On 8/6/19 4:15 PM, Jason Gunthorpe wrote:
From: Jason Gunthorpe <j...@mellanox.com>

A prior commit e0f3c3f78da2 ("mm/mmu_notifier: init notifier if necessary")
made an attempt at doing this, but had to be reverted as calling
the GFP_KERNEL allocator under the i_mmap_mutex causes deadlock, see
commit 35cfa2b0b491 ("mm/mmu_notifier: allocate mmu_notifier in advance").

However, we can avoid that problem by doing the allocation only under
the mmap_sem, which is already happening.

Since all writers to mm->mmu_notifier_mm hold the write side of the
mmap_sem reading it under that sem is deterministic and we can use that to
decide if the allocation path is required, without speculation.

The actual update to mmu_notifier_mm must still be done under the
mm_take_all_locks() to ensure read-side coherency.

Signed-off-by: Jason Gunthorpe <j...@mellanox.com>

Looks good to me.
Reviewed-by: Ralph Campbell <rcampb...@nvidia.com>
dri-devel mailing list

Reply via email to