Messages in this thread Patch in this message | | | Date | Wed, 09 Dec 2009 10:15:01 -0000 | From | Thomas Gleixner <> | Subject | [patch 2/4] sched: Use rcu in sched_get/set_affinity() |
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tasklist_lock is held read locked to protect the find_task_by_vpid() call and to prevent the task going away. sched_setaffinity acquires a task struct ref and drops tasklist lock right away. The access to the cpus_allowed mask is protected by rq->lock.
rcu_read_lock() provides the same protection here.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de> --- kernel/sched.c | 16 ++++++---------- 1 file changed, 6 insertions(+), 10 deletions(-)
Index: linux-2.6-tip/kernel/sched.c =================================================================== --- linux-2.6-tip.orig/kernel/sched.c +++ linux-2.6-tip/kernel/sched.c @@ -6535,22 +6535,18 @@ long sched_setaffinity(pid_t pid, const int retval; get_online_cpus(); - read_lock(&tasklist_lock); + rcu_read_lock(); p = find_process_by_pid(pid); if (!p) { - read_unlock(&tasklist_lock); + rcu_read_unlock(); put_online_cpus(); return -ESRCH; } - /* - * It is not safe to call set_cpus_allowed with the - * tasklist_lock held. We will bump the task_struct's - * usage count and then drop tasklist_lock. - */ + /* Prevent p going away */ get_task_struct(p); - read_unlock(&tasklist_lock); + rcu_read_unlock(); if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL)) { retval = -ENOMEM; @@ -6636,7 +6632,7 @@ long sched_getaffinity(pid_t pid, struct int retval; get_online_cpus(); - read_lock(&tasklist_lock); + rcu_read_lock(); retval = -ESRCH; p = find_process_by_pid(pid); @@ -6652,7 +6648,7 @@ long sched_getaffinity(pid_t pid, struct task_rq_unlock(rq, &flags); out_unlock: - read_unlock(&tasklist_lock); + rcu_read_unlock(); put_online_cpus(); return retval;
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