Yang Shi wrote: > On 9/28/17 12:57 PM, Tetsuo Handa wrote: > > Yang Shi wrote: > >> On 9/27/17 9:36 PM, Tetsuo Handa wrote: > >>> On 2017/09/28 6:46, Yang Shi wrote: > >>>> Changelog v7 -> v8: > >>>> * Adopted Michal’s suggestion to dump unreclaim slab info when unreclaimable slabs amount > total user memory. Not only in oom panic path. > >>> > >>> Holding slab_mutex inside dump_unreclaimable_slab() was refrained since V2 > >>> because there are > >>> > >>> mutex_lock(&slab_mutex); > >>> kmalloc(GFP_KERNEL); > >>> mutex_unlock(&slab_mutex); > >>> > >>> users. If we call dump_unreclaimable_slab() for non OOM panic path, aren't we > >>> introducing a risk of crash (i.e. kernel panic) for regular OOM path? > >> > >> I don't see the difference between regular oom path and oom path other > >> than calling panic() at last. > >> > >> And, the slab dump may be called by panic path too, it is for both > >> regular and panic path. > > > > Calling a function that might cause kerneloops immediately before calling panic() > > would be tolerable, for the kernel will panic after all. But calling a function > > that might cause kerneloops when there is no plan to call panic() is a bug. > > I got your point. slab_mutex is used to protect the list of all the > slabs, since we are already in oom, there should be not kmem cache > destroy happen during the list traverse. And, list_for_each_entry() has > been replaced to list_for_each_entry_safe() to make the traverse more > robust. I consider that OOM event and kmem chache destroy event can run concurrently because slab_mutex is not held by OOM event (and unfortunately cannot be held due to possibility of deadlock) in order to protect the list of all the slabs. I don't think replacing list_for_each_entry() with list_for_each_entry_safe() makes the traverse more robust, for list_for_each_entry_safe() does not defer freeing of memory used by list element. Rather, replacing list_for_each_entry() with list_for_each_entry_rcu() (and making relevant changes such as rcu_read_lock()/rcu_read_unlock()/synchronize_rcu()) will make the traverse safe. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
