Gitweb:     http://git.kernel.org/linus/1445c08d06c5594895b4fae952ef8a457e89c390
Commit:     1445c08d06c5594895b4fae952ef8a457e89c390
Parent:     897f0b3c3ff40b443c84e271bef19bd6ae885195
Author:     Oleg Nesterov <oleg@redhat.com>
AuthorDate: Mon Mar 15 10:10:10 2010 +0100
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Fri Apr 2 20:12:01 2010 +0200

    sched: move_task_off_dead_cpu(): Take rq->lock around select_fallback_rq()
    
    move_task_off_dead_cpu()->select_fallback_rq() reads/updates ->cpus_allowed
    lockless. We can race with set_cpus_allowed() running in parallel.
    
    Change it to take rq->lock around select_fallback_rq(). Note that it is not
    trivial to move this spin_lock() into select_fallback_rq(), we must recheck
    the task was not migrated after we take the lock and other callers do not
    need this lock.
    
    To avoid the races with other callers of select_fallback_rq() which rely on
    TASK_WAKING, we also check p->state != TASK_WAKING and do nothing otherwise.
    The owner of TASK_WAKING must update ->cpus_allowed and choose the correct
    CPU anyway, and the subsequent __migrate_task() is just meaningless because
    p->se.on_rq must be false.
    
    Alternatively, we could change select_task_rq() to take rq->lock right
    after it calls sched_class->select_task_rq(), but this looks a bit ugly.
    
    Also, change it to not assume irqs are disabled and absorb __migrate_task_irq().
    
    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    LKML-Reference: <20100315091010.GA9131@redhat.com>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 kernel/sched.c |   30 +++++++++++++++---------------
 1 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index c0b3ebc..27774b5 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5448,29 +5448,29 @@ static int migration_thread(void *data)
 }
 
 #ifdef ...
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