On Tue, Jul 15, 2025 at 12:23:31PM +0200, Vlastimil Babka wrote: > On 7/15/25 11:52, David Hildenbrand wrote: > > On 15.07.25 11:40, Lorenzo Stoakes wrote: > >> On Tue, Jul 15, 2025 at 10:16:41AM +0200, Vlastimil Babka wrote: > >>>> Andrew, could you please remove this patchset from mm-unstable for now > >>>> until I fix the issue and re-post the new version? > >>> > >>> Andrew can you do that please? We keep getting new syzbot reports. > >> > >> I also pinged up top :P just to be extra specially clear... > >> > >>> > >>>> The error I got after these fixes is: > >>> > >>> I suspect the root cause is the ioctls are not serialized against each > >>> other > >>> (probably not even against read()) and yet we treat m->private as safe to > >>> work on. Now we have various fields that are dangerous to race on - for > >>> example locked_vma and iter races would explain a lot of this. > >>> > >>> I suspect as long as we used purely seq_file workflow, it did the right > >>> thing for us wrt serialization, but the ioctl addition violates that. We > >>> should rather recheck even the code before this series, if dangerous ioctl > >>> vs read() races are possible. And the ioctl implementation should be > >>> refactored to use an own per-ioctl-call private context, not the > >>> seq_file's > >>> per-file-open context. > >> > >> Entirely agree with this analysis. I had a look at most recent report, see: > >> > >> https://lore.kernel.org/linux-mm/f13cda37-06a0-4281-87d1-042678a38a6b@lucifer.local/ > >> > >> AFAICT we either have to lock around the ioctl or find a new way of storing > >> per-ioctl state. > >> > >> We'd probably need to separate out the procmap query stuff to do that > >> though. Probably. > > > > When I skimmed that series the first time, I was wondering "why are we > > even caring about PROCMAP_QUERY that in the context of this patch series". > > > > Maybe that helps :) > > Yeah seems like before patch 8/8 the ioctl handling, specifically > do_procmap_query() only looks at priv->mm and nothing else so it should be > safe as that's a stable value. > > So it should be also enough to drop the last patch from mm for now, not > whole series.
Yeah to save the mothership we can ditch the landing craft :P Maybe worth doing that, and figure out in a follow up how to fix this. Or we could just sling in a cheeky spinlock
