On Fri, 2019-10-04 at 15:38 +0200, Michal Hocko wrote: > On Fri 04-10-19 09:30:39, Qian Cai wrote: > > On Fri, 2019-10-04 at 15:07 +0200, Michal Hocko wrote: > > > On Fri 04-10-19 08:56:16, Qian Cai wrote: > > > [...] > > > > It might be a good time to rethink if it is really a good idea to dump_page() > > > > at all inside has_unmovable_pages(). As it is right now, it is a a potential > > > > deadlock between console vs memory offline. More details are in this thread, > > > > > > > > https://lore.kernel.org/lkml/1568817579.5576.172.camel@xxxxxx/ > > > > > > Huh. That would imply we cannot do any printk from that path, no? > > > > Yes, or use something like printk_deferred() > > This is just insane. The hotplug code is in no way special wrt printk. > It is never called from the printk code AFAIK and thus there is no real > reason why this particular code should be any special. Not to mention > it calls printk indirectly from a code that is shared with other code > paths. Basically, printk() while holding the zone_lock will be problematic as console is doing the opposite as it always needs to allocate some memory. Then, it will always find some way to form this chain, console_lock -> * -> zone_lock. > > > or it needs to rework of the current console locking which I have no > > clue yet. > > Yes, if the lockdep is really referring to a real deadlock which I > haven't really explored. >
