On 23.03.2015 22:10, Oleg Nesterov wrote:
On 03/23, Davidlohr Bueso wrote:void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file) { struct file *old_exe_file = rcu_dereference_protected(mm->exe_file, - !atomic_read(&mm->mm_users) || current->in_execve || - lock_is_held(&mm->mmap_sem)); + !atomic_read(&mm->mm_users) || current->in_execve);Thanks, looks correct at first glance... But can't we remove the ->in_execve check above? and check atomic_read(&mm->mm_users) <= 1 instead. OK, this is subjective, I won't insist. Just current->in_execve looks a bit confusing, it means "I swear, the caller is flush_old_exec() and this mm is actualy bprm->mm". "atomic_read(&mm->mm_users) <= 1" looks a bit more "safe". But again, I won't insist.
Not so safe: this will race with get_task_mm(). A lot of proc files grab temporary reference to task mm. But this just a debug -- we can place here "true".
Oleg.
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