On Fri 16-08-19 09:19:06, Jason Gunthorpe wrote: > On Fri, Aug 16, 2019 at 10:10:29AM +0200, Michal Hocko wrote: > > On Thu 15-08-19 17:13:23, Jason Gunthorpe wrote: > > > On Thu, Aug 15, 2019 at 09:35:26PM +0200, Michal Hocko wrote: > > > > > > > > The last detail is I'm still unclear what a GFP flags a blockable > > > > > invalidate_range_start() should use. Is GFP_KERNEL OK? > > > > > > > > I hope I will not make this muddy again ;) > > > > invalidate_range_start in the blockable mode can use/depend on any sleepable > > > > allocation allowed in the context it is called from. > > > > > > 'in the context is is called from' is the magic phrase, as > > > invalidate_range_start is called while holding several different mm > > > related locks. I know at least write mmap_sem and i_mmap_rwsem > > > (write?) > > > > > > Can GFP_KERNEL be called while holding those locks? > > > > i_mmap_rwsem would be problematic because it is taken during the > > reclaim. > > Okay.. So the fs_reclaim debugging does catch errors. I do not think fs_reclaim is the udnerlying mechanism to catch this deadlock. It is a simple AA deadlock. You take i_mmap_rwsem and then go down the allocation path, direct reclaim and take the lock again. Nothing really surprising. fs_reclaim is really to catch GFP_NOFS context calling into a less restricted (e.g. GFP_KERNEL allocation context). > Do you have any > reference for what a false positive looks like? I believe I have given some examples when introducing __GFP_NOLOCKDEP. > I would like to inject it into the notifier path as this is very > difficult for driver authors to discover and know about, but I'm > worried about your false positive remark. > > I think I understand we can use only GFP_ATOMIC in the notifiers, but > we need a strategy to handle OOM to guarentee forward progress. Your example is from the notifier registration IIUC. Can you pre-allocate before taking locks? Could you point me to some examples when the allocation is necessary in the range notifier callback? -- Michal Hocko SUSE Labs _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
