On Tue, Nov 27, 2018 at 5:50 PM Chris Wilson chris@chris-wilson.co.uk wrote:
Quoting Daniel Vetter (2018-11-27 07:49:18)
On Thu, Nov 22, 2018 at 05:51:06PM +0100, Daniel Vetter wrote:
This is a similar idea to the fs_reclaim fake lockdep lock. It's fairly easy to provoke a specific notifier to be run on a specific range: Just prep it, and then munmap() it.
A bit harder, but still doable, is to provoke the mmu notifiers for all the various callchains that might lead to them. But both at the same time is really hard to reliable hit, especially when you want to exercise paths like direct reclaim or compaction, where it's not easy to control what exactly will be unmapped.
By introducing a lockdep map to tie them all together we allow lockdep to see a lot more dependencies, without having to actually hit them in a single challchain while testing.
Aside: Since I typed this to test i915 mmu notifiers I've only rolled this out for the invaliate_range_start callback. If there's interest, we should probably roll this out to all of them. But my undestanding of core mm is seriously lacking, and I'm not clear on whether we need a lockdep map for each callback, or whether some can be shared.
Cc: Andrew Morton akpm@linux-foundation.org Cc: David Rientjes rientjes@google.com Cc: "Jérôme Glisse" jglisse@redhat.com Cc: Michal Hocko mhocko@suse.com Cc: "Christian König" christian.koenig@amd.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: Mike Rapoport rppt@linux.vnet.ibm.com Cc: linux-mm@kvack.org Signed-off-by: Daniel Vetter daniel.vetter@intel.com
Any comments on this one here? This is really the main ingredient for catching deadlocks in mmu notifier callbacks. The other two patches are more the icing on the cake.
Thanks, Daniel
include/linux/mmu_notifier.h | 7 +++++++ mm/mmu_notifier.c | 7 +++++++ 2 files changed, 14 insertions(+)
diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h index 9893a6432adf..a39ba218dbbe 100644 --- a/include/linux/mmu_notifier.h +++ b/include/linux/mmu_notifier.h @@ -12,6 +12,10 @@ struct mmu_notifier_ops;
#ifdef CONFIG_MMU_NOTIFIER
+#ifdef CONFIG_LOCKDEP +extern struct lockdep_map __mmu_notifier_invalidate_range_start_map; +#endif
/*
- The mmu notifier_mm structure is allocated and installed in
- mm->mmu_notifier_mm inside the mm_take_all_locks() protected
@@ -267,8 +271,11 @@ static inline void mmu_notifier_change_pte(struct mm_struct *mm, static inline void mmu_notifier_invalidate_range_start(struct mm_struct *mm, unsigned long start, unsigned long end) {
mutex_acquire(&__mmu_notifier_invalidate_range_start_map, 0, 0,_RET_IP_);Would not lock_acquire_shared() be more appropriate, i.e. treat this as a rwsem_acquire_read()?
read lock critical sections can't create any dependencies against any other read lock critical section of the same lock. Switching this to a read lock would just render the annotation pointless (if you don't include at least some write lock critical section somewhere, but I have no idea where you'd do that). A read lock that you only ever take for reading essentially doesn't do anything at all.
So not clear on why you're suggesting this?
It's the exact same idea like fs_reclaim of intserting a fake lock to tie all possible callchains to a given functions together with all possible callchains from that function. Of course this is only valid if all NxM combinations could happen in theory. For fs_reclaim that's true because direct reclaim can pick anything it wants to shrink/evict. For mmu notifier that's true as long as we assume any mmu notifier can be in use by any process, which only depends upon sufficiently contrived/evil userspace.
I guess I could use lock_map_acquire/release() wrappers for this like fs_reclaim, would be a bit more clear. -Daniel