oom_kill_process() does atomic_inc(&mm->mm_users) to ensure that this ->mm can't go away and this is wrong, change it to rely on ->mm_count and mmdrop().
Firstly, we do not want to delay exit_mmap/etc if the victim exits before we do mmput(), but this is minor. More importantly, we simply can not do mmput() in oom_kill_process(), this can deadlock. For example, suppose that access_process_vm(tsk) triggers OOM and oom-killer decides to kill this "tsk". If it exits and does mmput() before us, ksm_exit() called by us may want to want to take the same mmap_sem for writing. Signed-off-by: Oleg Nesterov <[email protected]> --- mm/oom_kill.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 034d219..52abb78 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -571,7 +571,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p, /* Get a reference to safely compare mm after task_unlock(victim) */ mm = victim->mm; - atomic_inc(&mm->mm_users); + atomic_inc(&mm->mm_count); /* * We should send SIGKILL before setting TIF_MEMDIE in order to prevent * the OOM victim from depleting the memory reserves from the user @@ -609,7 +609,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p, } rcu_read_unlock(); - mmput(mm); + mmdrop(mm); put_task_struct(victim); } #undef K -- 2.4.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
