Commit b3426599 authored by Paul Jackson's avatar Paul Jackson Committed by Linus Torvalds
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[PATCH] cpuset semaphore depth check optimize

Optimize the deadlock avoidance check on the global cpuset
semaphore cpuset_sem.  Instead of adding a depth counter to the
task struct of each task, rather just two words are enough, one
to store the depth and the other the current cpuset_sem holder.

Thanks to Nikita Danilov for the idea.
Signed-off-by: default avatarPaul Jackson <>

[ We may want to change this further, but at least it's now
  a totally internal decision to the cpusets code ]
Signed-off-by: default avatarLinus Torvalds <>
parent f24ec7f6
......@@ -785,7 +785,6 @@ struct task_struct {
short il_next;
short cpuset_sem_nest_depth;
struct cpuset *cpuset;
nodemask_t mems_allowed;
int cpuset_mems_generation;
......@@ -180,6 +180,8 @@ static struct super_block *cpuset_sb = NULL;
static DECLARE_MUTEX(cpuset_sem);
static struct task_struct *cpuset_sem_owner;
static int cpuset_sem_depth;
* The global cpuset semaphore cpuset_sem can be needed by the
......@@ -200,16 +202,19 @@ static DECLARE_MUTEX(cpuset_sem);
static inline void cpuset_down(struct semaphore *psem)
if (current->cpuset_sem_nest_depth == 0)
if (cpuset_sem_owner != current) {
cpuset_sem_owner = current;
static inline void cpuset_up(struct semaphore *psem)
if (current->cpuset_sem_nest_depth == 0)
if (--cpuset_sem_depth == 0) {
cpuset_sem_owner = NULL;
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