Introduce cpuset_cpus_allowed_fallback() helper to fix the cpuset problems
with select_fallback_rq(). It can be called from any context and can't use
any cpuset locks including task_lock(). It is called when the task doesn't
have online cpus in ->cpus_allowed but ttwu/etc must be able to find a
suitable cpu.
I am not proud of this patch. Everything which needs such a fact comment
can't be good even if correct. But I'd prefer to not change the locking
rules in the code I hardly understand, and in any case I believe this
simple change make the code much more correct compared to deadlocks we
currently have.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
include/linux/cpuset.h | 7 +++++++
kernel/sched.c | 4 +---
kernel/cpuset.c | 42 ++++++++++++++++++++++++++++++++++++++++++
3 files changed, 50 insertions(+), 3 deletions(-)
--- 34-rc1/include/linux/cpuset.h~6_FALLBACK_CPUSETS 2010-03-15 09:40:16.000000000 +0100
+++ 34-rc1/include/linux/cpuset.h 2010-03-15 09:42:08.000000000 +0100
@@ -21,6 +21,7 @@ extern int number_of_cpusets; /* How man
extern int cpuset_init(void);
extern void cpuset_init_smp(void);
extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
+extern int cpuset_cpus_allowed_fallback(struct task_struct *p);
extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
#define cpuset_current_mems_allowed (current->mems_allowed)
void cpuset_init_current_mems_allowed(void);
@@ -101,6 +102,12 @@ static inline void cpuset_cpus_allowed(s
cpumask_copy(mask, cpu_possible_mask);
}
+static inline int cpuset_cpus_allowed_fallback(struct task_struct *p)
+{
+ cpumask_copy(&p->cpus_allowed, cpu_possible_mask);
+ return cpumask_any(cpu_active_mask);
+}
+
static inline nodemask_t cpuset_mems_allowed(struct task_struct *p)
{
return node_possible_map;
--- 34-rc1/kernel/sched.c~6_FALLBACK_CPUSETS 2010-03-15 09:41:51.000000000 +0100
+++ 34-rc1/kernel/sched.c 2010-03-15 09:42:08.000000000 +0100
@@ -2292,9 ...
