5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
[ Upstream commit 3c118547f87e930d45a5787e386734015dd93b32 ]
On PREEMPT_RT the seqcount_t for synchronisation is required on 32bit
architectures even on UP because the softirq (and the threaded IRQ handler) can
be preempted.
With the seqcount_t for synchronisation, a reader with higher priority can
preempt the writer and then spin endlessly in read_seqcount_begin() while the
writer can't make progress.
To avoid such a lock up on PREEMPT_RT the writer must disable preemption during
the update. There is no need to disable interrupts because no writer is using
this API in hard-IRQ context on PREEMPT_RT.
Disable preemption on 32bit-RT within the u64_stats write section.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Stable-dep-of: 38a15d0a50e0 ("u64_stats: fix u64_stats_init() for lockdep when used repeatedly in one file")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
include/linux/u64_stats_sync.h | 42 ++++++++++++++++++++++------------
1 file changed, 28 insertions(+), 14 deletions(-)
diff --git a/include/linux/u64_stats_sync.h b/include/linux/u64_stats_sync.h
index e81856c0ba134..6a0f2097d3709 100644
--- a/include/linux/u64_stats_sync.h
+++ b/include/linux/u64_stats_sync.h
@@ -66,7 +66,7 @@
#include <linux/seqlock.h>
struct u64_stats_sync {
-#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
+#if BITS_PER_LONG == 32 && (defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT))
seqcount_t seq;
#endif
};
@@ -115,7 +115,7 @@ static inline void u64_stats_inc(u64_stats_t *p)
}
#endif
-#if BITS_PER_LONG == 32 && defined(CONFIG_SMP)
+#if BITS_PER_LONG == 32 && (defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT))
#define u64_stats_init(syncp) seqcount_init(&(syncp)->seq)
#else
static inline void u64_stats_init(struct u64_stats_sync *syncp)
@@ -125,15 +125,19 @@ static inline void u64_stats_init(struct u64_stats_sync *syncp)
static inline void u64_stats_update_begin(struct u64_stats_sync *syncp)
{
-#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
+#if BITS_PER_LONG == 32 && (defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT))
+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
+ preempt_disable();
write_seqcount_begin(&syncp->seq);
#endif
}
static inline void u64_stats_update_end(struct u64_stats_sync *syncp)
{
-#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
+#if BITS_PER_LONG == 32 && (defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT))
write_seqcount_end(&syncp->seq);
+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
+ preempt_enable();
#endif
}
@@ -142,8 +146,11 @@ u64_stats_update_begin_irqsave(struct u64_stats_sync *syncp)
{
unsigned long flags = 0;
-#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
- local_irq_save(flags);
+#if BITS_PER_LONG == 32 && (defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT))
+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
+ preempt_disable();
+ else
+ local_irq_save(flags);
write_seqcount_begin(&syncp->seq);
#endif
return flags;
@@ -153,15 +160,18 @@ static inline void
u64_stats_update_end_irqrestore(struct u64_stats_sync *syncp,
unsigned long flags)
{
-#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
+#if BITS_PER_LONG == 32 && (defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT))
write_seqcount_end(&syncp->seq);
- local_irq_restore(flags);
+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
+ preempt_enable();
+ else
+ local_irq_restore(flags);
#endif
}
static inline unsigned int __u64_stats_fetch_begin(const struct u64_stats_sync *syncp)
{
-#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
+#if BITS_PER_LONG == 32 && (defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT))
return read_seqcount_begin(&syncp->seq);
#else
return 0;
@@ -170,7 +180,7 @@ static inline unsigned int __u64_stats_fetch_begin(const struct u64_stats_sync *
static inline unsigned int u64_stats_fetch_begin(const struct u64_stats_sync *syncp)
{
-#if BITS_PER_LONG==32 && !defined(CONFIG_SMP)
+#if BITS_PER_LONG == 32 && (!defined(CONFIG_SMP) && !defined(CONFIG_PREEMPT_RT))
preempt_disable();
#endif
return __u64_stats_fetch_begin(syncp);
@@ -179,7 +189,7 @@ static inline unsigned int u64_stats_fetch_begin(const struct u64_stats_sync *sy
static inline bool __u64_stats_fetch_retry(const struct u64_stats_sync *syncp,
unsigned int start)
{
-#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
+#if BITS_PER_LONG == 32 && (defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT))
return read_seqcount_retry(&syncp->seq, start);
#else
return false;
@@ -189,7 +199,7 @@ static inline bool __u64_stats_fetch_retry(const struct u64_stats_sync *syncp,
static inline bool u64_stats_fetch_retry(const struct u64_stats_sync *syncp,
unsigned int start)
{
-#if BITS_PER_LONG==32 && !defined(CONFIG_SMP)
+#if BITS_PER_LONG == 32 && (!defined(CONFIG_SMP) && !defined(CONFIG_PREEMPT_RT))
preempt_enable();
#endif
return __u64_stats_fetch_retry(syncp, start);
@@ -203,7 +213,9 @@ static inline bool u64_stats_fetch_retry(const struct u64_stats_sync *syncp,
*/
static inline unsigned int u64_stats_fetch_begin_irq(const struct u64_stats_sync *syncp)
{
-#if BITS_PER_LONG==32 && !defined(CONFIG_SMP)
+#if BITS_PER_LONG == 32 && defined(CONFIG_PREEMPT_RT)
+ preempt_disable();
+#elif BITS_PER_LONG == 32 && !defined(CONFIG_SMP)
local_irq_disable();
#endif
return __u64_stats_fetch_begin(syncp);
@@ -212,7 +224,9 @@ static inline unsigned int u64_stats_fetch_begin_irq(const struct u64_stats_sync
static inline bool u64_stats_fetch_retry_irq(const struct u64_stats_sync *syncp,
unsigned int start)
{
-#if BITS_PER_LONG==32 && !defined(CONFIG_SMP)
+#if BITS_PER_LONG == 32 && defined(CONFIG_PREEMPT_RT)
+ preempt_enable();
+#elif BITS_PER_LONG == 32 && !defined(CONFIG_SMP)
local_irq_enable();
#endif
return __u64_stats_fetch_retry(syncp, start);
--
2.43.0
