On Fri 04-10-19 09:56:00, Qian Cai wrote: > 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. So this is not as much a hotplug specific problem but zone->lock -> printk -> alloc chain that is a problem, right? Who is doing an allocation from this atomic context? I do not see any atomic allocation in kernel/printk/printk.c. -- Michal Hocko SUSE Labs
