I hope Rafael will correct me if I am wrong, On 05/12, Oleg Nesterov wrote: > > On 05/11, Linus Torvalds wrote: > > > > On Sat, 12 May 2007, Oleg Nesterov wrote: > > > > > > without task_lock() we can see "p->mm != NULL" but not PF_BORROWED_MM. > > > > Let me explain it one more time: > > - shouldn't the *caller* protect this? > > > > Afaik, there's two situations: > > - either things don't change (in which case you don't need locking at > > all, since things are statically one way or the other) > > - or things change (in which case the caller can't rely on the return > > value anyway, since they might change *after* you release the lock) > > things change, ->mm is not stable if the kernel thread does use_mm/unuse_mm. > > However, the return value == 0 does not change in that particular case, > exactly because is_user_space() takes task_lock().
Probably there is some misunderstanding. This patch doesn't claim it solves all problems. Before this patch we have static inline int is_user_space(struct task_struct *p) { return p->mm && !(p->flags & PF_BORROWED_MM); } and this is clearly racy wrt to use_mm() which sets this PF_BORROWED_MM bit. So this is just a little improvement, nothing more. Oleg. - 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/