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Subject[PATCH v2 1/2] cpu/hotplug: Add a cpus_read_trylock() function
Date
There are use cases where it can be useful to have a cpus_read_trylock()
function to work around circular lock dependency problem involving
the cpu_hotplug_lock.

Signed-off-by: Waiman Long <longman@redhat.com>
---
include/linux/cpu.h | 2 ++
kernel/cpu.c | 6 ++++++
2 files changed, 8 insertions(+)

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index a97a63e..e850bfe 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -103,6 +103,7 @@ static inline void cpu_maps_update_done(void)
extern void cpus_write_unlock(void);
extern void cpus_read_lock(void);
extern void cpus_read_unlock(void);
+extern int cpus_read_trylock(void);
extern void lockdep_assert_cpus_held(void);
extern void cpu_hotplug_disable(void);
extern void cpu_hotplug_enable(void);
@@ -115,6 +116,7 @@ static inline void cpus_write_lock(void) { }
static inline void cpus_write_unlock(void) { }
static inline void cpus_read_lock(void) { }
static inline void cpus_read_unlock(void) { }
+static inline int cpus_read_trylock(void) { return true; }
static inline void lockdep_assert_cpus_held(void) { }
static inline void cpu_hotplug_disable(void) { }
static inline void cpu_hotplug_enable(void) { }
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 0db8938..307486b 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -290,6 +290,12 @@ void cpus_read_lock(void)
}
EXPORT_SYMBOL_GPL(cpus_read_lock);

+int cpus_read_trylock(void)
+{
+ return percpu_down_read_trylock(&cpu_hotplug_lock);
+}
+EXPORT_SYMBOL_GPL(cpus_read_trylock);
+
void cpus_read_unlock(void)
{
percpu_up_read(&cpu_hotplug_lock);
--
1.8.3.1
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