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diff --git a/sys/compat/linuxkpi/common/include/linux/rwsem.h b/sys/compat/linuxkpi/common/include/linux/rwsem.h
--- a/sys/compat/linuxkpi/common/include/linux/rwsem.h
+++ b/sys/compat/linuxkpi/common/include/linux/rwsem.h
@@ -37,19 +37,40 @@
struct rw_semaphore {
struct sx sx;
+
+ /*
+ * Implementations of `down_{read,write}()` attempts a "try lock"
+ * first, and if they fail, they bump `waiters_count` and acquire the
+ * lock using the blocking call.
+ *
+ * `rwsem_is_contended()` uses `waiters_count` to determine if other
+ * threads are waiting for this lock. It assumes that the caller also
+ * acquired the lock, though it does not enforce this.
+ *
+ * Linux uses a wait list (with the accompanying lock) instead of a
+ * counter because the list is used for other operations.
+ */
+ int waiters_count;
};
-#define down_write(_rw) sx_xlock(&(_rw)->sx)
-#define up_write(_rw) sx_xunlock(&(_rw)->sx)
-#define down_read(_rw) sx_slock(&(_rw)->sx)
-#define up_read(_rw) sx_sunlock(&(_rw)->sx)
+void linuxkpi_init_rwsem(struct rw_semaphore *rw, const char *name);
+void linuxkpi_down_write(struct rw_semaphore *rw);
+void linuxkpi_up_write(struct rw_semaphore *rw);
+void linuxkpi_down_read(struct rw_semaphore *rw);
+void linuxkpi_up_read(struct rw_semaphore *rw);
+
+#define init_rwsem(_rw) linuxkpi_init_rwsem(_rw, rwsem_name("lnxrwsem"))
+#define down_write(_rw) linuxkpi_down_write(_rw)
+#define up_write(_rw) linuxkpi_up_write(_rw)
+#define down_read(_rw) linuxkpi_down_read(_rw)
+#define up_read(_rw) linuxkpi_up_read(_rw)
+
#define down_read_trylock(_rw) !!sx_try_slock(&(_rw)->sx)
#define down_read_killable(_rw) linux_down_read_killable(_rw)
#define down_write_trylock(_rw) !!sx_try_xlock(&(_rw)->sx)
#define down_write_killable(_rw) linux_down_write_killable(_rw)
#define downgrade_write(_rw) sx_downgrade(&(_rw)->sx)
#define down_read_nested(_rw, _sc) down_read(_rw)
-#define init_rwsem(_rw) linux_init_rwsem(_rw, rwsem_name("lnxrwsem"))
#define down_write_nest_lock(sem, _rw) down_write(_rw)
#ifdef WITNESS_ALL
@@ -67,16 +88,14 @@
struct rw_semaphore name; \
static void name##_rwsem_init(void *arg) \
{ \
- linux_init_rwsem(&name, rwsem_name(#name)); \
+ linuxkpi_init_rwsem(&name, rwsem_name(#name)); \
} \
SYSINIT(name, SI_SUB_LOCK, SI_ORDER_SECOND, name##_rwsem_init, NULL)
-static inline void
-linux_init_rwsem(struct rw_semaphore *rw, const char *name)
+static inline int
+rwsem_is_contended(struct rw_semaphore *sem)
{
-
- memset(rw, 0, sizeof(*rw));
- sx_init_flags(&rw->sx, name, SX_NOWITNESS);
+ return (sem->waiters_count > 0);
}
extern int linux_down_read_killable(struct rw_semaphore *);
diff --git a/sys/compat/linuxkpi/common/src/linux_rwsem.c b/sys/compat/linuxkpi/common/src/linux_rwsem.c
new file mode 100644
--- /dev/null
+++ b/sys/compat/linuxkpi/common/src/linux_rwsem.c
@@ -0,0 +1,50 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2013-2017 Mellanox Technologies, Ltd.
+ * Copyright (c) 2026 The FreeBSD Foundation
+ */
+
+#include <linux/rwsem.h>
+
+void
+linuxkpi_init_rwsem(struct rw_semaphore *rw, const char *name)
+{
+ memset(rw, 0, sizeof(*rw));
+ sx_init_flags(&rw->sx, name, SX_NOWITNESS);
+ /* `rw->waiters_count` is already zero. */
+}
+
+void
+linuxkpi_down_write(struct rw_semaphore *rw)
+{
+ if (!sx_try_xlock(&rw->sx)) {
+ /* `rw->waiters_count` is used by `rwsem_is_contended()`. */
+ rw->waiters_count++;
+ sx_xlock(&rw->sx);
+ rw->waiters_count--;
+ }
+}
+
+void
+linuxkpi_up_write(struct rw_semaphore *rw)
+{
+ sx_xunlock(&rw->sx);
+}
+
+void
+linuxkpi_down_read(struct rw_semaphore *rw)
+{
+ if (!sx_try_slock(&rw->sx)) {
+ /* `rw->waiters_count` is used by `rwsem_is_contended()`. */
+ rw->waiters_count++;
+ sx_slock(&rw->sx);
+ rw->waiters_count--;
+ }
+}
+
+void
+linuxkpi_up_read(struct rw_semaphore *rw)
+{
+ sx_sunlock(&rw->sx);
+}
diff --git a/sys/conf/files b/sys/conf/files
--- a/sys/conf/files
+++ b/sys/conf/files
@@ -4706,6 +4706,8 @@
compile-with "${LINUXKPI_C}"
compat/linuxkpi/common/src/linux_pci.c optional compat_linuxkpi pci \
compile-with "${LINUXKPI_C}"
+compat/linuxkpi/common/src/linux_rwsem.c optional compat_linuxkpi \
+ compile-with "${LINUXKPI_C}"
compat/linuxkpi/common/src/linux_tasklet.c optional compat_linuxkpi \
compile-with "${LINUXKPI_C}"
compat/linuxkpi/common/src/linux_idr.c optional compat_linuxkpi \
diff --git a/sys/modules/linuxkpi/Makefile b/sys/modules/linuxkpi/Makefile
--- a/sys/modules/linuxkpi/Makefile
+++ b/sys/modules/linuxkpi/Makefile
@@ -24,6 +24,7 @@
linux_pci.c \
linux_radix.c \
linux_rcu.c \
+ linux_rwsem.c \
linux_schedule.c \
linux_seq_buf.c \
linux_seq_file.c \

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