEMPT_RT the
softnet_data::input_pkt_queue data structure requires explicit locking
in the !CONFIG_RPS case.

Disabling interrupts for CPU-local locking is undesired because it will
impose restrictions within the locked sections like not allowing to free
a skb.

Utilise the locking which is present in the CONFIG_RPS case for
serialisation on PREEMPT_RT even without CONFIG_RPS enabled.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 net/core/dev.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)
diff mbox series

Patch

diff --git a/net/core/dev.c b/net/core/dev.c
index c879246be48d8..09232080843ee 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -220,34 +220,34 @@  static inline struct hlist_head *dev_index_hash(struct net *net, int ifindex)
 static inline void rps_lock_irqsave(struct softnet_data *sd,
 				    unsigned long *flags)
 {
-	if (IS_ENABLED(CONFIG_RPS))
+	if (IS_ENABLED(CONFIG_RPS) || IS_ENABLED(CONFIG_PREEMPT_RT))
 		spin_lock_irqsave(&sd->input_pkt_queue.lock, *flags);
-	else if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+	else
 		local_irq_save(*flags);
 }
 
 static inline void rps_lock_irq_disable(struct softnet_data *sd)
 {
-	if (IS_ENABLED(CONFIG_RPS))
+	if (IS_ENABLED(CONFIG_RPS) || IS_ENABLED(CONFIG_PREEMPT_RT))
 		spin_lock_irq(&sd->input_pkt_queue.lock);
-	else if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+	else
 		local_irq_disable();
 }
 
 static inline void rps_unlock_irq_restore(struct softnet_data *sd,
 					  unsigned long *flags)
 {
-	if (IS_ENABLED(CONFIG_RPS))
+	if (IS_ENABLED(CONFIG_RPS) || IS_ENABLED(CONFIG_PREEMPT_RT))
 		spin_unlock_irqrestore(&sd->input_pkt_queue.lock, *flags);
-	else if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+	else
 		local_irq_restore(*flags);
 }
 
 static inline void rps_unlock_irq_enable(struct softnet_data *sd)
 {
-	if (IS_ENABLED(CONFIG_RPS))
+	if (IS_ENABLED(CONFIG_RPS) || IS_ENABLED(CONFIG_PREEMPT_RT))
 		spin_unlock_irq(&sd->input_pkt_queue.lock);
-	else if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+	else
 		local_irq_enable();
 }